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- Source title: A hierarchical Bayesian model for dynamic phenotypes in multi-environment trials with genotype by environment interaction
- Author(s): Shota Gugushvili, George A. K. van Voorn, Martin P. Boer, Daniela Bustos-Korts, Sandra Huynh Truong, Nicholas A. Friedenberg, Ryan McCormick, Scott Chapman, Carlos D. Messina, Fred A. van Eeuwijk
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# 1 A hierarchical Bayesian model for dynamic phenotypes in 2 multi-environment trials with genotype by environment interaction


3 Shota Gugushvili &#91;1,*&#93;, George A. K. van Voorn &#91;1&#93;, Martin P. Boer &#91;1&#93;, Daniela Bustos-Korts &#91;1,2&#93;,
4 Sandra Huynh Truong &#91;3&#93;, Nicholas A. Friedenberg &#91;3&#93;, Ryan McCormick &#91;3&#93;, Scott Chapman &#91;4&#93;,
5 Carlos D. Messina &#91;3,5&#93;, and Fred A. van Eeuwijk &#91;1,*&#93;


6 1 Mathematical and Statistical Methods group – Biometris, Wageningen University and Research, Wageningen,
7 The Netherlands
8 2 Institute of Plant Production and Protection, Faculty of Agricultural Sciences, Universidad Austral de Chile,
9 Valdivia, Chile
3
10 Research &amp; Development, Corteva Agriscience, Johnston, IA, United States
4
11 School of Agriculture and Food Sustainability, Faculty of Science, The University of Queensland, Gatton, QLD,
12 Australia
13 5 Department of Horticultural Sciences, University of Florida, Gainesville, FL, United States
             14 Corresponding authors: &#91;shota.gugushvili@wur.nl,&#93;(mailto:shota.gugushvili@wur.nl) &#91;fred.vaneeuwijk@wur.nl&#93;(mailto:fred.vaneeuwijk@wur.nl)


15 **Abstract**


16 New phenotyping tools produce longitudinal phenotypes that describe plant growth and devel17 opment. Estimates for the parameters that describe the dynamics of such longitudinal phenotypes
18 can be incorporated as predictors in models for static target traits like yield and biomass. Within a
19 hierarchical Bayesian context, we present a differential equation (DE) model for log-logistic growth in
20 longitudinal traits for sets of genotypes across multiple environments. The DE parameters coincide
21 with a midpoint, a slope, and an asymptote at the end of growth and development, i.e., final biomass.
22 Each DE parameter in our hierarchical model results from contributions of genotype, environment,
23 and _G × E_ . This formulation allows one to assess and quantify the genotype-specificity of the DE
24 parameters. When none of the DE parameters in our model requires a _G × E_ term, the dynamic
25 parameters characterizing the particular trait will be useful features for inclusion in prediction models
26 for yield or biomass. We fitted a DE model to APSIM-simulated longitudinal wheat biomass data
27 and quantified the contribution of genotype, environment and _G × E_ to the phenotypic variation in
28 the DE parameters. Only the upper asymptote showed clear _G × E_ . Estimates for genotypic and
29 _G × E_ parameters within the DE parameters were used to characterize genotypes. Estimates for
30 environmental and _G × E_ effects formed inputs for environmental characterization.


31 **Keywords:** crop growth model, genotype by environment interaction, phenomics, phenotyping,
32 process-based model, yield prediction


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## 33 1 Introduction


34 New phenotyping devices produce longitudinal data on many aspects of plant growth and development for
35 large collections of genotypes (Gu´edon et al., 2022). Depending on the device, these data have moderate to
36 high time resolution (Araus et al., 2018, 2022; Tardieu et al., 2017). The study of longitudinal phenotypic
37 traits is of interest in itself when these traits can be considered to represent yield components, i.e. they
38 bear a physiological relation to yield and reflect adaptation of the genotype to the environment. Knowledge
39 of the dynamics of yield components adds to biological insights in yield-producing processes and will
40 improve yield prediction models. Such improvements can cover both within-trial yield forecasts as well as
41 between-trial yield predictions where the longitudinal phenotyping information can be combined with
42 genomic information.
43 Beyond a small subset of longitudinal traits that can be considered to be directly or closely related to
44 yield, most longitudinal traits that are measured automatically or semi-automatically by proximate and
45 remote sensors initially lack a direct connection with plant physiological processes and structures. Such
46 traits are called secondary traits, and although they lack clear biological meaning, it can be worthwhile
47 to model their dynamics and estimate the corresponding parameters because aspects of their dynamical
48 behavior may improve prediction models for yield. When secondary traits or functions of secondary traits
49 contribute to the prediction of yield, then it is plausible that they represent proxies of physiologically
50 important traits, that is, yield components. Various articles offer guidelines on how to decompose yield
51 into components and which traits to phenotype as proxies to those components (Araus et al., 2018;
52 Tardieu et al., 2017; Bouidghaghen et al., 2023). These yield components characteristically reflect resource
53 capture and conversion into biomass and aspects of source-sink relations that lead to the prediction of the
54 fraction of biomass translated into yield (harvest index). A decomposition of yield into component traits
55 or processes immediately suggests yield prediction models that integrate information from multiple yield
56 components as measured by proxies. The yield components act as genotype-specific inputs. The prediction
57 model consists of a function that is able to convert the yield components together with some environmental
58 inputs into yield as output. Prediction models differ with respect to the yield components to be included
59 as static or dynamic quantities. The static yield components represent physiological constants that may be
60 observed in single well-conditioned experiments, while the dynamic yield components require longitudinal
61 observations. The environmental inputs are dynamical, but may differ at the aggregation level that is
62 incorporated. For example, temperatures may be chosen to be included as a daily or weekly mean.
63 Bouidghaghen et al. (2023) make a case for the breakdown of yield into a number of subprocesses and
64 structures, each of which can be measured by high-throughput robotized phenotyping devices at platforms.
65 They emphasize that before inserting traits measured on platforms into prediction models for yield in the
66 field, these traits require scaling, transformation, and conditioning on environmental variables such as, for
67 example, thermal time, soil water potential, and vapor pressure deficit. Although Bouidghaghen et al.
68 (2023) illustrate how to decompose yield and predict yield components from phenotyping and genomics,
69 they do not go all the way in formulating and comparing prediction models for yield from genotype-specific
70 and environmental inputs. The same approach to yield prediction via yield decomposition and component
71 approximation drives the work of other researchers that aims at the integration of longitudinal phenotyping
72 information and ultimately genomics into yield prediction models. Examples of this approach can be
73 found in Roth et al. (2021, 2022, 2023) and P´erez-Valencia et al. (2022, 2024). All of these papers focus
74 on one or a few longitudinal traits whose dynamics are modeled to extract summary statistics for eventual
75 prediction of yield in future environments. Again, this latter aspect is not explicitly elaborated.
76 The papers mentioned in the above paragraphs all depart from dynamical models for yield (or yield
77 components) that are based on physiological insights and help to define underlying yield components
78 that can either be measured by sensors in the field or on a platform or predicted from marker profiles
79 in an attempt to integrate phenotyping with genomics in the prediction of yield. The dynamical model
80 can be a fully developed ecophysiological model, such as in Technow et al. (2015) and Messina et al.
81 (2018), or more data driven as in the case of Roth et al. (2021, 2022) and P´erez-Valencia et al. (2022,
82 2024). In all cases, an important consideration in the use of longitudinal phenotypic information for
83 yield prediction is that the dynamics of the longitudinal trait itself, say the defining parameters, are not
84 subject to strong genotype by environment interaction, _G × E_, themselves (Poudel et al., 2023; Roth
85 et al., 2023). The idea here is that parameters describing longitudinal yield components will enter as
86 genotype-specific static inputs into yield generating functions together with dynamical environmental
87 inputs. When genotype-specific inputs do not show _G × E_, or when they show a simple type of _G × E_
88 that can be scaled, transformed, or conditioned on an environmental covariable (Bouidghaghen et al.,
89 2023), they can be measured or estimated in a single platform or field experiment. _G × E_ for yield then


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90 needs to emerge from the yield generating function.
91 The objective of this paper is to investigate a class of statistical models for analyzing longitudinal
92 trait data for a population of genotypes observed by one or more phenotyping devices in a series of
93 environments. The longitudinal traits may have been chosen after a prior yield decomposition and the
94 expectation is that the parameters describing the longitudinal behavior of the component trait will exhibit
95 relatively little _G × E_ and that they will ultimately contribute to a better yield prediction. For improved
96 yield prediction, we may later need to combine dynamic information on multiple yield components and
97 environmental inputs, but on the road to a robust predictive model, we first need to develop adequate
98 models for describing individual longitudinal traits. We aim for a modeling framework for our individual
99 longitudinal traits that is flexible in the kind of functions and parameterizations that can be chosen to
100 describe the dynamics of the trait. Simultaneously, across the entire set of genotypes and environments,
101 we would like to test and quantify the amount of _G × E_ in each of our dynamic parameters, using the
102 same inferential scheme that was used to estimate these parameters.
103 We will elaborate here the modeling concepts for plant growth that were introduced in Van Voorn et al.
104 (2023). In that paper, simple differential equation (DE) models with few state variables and parameters
105 were presented that were derived from first principles. Subsequently, these models were fitted per genotype
106 and per trial, that is, the estimation process was done separately for each combination of genotype and
107 environment without borrowing information between genotypes or environments, although it can be
108 assumed that a population of genotypes will show similar growth patterns over time just as environments
109 with comparable stress will do. Fitting dynamic models for single genotype by environment combinations
110 is feasible when the time resolution for observations is high, say, daily to a few times per week (Roth
111 et al., 2021, 2022; Shao et al., 2026). However, such a resolution is not realistic for most field situations.
112 Longitudinal trait data produced by drones in outside-field experiments typically consist of series of 10 to
113 15 time points in a growing season. For such medium-resolution temporal data, borrowing information
114 between genotypes in the fitting process will be beneficial, and very likely the same is true for borrowing
115 information between environments. With medium-resolution secondary phenotypes in mind, we present
116 here a hierarchical Bayesian framework for the simultaneous fitting of dynamic models on longitudinal
117 trait data for populations of genotypes across multiple environments. This framework allows borrowing
118 of information between genotypes and environments and has as further advantages the use of shrinkage
119 estimation of the dynamical parameters as well as appropriate propagation of uncertainty on parameter
120 estimates and phenotypic predicted values. As the most distinguishing feature, our framework expresses
121 dynamic parameters as functions of genotypic, environmental, and _G × E_ terms in a fashion reminiscent of
122 generalized linear mixed models (GLMMs). The decomposition of the phenotypic variation of the dynamic
123 parameters into components attributable to genotype, environment, and _G × E_ provides information on
124 the genotype specificity of these parameters and the genotypic and environmental drivers of dynamic
125 behavior. An example analysis on APSIM simulated wheat ( _Triticum_ _aestivum_ L.) biomass data, the
126 generation of which is described in Bustos-Korts et al. (2019a,b), illustrates the machinery of our Bayesian
127 hierarchical approach together with the interpretation of the estimates of the genotypic and environmental
128 contributions to the DE parameters.

## 129 2 Materials and methods


130 In this section, we present key aspects of our approach. We first give a rough and intuitive sketch of our
131 approach and philosophy. We then recall a phenomenological model from Van Voorn et al. (2023) and
132 show how a modification of it can be embedded within a statistical model. The resulting model will be
133 fitted via a Bayesian approach. An APSIM simulated wheat dataset is used to illustrate and investigate
134 the practical performance of our method.


135 **2.1** **A** **sketch** **of** **our** **hierarchical** **approach**


136 In a generic notation, we can write the signal part of the dynamics of the _s_ _&#91;th&#93;_ secondary trait for a genotype,
137 _i_, in an environment, _j_, as:


d _x_ _ij,s_ ( _t_ ) = _f_ ( _x_ _ij,s_ ( _t_ ) _, θ_ _ij_ _, z_ _j_ ( _t_ )) _._

d _t_


138 Here _x_ _ij,s_ ( _t_ ) represents, for genotype _i_ in environment _j_, an error free time-dynamic secondary trait, _s_,
139 such as biomass. The variable _z_ _j_ ( _t_ ) describes a vector of time-dynamical exogenous inputs, such as one or
140 more soil properties, minimum, mean and maximum temperatures, and precipitation. The DE or process


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Table 1: Explanations of the symbols and abbreviations used throughout this paper.


**Symbol** **Meaning**


CGM (abbr.) Crop Growth Model
DE (abbr.) Differential Equation
GLMM (abbr.) Generalized Linear Mixed Model
_G × E_ (abbr.) Genotype-by-Environment Interaction
WGP (abbr.) Whole Genome Prediction


_t_ Continuous time variable

_i_ Index for genotype
_j_ Index for trial (location _×_ year)
_k_ Index for time (discrete)
_p_ Superscript for DE parameter
_s_ Subscript to indicate secondary trait


_x_ _ij,s_ ( _t_ ) Secondary trait state variable
_y_ _ijk_ Observation at time _t_ _k_
_z_ _j_ ( _t_ ) Exogenous (environmental) input
_σ_ Standard deviation
_θ_ _ij_ Parameter (generic)
_µ_ Intercept for DE parameter
_α_ _i_ Genotypic effect on DE parameter
_β_ _j_ Trial effect on DE parameter
( _α · β_ ) _ij_ Interaction effect on DE parameter


_M_ ( _t_ ) Total biomass (time-dependent)
_r_ Crop growth rate
_M_ _&#91;max&#93;_ Maximum attainable biomass
_t_ _&#91;mid&#93;_ Midpoint


_∼_ Symbol for ‘distributed according to’
_N_ ( _µ, σ_ ) Normal distribution with mean _µ_ and standard deviation _σ_
Exponential( _λ_ ) Exponential distribution with rate parameter _λ_
HalfNormal( _µ, σ_ ) Half-Normal distribution with parameters _µ_ _σ_


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141 parameters are contained in the vector _θ_ _ij_ . From this ingredient we build a nonlinear mixed model, in
142 which each DE parameter is related to a linear mixed predictor through a log link, in the spirit of a
143 GLMM. In particular, the hierarchical system we propose can be thought of as containing an extra level
144 of modeling in defining GLMMs for each of the DE parameters: _g_ ( _θ_ _ij_ ) = _Xγ_, where the link function
145 _g_ ( _·_ ) works on the expectation of _θ_ _ij_ and is linear in the regression parameters _γ_, with design matrix _X_ .
146 The GLMMs for the DE parameters will include a general intercept, a genotypic main effect term, an
147 environmental main effect term, and a _G × E_ term. This formulation allows testing explicitly for the
148 inclusion of _G × E_ terms in the GLMMs for the individual DE parameters. Subsets of genotypes and
149 environments for whose dynamics no _G_ _×_ _E_ terms are needed act in what we can call a genetically additive
150 way, i.e., it suffices to estimate the differences between genotypes in a single environment because the same
151 genotypic differences will occur in any environment in which the genotypes will be grown, i.e. predictions
152 are valid for any environment. To obtain a genomic prediction model, the genotypic main effects can
153 be replaced or approximated by penalized regressions on marker profiles. It is important to note that
154 additivity of genotype and environment for the DE parameters does not exclude _G × E_ at the level of the
155 dynamic trait itself because the non-linearity of the DE system can still create _G × E_ as an emerging
156 property on top of DE parameters that behave additively with respect to genotype and environment.


157 **2.2** **Phenomenological** **model**


158 Van Voorn et al. (2023) discuss four models that reflect some essential characteristics of crop growth.
159 These models are of low complexity, while being time-dynamical, as well as phenomenological in nature,
160 and offer a biological interpretation of their parameters. According to Van Voorn et al. (2023), genotypic
161 variation can be conceptualized as genotype-related differences in parameter values, while dependence
162 on environmental or management inputs can be explicitly introduced by making the model parameters
163 functions of such inputs.
164 In this paper, we focus on a logistic model for biomass in wheat. This is the most basic model in
165 Van Voorn et al. (2023), which we will combine with a hierarchical Bayesian modeling approach. The
166 resulting statistical model is flexible enough to reach non-trivial inferential conclusions. In addition,
167 the logistic model serves as a useful baseline against which other approaches can be benchmarked and
168 compared. Furthermore, there is room to explore common numerical challenges in nonlinear regression
169 and fitting of ordinary differential equation (ODE) models (Seber and Wild, 1989; Ramsay and Hooker,
170 2017), as well as to examine the scalability of the method to large data.


171 **2.2.1** **Logistic** **model**


172 In the notation of Van Voorn et al. (2023), the logistic model is given by the ODE



1 _−_ _&#91;M&#93;_ &#91;(&#93; _&#91;t&#93;_ &#91;)&#93;
_M_ _&#91;max&#93;_ )︃



d _M_ ( _t_ ) = _rM_ ( _t_ )

d _t_



(︃



173 with an explicit solution



_M_ _&#91;max&#93;_
_M_ ( _t_ ) =



1 +
(



_,_ _M_ (0) = _M_ 0 _,_ (1)


_._ (2)

exp( _−rt_ )



_M_ _&#91;max&#93;_



)



_−_ 1
_M_ 0



174 Here _M_ ( _t_ ) is the total biomass at time _t_, the positive parameter _r_ is an intrinsic growth rate, while the
175 positive parameter _M_ _&#91;max&#93;_ is an intrinsic growth limitation or asymptote. Depending on the context, the
176 initial condition _M_ 0 can be interpreted either as the seed weight, or as the biomass at the starting day of

177 measurement.
178 In the literature there exist several alternative parameterizations of the logistic model (1) – (2), see, e.g.,
179 Seber and Wild (1989) and Pinheiro and Bates (2000). In one parameterization, the three parameters of
180 the model are the intrinsic growth rate _r_, the intrinsic growth limitation or asymptote _M_ _&#91;max&#93;_, and the
181 midpoint.



_−_ 1

)︃



_t_ _&#91;mid&#93;_ = &#91;1&#93; _r_ &#91;log&#93;



_M_ _max_
(︃ _M_ 0



_,_



182 where the biomass _M_ ( _t_ _&#91;mid&#93;_ ) = _M_ _&#91;max&#93;_ _/_ 2 _._ Here we implicitly assume that _M_ 0 _&lt; M_ _&#91;max&#93;_ . The function itself
183 is then given by

_M_ _&#91;max&#93;_
_M_ ( _t_ ) = 1 + exp( _−r_ ( _t −_ _t_ _&#91;mid&#93;_ )) _&#91;.&#93;_ (3)


184 This parameterization will be the basis for our subsequent arguments.


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185 **2.2.2** **Log-logistic** **model**


186 Successful fitting of nonlinear regression models to the data is strongly dependent on the chosen parameter187 ization of the function to be fitted (Seber and Wild, 1989, pp. 673–674). For example, a reparameterization
188 of a nonlinear model could remedy parameter identifiability (Seber and Wild, 1989, p. 103). A suitable
189 reparameterization of a model could likewise improve the convergence of an iterative non-linear optimiza190 tion algorithm (Seber and Wild, 1989, pp. 95–97), or, in the context of the present paper, convergence of
191 an MCMC sampler. Ross (1990) contains further discussion on these topics.
192 A modified version of the logistic model (1) – (2), termed the log-logistic model, turned out to be
193 numerically easier and faster to fit in the hierarchical modeling context than the basic logistic model. This
194 appears to be caused by algorithmic peculiarities of our MCMC sampler. In general, both the logistic and
195 log-logistic curves can be expected to give visually quite similar fits.
196 The log-logistic growth function closely resembles the logistic model (3) and is given by


︁



_M_ _&#91;max&#93;_
_M_ ( _t_ ) =

︁



)︁ _−r_ _&#91;.&#93;_ (4)



1 + ( _t_ _&#91;mid&#93;_ _t_ ︁



︁


197 The three parameters of the log-logistic model have an intuitive interpretation similar to the parameters of
198 the logistic model: _M_ _&#91;max&#93;_ is the intrinsic growth limitation. Next, _t_ _&#91;mid&#93;_ is the time point where response
199 _M_ ( _t_ _&#91;mid&#93;_ ) = _M_ _&#91;max&#93;_ _/_ 2. Finally, the parameter _r_ is the scaled slope at the midpoint. See Ritz et al. (2020)
200 for additional details.
201 The log-logistic model is by far the most common dose response model (Ritz et al., 2020, p. 178).
202 Its name reflects the fact that the function is obtained by rescaling the log-logistic distribution, which
203 in economics is known as the Fisk distribution. The log-logistic distribution also arises in the survival
204 analysis context (Bennett, 1983). Its mathematical properties make it suitable for crop growth modeling
205 as well, and in fact the model has been used in the agricultural setting: some references are listed in Focke
206 et al. (2017).
207 The differential equation for the log-logistic growth model away from the time origin _t_ = 0 can be
208 shown to be
d _M_ ( _t_ )

_&#91;r&#93;_ _&#91;M&#93;_ &#91;(&#93; _&#91;t&#93;_ &#91;)&#93;



︁


)︃



︁


= _&#91;r&#93;_
d _t_ _t_



︁


_t_ _&#91;M&#93;_ &#91;(&#93; _&#91;t&#93;_ &#91;)&#93;



︁


(︃



︁


1 _−_ _&#91;M&#93;_ &#91;(&#93; _&#91;t&#93;_ &#91;)&#93;
_M_ _&#91;max&#93;_



︁


_._ (5)



︁


209 The initial condition is _M_ ( _t_ _&#91;mid&#93;_ ) = _M_ _&#91;max&#93;_ _/_ 2 _,_ and the equation is thus understood to operate forward and
210 backward in time. When fitting the log-logistic model to data, we will rely on the explicit form (4) rather
211 than the differential equation formulation (5). See Section 2.5 ahead.


212 **2.3** **Data** **description**


213 To illustrate our method, we chose the same simulated longitudinal wheat data as in Van Voorn et al. (2023).
214 The crop growth simulation platform was APSIM-Wheat (Keating et al., 2003; Holzworth et al., 2018).The
215 data consist of biweekly (i.e. successive measurements spaced two weeks apart) biomass observations over
216 the growing season for an Australian diversity panel with originally 199 wheat genotypes (Zheng et al.,
217 2013) observed at four locations over 31 growing seasons (years); see Bustos-Korts et al. (2019a) and
218 Bustos-Korts et al. (2019b). The biweekly observations were chosen to reflect typical medium-resolution
219 temporal data that are similar to drone imagery observations for biomass. The complete data set is
220 available online (Bustos-Korts, 2023). For computational convenience, we drew a genetically representative
221 subset of 48 genotypes from the entire set of 199 genotypes (see the code referred to in the Software
222 section). This subsetting of genotypes allowed us to do all calculations described in this paper on a laptop
223 (MacBook Air, 2020, with Apple M1 chip with 8 cores, 4 for performance and 4 for efficiency, and 8 GB
224 RAM). The four locations chosen (Emerald, Narrabri, Yanco, Merredin) corresponded to environmentally
225 contrasting wheat growing areas in the Australian wheat belt. The environments in this paper are a
226 subset of the environments described in Casadebaig et al. (2016) and Chenu et al. (2013).
227 The first 14 days of biomass data after sowing were discarded, as these biomasses were (near) zero,
228 which presented numerical problems for fitting. The biomass given in kg ha _&#91;−&#93;_ &#91;1&#93; was converted into tons
229 ha _&#91;−&#93;_ &#91;1&#93;, and the time in days was re-scaled by a factor of 10, so that a new time unit corresponded to 10
230 days. These transformations bring both variables to the same scale and can be expected to help with
231 non-linear fitting, for instance because the population level parameters are then of the same order of
232 magnitude (Seber and Wild, 1989, p. 674).
233 At this stage of research, we preferred simulated data over field trial data. This choice allows for an
234 objective assessment of our approach against the ground truth. On the environmental side, the data were


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235 qualitatively characterized by the type of limitation (e.g. temperature or water) and quantitatively by
236 the level of environmental stress. On the genetic side, the data showed qualitative differences induced by
237 genotypes. Bustos-Korts et al. (2019a) and Bustos-Korts et al. (2019b) chose genotypic specifications of
238 crop growth parameters that mimic realistic genetic variation for Australian environmental conditions.


239 **2.4** **Bayesian** **approach**


240 Hierarchical models, of which our statistical model is a representative, lend themselves naturally to a
241 Bayesian approach. Moreover, in our experience with hierarchical models, modern Bayesian software such
242 as **Stan** is less prone to numerical failure than the off-the-shelf nonlinear least squares methods in **R** that
243 were used by Van Voorn et al. (2023). See Comets et al. (2017), Driver and Voelkle (2018) and Plan et al.
244 (2012) for a detailed discussion on algorithmic convergence issues in this context.
245 A data generating mechanism in a Bayesian model is described through the likelihood function. In
246 line with typical assumptions of additive and normally distributed measurement errors, we assumed that
247 the likelihood function was Gaussian and centered on values _M_ ( _t_ _k_ ) at observation points _t_ _k_, and had a
248 constant standard deviation _σ._

249 Another mandatory ingredient of Bayesian approach is a prior distribution on the model parameters.
250 This is a probability distribution that reflects one’s prior knowledge on model parameters. It can also be
251 viewed as a penalty or regularization term in the estimation procedure. Transtrum et al. (2011) explain
252 the usefulness of priors as penalty terms in the context of non-linear least squares estimation. Our exact
253 prior specifications will be given later on.
254 Except for simple statistical models, the posterior distribution is rarely available in analytic form.
255 To address this issue, over the years powerful Markov Chain Monte Carlo (MCMC) methods have been
256 developed to approximate posterior distribution through random sampling; see Brooks et al. (2011) for
257 an overview. In general, MCMC methods are regarded as the gold standard for approximate posterior
258 inference in that, in a long run, they provide asymptotically exact posterior samples. Their accuracy is
259 offset by constraints of scalability and computational feasibility. Other options to approximate the posterior
260 include variational inference (Blei et al., 2017), sequential Monte Carlo (Chopin and Papaspiliopoulos,
261 2020), Approximate Bayesian Computation (ABC) (Sisson et al., 2019), and the integrated nested Laplace
262 approximation (INLA) (G´omez-Rubio, 2020).


263 **2.5** **Bayesian** **hierarchical** **model**



264 The log-logistic model (4) was used to develop a hierarchical Bayesian model (Gelman and Hill, 2006;
265 Gelman et al., 2014) for the APSIM wheat data from Section 2.3. The underlying idea of hierarchical
266 modeling is that even though genotypes differ from each other, they have common features, and one
267 can attempt to exploit this when fitting a model to the data. A similar idea applies to environmental
268 variations over multiple years. As a result, data are used more efficiently, which, in principle, should
269 lead to more accurate parameter estimates and a better quantification of the remaining uncertainty
270 in inferential conclusions. This becomes particularly important in the real data setting where biomass
271 measurements are obtained through relatively infrequent drone flights; see Chen et al. (2022), Smith et al.
272 (2021), Panday et al. (2020a), Panday et al. (2020b) for an overview of longitudinal drone imagery.
273 In a nutshell, we assume that dynamics of crop growth in each trial and for each genotype can be
274 described by a log-logistic function with an own set of parameters, whereas the remaining variation is
275 attributed to statistical noise. The three parameters of the log-logistic function are themselves driven
276 by genetic and environmental information. In the next step, we assume that parameters across trials
277 and genotypes are linked through an overarching distribution. Inference is to be conducted on this
278 latter distribution. The resulting statistical model is dynamic, but embedded within the mixed modeling
279 framework at the parameter level (Pinheiro and Bates, 2000; Lee, 2022).
280 For the model description below, we provide a Kruschke-style diagram, cf. Kruschke (2014), in Figure
281 1. We use the following notation throughout: _y_ _ijk_ is the biomass measurement at time _t_ _k_ for genotype _i_
282 and trial _j._ Next, _M_ _ijk_ = _M_ ( _t_ _k_ ; _θ_ _ij_ ) is the value of the log-logistic function at time _t_ _k_ for genotype _i_ and
283 trial _j._ The parameter _θ_ _ij_ is a three-dimensional vector, its coordinates being logarithms of the maximum

284 or right asymptotic biomass _M_ _ij_ _&#91;max&#93;_, midpoint time _t_ _&#91;mid&#93;_ _ij_ and growth rate _r_ _ij_, respectively (for economy of
285 notation, here we have redefined parameters _θ_ _ij_ from Section 2.1 to their logarithms). Finally, _σ_ is the
286 measurement noise level.

287 As the construction is the same for each of the parameters of the log-logistic function, we focus on the


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288 right asymptote _M_ _&#91;max&#93;_ in our presentation. Our key assumption is the decomposition



_ij_ _&#91;max&#93;_ = exp( _µ_ _&#91;M&#93;_ + _α_ _i_ _&#91;M&#93;_



_j_ _&#91;M&#93;_ + ( _α · β_ ) _&#91;M&#93;_ _ij_



_ij_ &#91;)&#93; _&#91;.&#93;_ (6)



_M_ _&#91;max&#93;_



_i_ _&#91;M&#93;_ + _β_ _&#91;M&#93;_



289 The exponentiation is to ensure positivity of the parameter, whereas working on the logarithmic scale
290 enables one to build into it a two-way analysis of variance or ANOVA model structure



_θ_ _&#91;M&#93;_



_ij_ _&#91;M&#93;_ &#91;=&#93; _&#91; µ&#93;_ _&#91;M&#93;_ &#91;+&#93; _&#91; α&#93;_ _i_ _&#91;M&#93;_



_i_ _&#91;M&#93;_ + _β_ _&#91;M&#93;_



_j_ _&#91;M&#93;_ + ( _α · β_ ) _&#91;M&#93;_ _ij_



_ij_



291 with, obviously, _θ_ _ij_ _&#91;M&#93;_ &#91;=&#93; &#91; log&#93; &#91;(&#93; _&#91;M&#93;_ _&#91; max&#93;_ _ij_ ). Next, _µ_ _&#91;M&#93;_ can be thought of as the intercept common to all genotypes

292 and trials. The term _α_ _i_ _&#91;M&#93;_ is contribution of the genotype _i_ (on the logarithmic scale) to the DE parameter

293 _M_ _ij_ _&#91;max&#93;_ . Similarly, _β_ _j_ _&#91;M&#93;_ models the effect of specific environmental and management conditions in the trial _j_

294 on the DE parameter _M_ _ij_ _&#91;max&#93;_ . Finally, ( _α · β_ ) _&#91;M&#93;_ _ij_ &#91;is&#93; &#91;the&#93; &#91;interaction&#93; &#91;term&#93; &#91;for&#93; &#91;genotype&#93; _&#91;i&#93;_ &#91;and&#93; &#91;trial&#93; _&#91;j.&#93;_ &#91;We&#93; &#91;treat&#93;

295 _α_ _i_ _&#91;M&#93;_ &#91;’&#93; &#91;s,&#93; _&#91;β&#93;_ _j_ _&#91;M&#93;_ &#91;’&#93; &#91;s&#93; &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;M&#93;_ _ij_ &#91;’&#93; &#91;s&#93; &#91;as&#93; &#91;random&#93; &#91;effects;&#93; &#91;see,&#93; &#91;for&#93; &#91;example,&#93; &#91;Pinheiro&#93; &#91;and&#93; &#91;Bates&#93; &#91;(&#93;&#91;2000&#93;&#91;).&#93; &#91;The&#93; &#91;linear&#93;

296 model formulation for the logarithm of _M_ _ij_ _&#91;max&#93;_ is an example of a GLMM (Searle et al., 2006; Faraway,
297 2016) for a DE parameter embedded in our hierarchical Bayesian framework for multi-genotype multi298 environment dynamic data. This GLMM-like embedding offers a very powerful and versatile modeling
299 framework with options for quantification of genotypic and environmental contributions to dynamic trait
300 behavior.

301 The interpretability of the parameters of the log-logistic function can be directly leveraged to set priors
302 in the Bayesian model. The intercept _µ_ _&#91;M&#93;_ is assigned the prior



with, obviously, _θ_ _&#91;M&#93;_



_ij_ _&#91;M&#93;_ &#91;=&#93; &#91; log&#93; &#91;(&#93; _&#91;M&#93;_ _&#91; max&#93;_ _ij_



_ij_ _&#91;max&#93;_ . Similarly, _β_ _j_ _&#91;M&#93;_



_ij_ _&#91;max&#93;_ . Finally, ( _α · β_ ) _&#91;M&#93;_ _ij_



_i_ _&#91;M&#93;_ &#91;’&#93; &#91;s,&#93; _&#91;β&#93;_ _&#91;M&#93;_



_j_ _&#91;M&#93;_ &#91;’&#93; &#91;s&#93; &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;M&#93;_ _ij_



_µ_ _&#91;M&#93;_ _∼_ _N_ (2 _,_ 2) _._


303 This prior is weakly informative: the distribution covers a likely range of the logarithm of the biomass
304 measured at the end of the growing season for the APSIM data, while still allowing for a significant
305 variation.

306 The genotype random effects _α_ _i_ _&#91;M&#93;_ are assigned a prior through a hierarchical construction:



_i_ _&#91;M&#93;_ _∼_ _N_ (0 _, σ_ _α_ _&#91;M&#93;_



_α_ _&#91;M&#93;_



_α_ &#91;)&#93; _&#91;,&#93;_



_σ_ _α_ _&#91;M&#93;_ _&#91;∼&#93;_ &#91;Exponential(1)&#93; _&#91;.&#93;_



307 Similarly, for the trial random effects _β_ _j_ _&#91;M&#93;_ we assume



_j_ _&#91;M&#93;_ _∼_ _N_ (0 _, σ_ _β_ _&#91;M&#93;_



_β_ _&#91;M&#93;_



_β_ &#91;)&#93; _&#91;,&#93;_



_σ_ _β_ _&#91;M&#93;_ _&#91;∼&#93;_ &#91;Exponential(1)&#93; _&#91;.&#93;_



308 Also, these priors are weakly informative: the exponential distribution Exponential (1) has mean equal to

309 1. As a result, conditional on the values of _σ_ _α_ _&#91;M&#93;_ &#91;and&#93; _&#91;σ&#93;_ _β_ _&#91;M&#93;_ _&#91;,&#93;_ &#91;the&#93; &#91;parameters&#93; _&#91;α&#93;_ _i_ _&#91;M&#93;_ and _β_ _j_ _&#91;M&#93;_ are assigned a broad
310 prior, which nevertheless has a regularizing effect.
311 Finally, for the interaction random effect terms we assume



_β_ _&#91;M&#93;_ _&#91;,&#93;_ &#91;the&#93; &#91;parameters&#93; _&#91;α&#93;_ _i_ _&#91;M&#93;_



_i_ _&#91;M&#93;_ and _β_ _&#91;M&#93;_




_&#91;M&#93;_ _ij_ _&#91;∼&#93;_ _&#91;N&#93;_ &#91;(0&#93; _&#91;, σ&#93;_ ( _&#91;M&#93;_ _α_



( _α · β_ ) _&#91;M&#93;_



( _α·β_ ) &#91;)&#93; _&#91;,&#93;_



_σ_ ( _&#91;M&#93;_ _α·β_ ) _&#91;∼&#93;_ &#91;Exponential(1)&#93; _&#91;.&#93;_



Priors used for parameters _t_ _&#91;mid&#93;_



312 Priors used for parameters _t_ _ij_ and _r_ _ij_ can be found in the Supplementary Material accompanying

313 the article. Like for _M_ _&#91;max&#93;_ the is a ANOVA structure



313 the article. Like for _M_ _ij_ _&#91;max&#93;_, the key assumption is a two-way ANOVA structure



_r_ _ij_ = exp( _θ_ _ij_ _&#91;r&#93;_



_ij_ _&#91;r&#93;_ &#91;) = exp(&#93; _&#91;µ&#93;_ _&#91;r&#93;_ &#91; +&#93; _&#91; α&#93;_ _i_ _&#91;r&#93;_



_j_ _&#91;r&#93;_ &#91;+ (&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;r&#93;_



_i_ _&#91;r&#93;_ &#91;+&#93; _&#91; β&#93;_ _&#91;r&#93;_




_&#91;r&#93;_ _ij_ &#91;)&#93; _&#91;,&#93;_ (7)



_t_ _&#91;mid&#93;_




_&#91;mid&#93;_ _ij_ = exp( _θ_ _ij_ _&#91;mid&#93;_



_ij_ _&#91;mid&#93;_ ) = exp( _µ_ _&#91;mid&#93;_ + _α_ _i_ _&#91;mid&#93;_



_i_ _&#91;mid&#93;_ + _β_ _&#91;mid&#93;_



_j_ _&#91;mid&#93;_ + ( _α · β_ ) _&#91;mid&#93;_ _ij_



_ij_ ) _._ (8)



314 Interpretation of the terms in these formulae is analogous to the one in (6).
315 For the measurement noise level we use the Half-Normal prior


_σ_ _∼_ HalfNormal(0 _,_ 2) _._


316 As the measurement errors _ε_ _ijk_ ’s are assumed to be additive and independent Gaussian, this leads to the
317 observation equation


_y_ _ijk_ = _M_ ( _t_ _k_ ; _θ_ _ij_ ) + _ε_ _ijk_ = _M_ _ijk_ + _ε_ _ijk_ _,_ _ε_ _ijk_ _∼_ _N_ (0 _, σ_ ) _._ (9)


8


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318 Thus for a genotype _i_ and a trial _j_, the _y_ _ijk_ ’s are the longitudinal growth data. The model in (6), (7), (8)
319 and (9) is a GLMM with a non-standard link function for each of the DE parameters. The non-standard
320 link follows from a composition of the exponential function and the ODE solution (log-logistic function).
321 Normality of measurement errors is a reasonable assumption as a first approximation in the present setting.
322 In fact, daily APSIM wheat data were generated without noise, and therefore the unexplained residual
323 variation can be expected to be relatively small. The error standard deviation _σ_ quantifies the lack of fit
324 of the present model. The wide spacing of the data in time is expected to mitigate correlations between
325 residuals. See also Section 2.2 in Seber and Wild (1989).
326 Priors in Bayesian analyses can be set based on the experience of the user, knowledge of the problem at
327 hand, convenience, and regularization or numerical stability considerations. For data from plant breeding
328 experiments, the variation between trials is typically much larger than that between genotypes, while
329 _G × E_ is again smaller than variation between genotypes. We did not implement that knowledge in
330 the current analyses and used only weakly informative priors for our DE parameters, because we knew
331 that the data would be highly informative, while the prior effects would be limited. Nowadays, many
332 Bayesians are comfortable with using data-dependent priors; see, e.g., Section 9.5 in Gelman et al. (2021)
333 for the rationale behind default priors in the popular **R** package **rstanarm**, which is similar to the
334 **brms** procedure we used for our analyses in this paper, and cf. Gelman et al. (2017). The abundance of
335 data (specifically, the data for genotypes outside our subset of 48 genotypes) in our case offered some
336 possibilities for fine-tuning and experimentation with priors: for instance, we inspected where the observed
337 growth curves level off and centered the priors so that this range receives substantial prior mass. As a
338 qualification, we remark that we aimed at investigating dynamic phenotypes at medium-time resolution,
339 i.e., biweekly, as can occur in experiments with regular drone flights. The number of observations per
340 growing season for such experiments is maximally around 10 to 15. This number restricts the complexity
341 of the DE system that can be successfully fitted to such data.


342 **2.6** **Parameter** **identifiability**



Although in Section 2.5 the logarithms of the parameters of the differential equation, i.e. _θ_ _&#91;M&#93;_



_ij_ _&#91;r&#93;_ &#91;and&#93; _&#91; θ&#93;_ _ij_ _&#91;tmid&#93;_



_ij_ _&#91;, θ&#93;_ _&#91;r&#93;_



343 _ij_ _ij_ _ij_ _,_
344 are identifiable, their additive decompositions into the sums of the main genotypic and environmental
345 effects and their interactions are not unique. This is well-known for ANOVA-type models. Additional
346 restrictions must be imposed to talk about genotypic, environmental, and _G × E_ effects. Thus, once
347 the MCMC samples of the parameters have been collected, in the post-processing step we applied the

348 sum-to-zero restrictions on _α_ _i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ _j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;p&#93;_ _ij_ _&#91;,&#93;_ &#91;with&#93; _&#91;p&#93;_ &#91;being&#93; &#91;one&#93; &#91;of&#93; _&#91;M&#93;_ &#91;,&#93; _&#91;t&#93;_ _&#91;mid&#93;_ &#91;and&#93; _&#91;r.&#93;_ &#91;See,&#93; &#91;e.g.,&#93; &#91;Kruschke&#93;
349 (2014), Section 20.1.1, Gelman and Hill (2006), Section 19.4, and Ogle and Barber (2020) for details. Main
350 effects and interactions refer to parameters in this new parametrization, and are unambiguously defined.

351 In principle, the new parameters need to receive other names, such as _α_ ˜︁ _i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ &#91;˜︁&#93; _j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _α_ &#91; ˜︃&#93; _· β_ ) _&#91;p&#93;_ _ij_ _&#91;.&#93;_ &#91;However,&#93; &#91;for&#93;



_i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ _&#91;p&#93;_



_j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;p&#93;_



_j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _α_ &#91; ˜︃&#93; _· β_ ) _&#91;p&#93;_



_i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ &#91;˜︁&#93; _j_ _&#91;p&#93;_



351 In principle, the new parameters need to receive other names, such as _α_ ˜︁ _i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ _j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _α · β_ ) _&#91;p&#93;_ _ij_ _&#91;.&#93;_ &#91;However,&#93; &#91;for&#93;

352 notational simplicity, in the rest of the paper we will keep the old notation _α_ _i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ _j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;p&#93;_ _ij_ _&#91;,&#93;_ &#91;but&#93; &#91;we&#93;
353 will mean the parameters in the new parameterization. We also remark that priors in Bayesian mixed
354 models help with weak identifiability of parameters. In fact, the conclusions in this paper would have
355 stayed largely unchanged, had we used in our analysis the raw random effects instead of the adjusted ones.



_i_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;β&#93;_ _&#91;p&#93;_



_j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;p&#93;_



356 **2.7** **Interpretation** **of** **genotypic,** **environmental** **and** _G × E_ **parameters**



357 Interpretations of dynamic behavior shown by individual genotypes and induced by individual envi358 ronments can be based on estimates for individual effects and their dispersion parameters building on
359 the interpretation of similar parameters in traditional quantitative genetic models for continuous traits.
360 To be more specific, we will build such interpretations on the posterior distributions for genotypic and

361 environmental main effects and _G × E_ effects, i.e., _α_ _i_ _&#91;p&#93;_ &#91;,&#93; _&#91;β&#93;_ _j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;p&#93;_ _ij_ &#91;,&#93; &#91;respectively,&#93; &#91;with&#93; _&#91;p&#93;_ &#91;being&#93; &#91;one&#93; &#91;of&#93;

362 _M_, _t_ _&#91;mid&#93;_ and _r_, together with the corresponding dispersion parameters _σ_ _α_ _&#91;p&#93;_ &#91;,&#93; _&#91;σ&#93;_ _β_ _&#91;p&#93;_ &#91;,&#93; &#91;and&#93; _&#91;σ&#93;_ ( _&#91;p&#93;_ _α.β_ ) &#91;.&#93; &#91;Inspection&#93; &#91;of&#93;
363 the posterior distributions of the dispersion parameters will inform us about the relative importance of
364 genotypic and environmental main effects as well as that of _G × E_ . To appreciate the relative magnitudes
365 of _G × E_ effects versus genotypic main effects for the dynamic parameters, we will look at the posteriors
366 for the ratios of the _G × E_ standard deviations to the standard deviations for genotypic main effects.

367 For dynamic parameters with sizeable dispersion for _G × E_, individual interaction effects, ( _α · β_ ) _&#91;p&#93;_ _ij_ &#91;,&#93;
368 can be studied via their credible intervals to verify whether they contain zero. Questions concerning
369 genotypic and environmental characterizations can be addressed by counts on non-null _G × E_ effects.
370 Genotypes can be characterized on the percentage of times they show non-null _G × E_ effects across all
371 trials or subsets of trials. This percentage can be interpreted as a measure of stability. The four locations



_i_ _&#91;p&#93;_ &#91;,&#93; _&#91;β&#93;_ _&#91;p&#93;_



_j_ _&#91;p&#93;_ &#91;and&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;p&#93;_



_α_ _&#91;p&#93;_ &#91;,&#93; _&#91;σ&#93;_ _&#91;p&#93;_




_&#91;p&#93;_ &#91;and&#93; _&#91;σ&#93;_ _&#91;p&#93;_

_β_ &#91;,&#93; (



9


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.



372 that were included in the simulation data represent different growing regions within Australia. Therefore,
373 it may be of interest to see to which extent the incidence of non-null _G × E_ effects differs between those
374 regions. A low incidence may point to a non-discriminative environment, whereas a high incidence would
375 point to a discriminative environment.
376 Posterior distributions of environmental and/or _G × E_ effects can be used for environmental character377 ization to create so-called environmental scenarios or envirotypes (Xu, 2016; Resende et al., 2021; Chen
378 et al., 2026; Fernandez et al., 2026). Typically in environmental characterization, trials are clustered into
379 groups, with the groups representing a distinguishable type of growing environment. Envirotypes can
380 serve to develop more efficient breeding strategies. We illustrate how to use posterior medians for the

381 environmental main effect parameters _β_ _j_ _&#91;M&#93;_ &#91;,&#93; _&#91;β&#93;_ _j_ _&#91;mid&#93;_, and _β_ _j_ _&#91;r&#93;_ &#91;as&#93; &#91;inputs&#93; &#91;for&#93; &#91;an&#93; &#91;environmental&#93; &#91;characterization.&#93;
382 These posterior medians were standardized and collected in a vector of length three. These vectors were
383 clustered into three groups using a _K_ -means algorithm (MacQueen, 1967). Choosing three or four clusters
384 is supported by relevant literature on envirotypes (Fernandez et al., 2026). The results of the _K_ -means
385 clustering depend on the random initialization of the algorithm. With three groups, the inferred clusters
386 were stable over multiple runs of the algorithm.
387 For plotting purposes, we used for some figures medoid representations (Van der Laan et al., 2003). For
388 environments, this resulted in real environments that were at the center of the space spanned by estimates
389 for the environmental main effects in the GLMMs for the three parameters. The medoid environment can
390 then be thought of as a typical environment within a class of environments. The same technique was also
391 used for plotting genotypic information.



_j_ _&#91;M&#93;_ &#91;,&#93; _&#91;β&#93;_ _j_ _&#91;mid&#93;_



_j_, and _β_ _j_ _&#91;r&#93;_



392 **2.8** **Software** **implementation**


393 We implemented our Bayesian approach in **Stan**, specifically using the **R** package **brms** . **Stan** is a
394 state-of-the-art platform for statistical modeling and high-performance statistical computation. The
395 principal engine to perform Bayesian inference in **Stan** is the No-U-Turn-Sampler (NUTS), a cutting-edge
396 variant of the Hamiltonian Monte Carlo (Hoffman and Gelman, 2014; Betancourt, 2017; Betancourt
397 et al., 2017). The **R** package **brms** uses **Stan** as its backend, but employs the formula syntax similar
398 to the popular **lme4** package. This results in a familiar and simple interface for performing regression
399 type analyses. See B¨urkner (2017, 2018, 2021) for additional information. For a general overview and
400 comparison of the modern software for Bayesian inference, see Strumbelj &#91;ˇ&#93; et al. (2024).
401 **brms** automatically evaluates the popular _R_ &#91;ˆ&#93; convergence diagnostic for Markov chains it generates
402 (Gelman and Rubin, 1992; Vehtari et al., 2021), and issues a warning when its values are above the
403 commonly used threshold 1 _._ 05 _._ See also Table 5 in the Supplementary Material for values of _R_ &#91;ˆ&#93;, which are
404 all below the threshold 1.05. In order to verify convergence, we also visually examined the trace plots
405 and autocorrelation functions for our Markov chains to the extent that this is possible given the large
406 number of parameters in the model (Gabry et al., 2025). The plots for an arbitrary selection of the model
407 parameters are presented in the Supplementary Material in Figures 11 and 12. From Table 5 we also see
408 that the lowest effective sample sizes occur for the global intercept parameters, which are weakly identified
409 from the data and are not of inferential interest. On the other hand, the standard deviation parameters
410 have bulk and tail effective sample sizes above 400 _,_ which allows for accurate simulation-based inference
411 in the present context.
412 To handle the **brms** output, we mainly employed the **R** package **tidybayes** (Kay, 2022), and other
413 capabilities offered by **R** (R Core Team, 2022). For plotting in **R** we relied on **ggplot2** (Wickham, 2016),
414 as well as several other packages building upon and extending **ggplot2** .
415 In our implementation in **brms**, we used an explicit form of the log-logistic function given in (4) .
416 For future extensions, we note that availability of an analytic solution to a differential equation is not
417 a requirement for our Bayesian approach: it also works when the analytic solution is replaced with a
418 numerical solution. In that case, instead of **brms**, the model may be implemented directly in **Stan** ; cf.
419 Chatzilena et al. (2019) and Grinsztajn et al. (2021). Alternatively, additional **Stan** code can be injected
420 into the **brms** model specification. Fitting, however, is faster with an analytic solution. As for the
421 effect of the approximation error on posterior inference resulting from numerical integration, the impact
422 stays bounded, and is negligible when the step size of the ODE solver is chosen to be small enough; see
423 Donnet and Samson (2007) for a mathematically precise statement. **Stan** implements a number of reliable
424 adaptive ODE solvers (Stan Development Team, 2023, Chapter 13). For early contributions to Bayesian
425 fitting of hierarchical differential equation models, see Bois et al. (1996); Gelman et al. (1996); Wakefield
426 (1996). These early contributions rely on Gibbs sampling (Geman and Geman, 1984; Gelfand and Smith,
427 1990). However, the Gibbs sampler is known to suffer from poor mixing in statistical problems with


10


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428 highly correlated parameters in the posterior (De Jong and Shephard, 1995; Lindsten and Sch¨on, 2013).
429 This is inherent in the sampler because of its sequential updating of single individual parameters in any
430 given iteration. This slow convergence hampers the scalability of the Gibbs sampler to high-dimensional
431 models with complex posterior geometry, such as those defined by differential equations (Girolami, 2008;
432 Calderhead and Girolami, 2009), and especially their hierarchical extensions.

## 433 3 Results


434 **3.1** **Goodness** **of** **fit** **and** **characterization** **of** **sources** **of** **variation**


435 To assess how well our model fitted the ‘observed’ longitudinal data for individual genotypes in individual
436 environments, we looked at plots of observed (Figure 2) and fitted (Figure 3) data. The observations were
437 created by sampling at medium-time resolution biomass data from APSIM wheat simulations. There were
438 four locations with 31 years of trials, in total 124 environments, for a set of 48 genotypes. In Figure 2, for
439 each location we present the so-called medoid trial, a trial that can be thought of as best representing the
440 group (location) to which it belongs. For such a medoid trial, we show the daily data for all genotypes.
441 The colors of the genotypes are consistent in Figures 2 and 3. Moreover, to give an idea of the amount
442 of uncertainty in the obtained fits, in Figure 4 we show 95% Bayesian pointwise prediction bands for
443 the medoid genotype in the medoid year (trial) at each of the 4 locations. As can be readily seen, most
444 observations fall within the prediction bands.
445 The log-logistic fits were good in that they follow the observed data closely for all genotypes and trials,
446 and for most predictive purposes in this setup the log-logistic fits are probably good enough. Still, the
447 observed data contain small bumps, deviations from the smooth log-logistic fits, which are very likely
448 caused by short-term meteorological events, such as elevated temperatures and drought. Such bumps
449 cannot be incorporated into the log-logistic model, but can show up in residual plots, see Figure 13.
450 Figure 2 contains genotypic curves that hardly intersect, but there are clear differences between
451 locations, between years within locations (trials) and between genotypes. Narrabri and Yanco attained
452 higher biomasses than Merredin and Emerald, with Emerald having the lowest biomasses. The amount of
453 variation between years within locations seems comparable across the four locations, see Figure 5.
454 Inspection of the posterior standard deviations for environmental and genotypic main effects and
455 _G × E_ effects in Figure 6 shows that the dynamic parameters for asymptote, midpoint and slope follow
456 the standard partitioning of phenotypic variation with environmental main effects being responsible for
457 the majority of the phenotypic variation, followed by genotypic main effects and finally _G × E_ effects.
458 The greatest variation was found in the asymptote, followed by the midpoint, while the slope was clearly
459 less variable in this wheat panel. _G × E_ variation is best appreciated in relation to genotypic main effect
460 variation. Figure 7 presents ratios of _G × E_ standard deviation to genotype standard deviation. For the
461 asymptote, this ratio was between 0 _._ 6 and 0 _._ 9 _,_ while for the midpoint it was between 0 _._ 25 and 0 _._ 35 _._ For
462 the slope, the same ratio had a value between 0 _._ 0 and 0 _._ 1 _._ The _G × E_ appeared clearly for the asymptote,
463 but for the midpoint and slope parameter it had little to no influence. Therefore, the rough biomass
464 growing pattern for wheat seems predictable from additive GLMMs for at least midpoint and slope. That
465 is, no or hardly any _G × E_ plays a role for midpoint and slope parameters in the biomass growth functions.
466 For the asymptote, the maximum biomass, _G × E_ does play a role, and further study is required to find
467 out how to arrive at a predictive model for biomass taking into account the _G × E_ for maximum biomass.


468 **3.2** _G × E_ **interactions**



469 Interactions can be further studied via credible intervals for interaction terms ( _α · β_ ) _&#91;p&#93;_ _ij_ &#91;,&#93; &#91;and&#93; &#91;verifying&#93;
470 whether zero is contained within these intervals or not. Table 2 summarizes the results and confirms the
471 impression that with the log-logistic model, most of the interaction is to be discovered for the asymptote,

472 _M_ _ij_ _&#91;max&#93;_ . For this DE parameter, _G × E_ did occur in about a third of all _G × E_ combinations across the full
473 set of trials. More detail is provided by the number or percentage of _G × E_ interactions per location in

474 Table 3. For parameters _M_ _ij_ _&#91;max&#93;_, there is some variation between locations in the frequencies of interactions,
475 with _G × E_ being more frequent in Yanco and less frequent in Merredin. Further zooming on _G × E_
476 interactions, we inspect the non-zero interactions in the trials over time (years) for each of the locations.
477 In Figure 8, we again see that Yanco in general induces more _G × E_ than the other three locations, with
478 Merredin inducing the lowest frequency of _G × E_ . We also see that there is a lot of variation in the
479 frequency of non-null _G × E_ between years within locations.


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_&#91;M&#93;_ _ij_ &#91;,&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;mid&#93;_ _ij_



Table 2: Frequencies of credible intervals for interaction terms ( _α · β_ ) _&#91;M&#93;_



_ij_ and ( _α · β_ ) _&#91;r&#93;_



Table 2: Frequencies of credible intervals for interaction terms ( _α · β_ ) _ij_ &#91;,&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _ij_ and ( _α · β_ ) _&#91;r&#93;_ _ij_ &#91;that&#93;

exclude zero, i.e., that do indicate _G × E_ .




_&#91;M&#93;_ _ij_ **(** _α · β_ ) _&#91;mid&#93;_ _ij_



**(** _α · β_ ) _&#91;M&#93;_ _ij_



_ij_ **(** _α · β_ ) _&#91;r&#93;_ _ij_



_ij_



Credible interval excludes zero 2173 91 0
Percentage of intervals without zero 36 _._ 5% 1 _._ 5% 0%




_&#91;M&#93;_ _ij_ &#91;,&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _&#91;mid&#93;_ _ij_



Table 3: Frequencies of credible intervals for interaction terms ( _α · β_ ) _&#91;M&#93;_



_ij_ and ( _α · β_ ) _&#91;r&#93;_



Table 3: Frequencies of credible intervals for interaction terms ( _α · β_ ) _ij_ &#91;,&#93; &#91;(&#93; _&#91;α&#93;&#91; ·&#93;&#91; β&#93;_ &#91;)&#93; _ij_ and ( _α · β_ ) _&#91;r&#93;_ _ij_ &#91;that&#93;

exclude zero, i.e., that do indicate _G × E_ . Frequencies are grouped by location.




_&#91;M&#93;_ _ij_ **(** _α · β_ ) _&#91;mid&#93;_ _ij_



_ij_



**(** _α · β_ ) _&#91;M&#93;_ _ij_



_ij_ **(** _α · β_ ) _&#91;r&#93;_ _ij_



Emerald 534 0 0

Merredin 422 15 0

Narrabri 586 41 0

Yanco 631 35 0


Total 2173 91 0


480 When we apply the same logic to the genotypes, we can compare genotypes for the number of non-null
481 _G × E_ effects across trials. We can interpret this number as an indicator for the genotypic stability of DE
482 parameters. The lower the frequency or number of non-null interactions, the higher the stability of the
483 genotype. Figure 9 offers a view on substantial genotypic variation for non-zero interactions for _G × E_ in

484 the asymptote, ( _α · β_ ) _&#91;M&#93;_ _ij_ &#91;.&#93;


485 **3.3** **Environmental** **characterization**



486 The parameters in the GLMMs for the DE parameters can be used to characterize genotypes and

487 environments. For the environments, the environmental main effect parameters _β_ _j_ _&#91;M&#93;_ &#91;,&#93; _&#91;β&#93;_ _j_ _&#91;mid&#93;_, and _β_ _j_ _&#91;r&#93;_ &#91;should&#93;
488 reflect the local growing conditions in ways comparable to physical and physiological measurements. Upon
489 collecting these parameters in three-dimensional vectors, we used the _K_ -means clustering algorithm on
490 these environmental descriptors. The _K_ -means solution was stable for solutions with three clusters over
491 multiple runs with different initializations. On inspection of these clusters, it turned out that Emerald
492 and Merredin trials each dominated one cluster, while a third cluster was a combination of especially
493 Narrabri and to a lesser extent Yanco trials. Envirotypes facilitate the efficient modeling of _G × E_ by
494 partitioning the initial _G × E_ in a part explained by _G × Envirotype_ interaction and a residual part. For
495 the APSIM wheat data here, because the envirotypes were dominated by differences between locations, a
496 description of _G × E_ for the asymptote by introducing a _G × Envirotype_ term was about as effective as
497 introducing a _G × Location_ term, and a comparable residual _G × E_ remained.



_j_ _&#91;M&#93;_ &#91;,&#93; _&#91;β&#93;_ _j_ _&#91;mid&#93;_



_j_, and _β_ _j_ _&#91;r&#93;_



498 **3.4** **Genotypic** **characterization**



499 In Bustos-Korts et al. (2019b), genotype-specific values for a panel of 199 genotypes were generated for 12
500 APSIM parameters that determine phenology, capture of environmental resources, resource use efficiency,
501 and biomass partitioning. APSIM parameters were created from a genetic basis consisting of 300 QTLs
502 whose effects were sampled from gamma distributions with parameters following estimates obtained from
503 analysing real wheat data.
504 We wanted to characterize the genotypes in our hierarchical analysis by the estimated genotypic
505 main effects in the GLMMs for the DE parameters. To this end, we compared the estimates for these
506 genotypic effects with APSIM parameters used to generate the data by Bustos-Korts et al. (2019b).
507 APSIM parameters that changed over time were not taken into account. The selected APSIM parameters
508 are summarized in Table 4, which is constructed as a subset of Table 2 in Bustos-Korts et al. (2019b).

509 We computed correlations between each of the DE parameter _α_ _i_ _&#91;M&#93;_ _&#91;, α&#93;_ _i_ _&#91;mid&#93;_ and _α_ _i_ _&#91;r&#93;_ &#91;(estimated by posterior&#93;
510 medians) on the one hand, and the individual APSIM parameters, on the other. We also obtained the
511 asymptotic 95% confidence intervals based on the Fisher z-transformation using the standard **R** command
512 **cor.test** . The results are presented graphically in Figure 10.
513 Several APSIM parameters show significant correlations with the inferred parameters of our Bayesian
514 hierarchical model. The maximum biomass seems to be strongly negatively related to the lower limit
515 for water uptake ( `ll` ~~`m`~~ `odifier` ), whereas that relationship is positive for the slope parameter. Higher



_i_ _&#91;M&#93;_ _&#91;, α&#93;_ _i_ _&#91;mid&#93;_



_i_ and _α_ _i_ _&#91;r&#93;_



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Table 4: Genotype-specific parameters from APSIM that were used in this study for comparison purposes.


**Parameter** **APSIM** **name** **Unit**


Fr. of leaves senescing main stem node `fr` ~~`l`~~ `f` ~~`s`~~ `en` ~~`r`~~ `ate` &#91; &#93;
Grains/gram of stem at flowering `grains` ~~`p`~~ `er` ~~`g`~~ `ram` ~~`s`~~ `tem` grains _g_ _stem_ _&#91;−&#93;_ &#91;1&#93;

Lower limit for water uptake `ll` ~~`m`~~ `odifier` &#91; &#93;
Maximum grain size `max` `grain` ~~`s`~~ `ize` mg
Sensitivity to photoperiod `photop` ~~`s`~~ `ens` &#91; &#93;
Potential grain filling rate `potential` ~~`g`~~ `rain` ~~`f`~~ `illing` ~~`r`~~ `ate` g grain _&#91;−&#93;_ &#91;1&#93; day _&#91;−&#93;_ &#91;1&#93;

Thermal time to reach floral initiation `tt` ~~`f`~~ `loral` ~~`i`~~ `nitiation` _◦_ C d
Sensitivity to vernalization `vern` `sens` &#91; &#93;


516 slopes were associated with larger thermal times till floral initiation ( `tt` ~~`f`~~ `loral` ~~`i`~~ `nitiation` ) and stronger
517 photoperiod sensitivity ( `photop` ~~`s`~~ `ens` ). The midpoint time did not show any obvious correlation with
518 APSIM parameters.

## 519 4 Discussion


520 **4.1** **Incorporating** **phenotyping** **information** **into** **mixed** **models** **for** **genomic**
521 **prediction**


522 In recent years, automatic monitoring of longitudinal phenotyping data has become an integral part of
523 many plant breeding programs and experiments. Incorporating this kind of information into breeding
524 strategies and decisions is a topic of current research. From a prediction perspective, genomic prediction
525 models can be improved by combining genomic and phenotyping data into genotype-to-phenotype models.
526 An important objective of such integrated models is to increase the predictive ability of within-trial
527 phenotypes at later time points from genomic information and phenotyping information at earlier time
528 points. In other words, the target phenotypes, such as yield, phenological traits, and yield components,
529 are forecasted from early season information. The chosen modeling framework is often that of multi-trait
530 mixed models and random regressions (Baba et al., 2020; Campbell et al., 2018; Momen et al., 2019; Sun
531 et al., 2017, 2019). These models can contain complex formulations for the variance-covariance structures
532 dealing with the correlations between traits over time and the incorporation of one or more kernels on the
533 genotypes to represent genomic relations, but they do not include explicit model terms or structures that
534 represent physiological mechanisms or insights. Furthermore, the above papers leave open how genomic
535 and phenotyping information should be combined to predict yield in future environments under _G × E_ .
536 Jarqu´ın et al. (2014) presented a mixed model framework for genomic prediction between trials in the
537 presence of _G_ _×_ _E_ based on the definition of kernels (relationship matrices) for genotypes and environments.
538 A generalization of this approach addresses _G × E_ while integrating genomic and phenotyping information
539 on genotypes with enviromic information on environments (Adak et al., 2023; Robert et al., 2022).
540 Although the emphasis for this new type of integrated mixed models is on between-trial prediction in
541 place of within-trial prediction, the representation of the additional phenotyping information inside the
542 prediction models ignores most of the physiological principles that make yield the outcome of growth
543 and developmental processes. In this approach, the dynamic environmental inputs that are typical for
544 physiological models are not used. The totality of the physiological information is reduced to a relationship
545 matrix between genotypes.


**–**
546 **4.2** **Crop** **growth** **model** **whole** **genome** **prediction**


547 In stark contrast to the mixed models above that incorporated phenotyping information without reference
548 to physiological models, an alternative approach, called crop growth model - whole genome prediction,
549 builds on elaborate physiological models for prediction in the expectation that such an approach will lead
550 to better between-trial predictions of yield under _G × E_ (Technow et al., 2015; Messina et al., 2018). The
551 CGM-WGP approach predicts the end-point trait yield together with dynamical yield components for
552 new genotypes and environments using marker profiles and dynamic environmental data as inputs. The
553 marker profiles serve to provide a molecular basis to a limited number of physiological traits. Marker
554 effects are estimated following a Bayesian procedure. The CGM-WGP represents a powerful, general and
555 attractive predictive framework founded on prior physiological knowledge. In its initial formulations, the


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556 CGM-WGP approach does not use dynamic observations on plant growth during the season and has to
557 rely fully on the correctness of the pre-specified parameters and relations inside the crop growth model
558 that converts marker profiles and environmental inputs into yield outputs.
559 Crop growth models tend to have many parameters and it is impossible to estimate all of the parameters
560 in crop growth models at a genotype-specific level. When using a CGM-WGP approach, a decision has to
561 be made about which parameters to allow to vary with genotype and which to fix for the crop species as a
562 whole. In the CGM-WGP papers by Technow et al. (2015), Cooper et al. (2016), Messina et al. (2018)
563 and Jighly et al. (2023) only a few yield components are genotype specific and a function of marker inputs.
564 Although the CGM-WGP approach is dynamic for the inputs from the environment and the outputs of
565 the yield components, it does not use dynamic inputs from phenotyping and phenomic devices. Such
566 inputs may contain important information on the occurrence of biotic and abiotic stresses.


567 **4.3** **Our** **hierarchical** **dynamic** **model** **proposal** **to** **function-valued** **modeling** **of**
568 **longitudinal** **traits** **in** **multiple** **trials**


569 The Bayesian framework we developed in this paper provides a flexible framework to model a longitudinal
570 trait for a set of genotypes across multiple environments, taking into account _G × E_ . Our approach is
571 unique because it fits the growth curves simultaneously for all included genotypes and environments.
572 Therefore, propagation of errors and tests about differences between growth trajectories can be performed
573 within a well-defined context, namely that of the Bayesian framework that relies for inference on the
574 properties of the posterior distribution. The same framework contains the tools for constructing prediction
575 intervals along the fitted growth trajectories. Each trajectory is determined by a limited number of
576 biologically interpretable DE parameters whose expectation is itself a GLMM with main effects for
577 genotype and environment, as well as _G × E_ .
578 In our approach, we followed a function-valued trait modeling perspective to growth trajectories as
579 propagated by Wang et al. (2014), Gomulkiewicz et al. (2018) and Baker and Wang (2021). Within that
580 framework, we interpret the DE parameters as phenotypic traits themselves, as traits underlying the
581 dynamics of the yield component or secondary trait that we are studying. Analogously to a quantification
582 of the sources of variation in the context of linear mixed models in quantitative genetics, the contributions
583 of genotype, environment, and _G × E_ to the total ’phenotypic variation’ for the DE parameter can be
584 assessed within the Bayesian framework by inspecting the posterior distributions for the corresponding
585 dispersion parameters. Their magnitudes reflect their relative importance. For classical phenotypes such
586 as yield, biomass and phenology, the environment is by far the most important source of variation, usually
587 followed by the genotype when the environmental conditions are not too wildly different between trials
588 and finally the _G × E_ . Exactly that order of importance also occurred for the DE parameters in our
589 model for biomass, for all three the DE parameters of asymptote, midpoint, and slope. Comparison of
590 dispersion parameters between the three DE parameters identified the asymptote as the parameter with
591 the strongest _G × E_, that is, with the highest ratio of _G × E_ to genotype variation. For the midpoint and
592 slope, _G × E_ was small to absent, which means that the dynamics of biomass followed an additive model
593 for these two parameters.


594 **4.4** **Alternative** **function-valued** **modeling** **approaches** **for** **longitudinal** **traits**


595 A function-valued approach to plant growth for populations of genotypes was also proposed by Baker et al.
596 (2018a,b). For leaf width and length in _Brassica_ _rapa_, logistic models were fitted on growing degree days
597 per plant. The growth parameters were then extracted and subsequently further analyzed in a Bayesian
598 hierarchical analysis of variance (ANOVA) model containing a population, genotypic and plant level.
599 Both Baker et al. (2018a) and Baker et al. (2018b) tested plant growth under two plant densities that
600 were interpreted as different environmental conditions. A test for genotype by density interactions was
601 performed and on failure to reject the null hypothesis of no interaction, it was concluded that the growth
602 of a genotype as modeled under one density could be used to predict the growth of the same genotype
603 under an alternative density. In our approach, in contrast to Baker et al. (2018a) and Baker et al. (2018b),
604 a single inferential framework was used for both modeling the dynamics of plant growth and expressing
605 the dynamic parameters in terms of genotype, environment, and _G × E_ . A test of _G × E_ for individual DE
606 parameters followed straightforwardly from inspection of the posterior for the corresponding dispersion
607 parameter.
608 Baker et al. (2018a) extended their Bayesian ANOVA model for the logistic parameters by making the
609 genotypic means for these parameters dependent on photosynthetic capacity. In this way, they wanted


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610 to test whether carbon limitations were responsible for genotypic differences as a factor affecting the
611 growth dynamics of individual genotypes. The photosynthetic capacity can be measured in different
612 ways, some of them being very time consuming others delivering approximations via remote sensing. The
613 insertion of approximate physiological parameters from phenotyping devices or phenomic measurements
614 to describe variation in growth parameters offers an attractive and powerful modeling perspective. Similar
615 tests for DE parameters being a function of certain genotype-dependent limitations or capacities can
616 naturally be implemented in our framework by introducing genotypic covariates into the GLMMs for the
617 DE parameters and inspecting the posterior distribution for the slope with respect to such a covariable.
618 Baker et al. (2018b) identified quantitative trait loci (QTLs) for dynamic parameters, after estimation
619 of those dynamic parameters in logistic growth models. They follow up by creating QTL-based predictions
620 for the full growth trajectories. Again, this is a multi-step approach. Within our Bayesian hierarchical
621 model for plant growth, we can in principle directly predict the dynamical response from marker profiles
622 by replacing the genotypic main effects in the GLMMs for the growth parameters by penalized regressions
623 on marker profiles. With a double exponential prior on the marker effects this would lead to QTL mapping
624 via LASSO (Least Absolute Shrinkage and Selection Operator) regression (Li and Sillanp¨a¨a, 2012), while
625 with a normal prior we would arrive at genomic prediction using a ridge regression.
626 In the field of animal breeding, Varona et al. (1999) use the Gibbs sampler (or, rather, the Metropolis627 within-Gibbs sampler) with an explicit form of the growth curve, specifically the Von Bertalanffy growth
628 curve, within the mixed effects modelling framework. Their approach is not generalisable to the differential
629 equation models that do not admit explicit solution. The Gibbs sampler also does not scale well in such
630 complex nonlinear models. In fact, Onogi et al. (2019), who use a similar computational approach as
631 Varona et al. (1999), are constrained to run their Gibbs sampler for millions of iterations (Onogi et al.,
632 2019, p. 5). This is indicative of slow mixing of the sampler. In contrast, in order to efficiently explore the
633 posterior distribution, a few thousand iterations typically suffice with the NUTS sampler (Hoffman and
634 Gelman, 2014; Betancourt, 2017; Betancourt et al., 2017), which is the computational algorithm of **brms** .
635 The mathematical model in Onogi (2020) is similar to that in Varona et al. (1999); Onogi et al. (2019)
636 and does not envision a governing differential equation without a closed-form solution. The computational
637 approach they use is a hybrid method from Onogi et al. (2015). This combines Gibbs sampling with
638 coordinate ascent variational inference (CAVI). However, even though in general faster than MCMC
639 sampling, CAVI is closely related to Gibbs sampling and suffers from the same general drawbacks (Blei
640 et al., 2017). A computational bottleneck of the Bayesian approach to inference in DE models lies in the
641 need for their repeated numerical integration in likelihood evaluations. Already for a medium complexity
642 model, this is not realistically feasible when the computational method requires millions of iterations
643 until convergence (Voit and Almeida, 2004, Appendix 1). Note also that while the MCMC methods are
644 guaranteed (under idealised conditions) to recover the posterior distribution as the number of iterations
645 grows indefinitely (Roberts and Rosenthal, 2004), this is not the case with variational inference, which
646 involves a non-vanishing approximation error even in the limit.


647 **4.5** **Outlook**


648 The current version of our hierarchical Bayesian model for longitudinal traits in multiple trials is promising
649 as a starting point for a framework for the prediction of yield under _G × E_ . However, a number of issues
650 require attention. First of all, from the candidate DE models described in Van Voorn et al. (2023) we
651 chose for this paper the simplest one, the logistic model, which was slightly modified, for computational
652 reasons, into a log-logistic model. The log-logistic model does not contain an environmental driver, as in
653 the irradiance model or the temperature model of Van Voorn et al. (2023). Neither does the log-logistic
654 model contain an environmental state variable, as in the water model of Van Voorn et al. (2023). The
655 log-logistic model has an explicit solution that turns our hierarchical dynamic model into a hierarchical
656 regression model. Therefore, estimation procedures are obviously easier to perform. Nevertheless, the
657 strong point of our approach remains that parameters for growth processes can explicitly be modeled as
658 functions of genotypic, environment and _G×E_ terms. The usefulness of parameters of yield components for
659 incorporation into predictive models for yield will firstly depend on the extent to which these parameters
660 are free of _G × E_ . Even when parameters for yield components do show _G × E_, they can still be useful for
661 yield prediction as long as the _G × E_ can be modeled in terms of environmental covariables, that is, the
662 _G × E_ term for the rate parameter is written as the product of a genotypic sensitivity times a predictable
663 environmental condition. The situation here is comparable to the use of factorial regression in models for
664 _G × E_ in target traits (Van Eeuwijk et al., 2016; Avagyan et al., 2025).
665 When our DE system does not have an explicit analytical solution, our hierarchical Bayesian framework


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666 will have to solve the DE system for each combination of genotype and environment numerically together
667 with estimating the GLMM parameters for the DE parameters. This is possible within our modeling
668 framework that relies on the Bayesian modeling language **Stan** and we will present results in follow-up
669 papers. Computing resources will need to be increased when there is no explicit solution for the DE
670 system. For the analyses presented in this paper, we kept the playing field small as the objective was to
671 investigate the principles of a hierarchical Bayesian approach to longitudinal modeling. A first next step
672 will consist of upscaling our modeling facilities to medium sized panels of genotypes (100s) and sets of
673 environments (25–100).
674 An ultimate aim of longitudinal traits modeling in phenotyping experiments is to arrive at a predictive
675 model that allows us to predict yield under _G × E_ . Different DE systems can be tried to see whether
676 formulations can be found in which parameters have no or limited _G × E_ or in which _G × E_ depends on
677 predictable environmental covariables. Further, the genotypic terms, intercepts, and slopes in the GLMMs
678 for the DE parameters should be predictable from marker profiles, like in standard genomic prediction
679 approaches. For the prediction of genotypic intercepts and slopes for DE parameters, an additional
680 layer can be added to the Bayesian hierarchy. An alternative is a two-step approach in which these
681 genotypic intercepts and slopes are predicted in a separate genomic prediction step. An interesting aid in
682 identifying candidate DE systems for modeling longitudinal traits is the SINDy-PI algorithm (Kaheman
683 et al., 2020) that tries to identify sparse representations of dynamic systems. An illustrative application
684 of this approach in the context of genotype-specific crop growth modeling is presented by Verburg et al.
685 (2026). We feel that our hierarchical Bayesian approach to longitudinal trait modeling opens up new
686 perspectives to predict yield under _G × E_ . This approach provides an additional tool for breeders and
687 geneticists in conjunction with the mixed kernel-based models following the strategy outlined by Jarqu´ın
688 et al. (2014) and the CGM-WGP strategy introduced by Technow et al. (2015) and Messina et al. (2018).

## 689 Conflict of interest statement


690 Authors ST, NF, RM and CM were employees of Corteva Agriscience when this manuscript was conceived.
691 The remaining authors declare that the research was conducted in the absence of any commercial or
692 financial relationships that could be construed as a potential conflict of interest.

## 693 Author contributions


694 Modelling **G** _×_ **E** _×_ **M** was conceived between Corteva Agriscience and Wageningen University &amp; Research
695 – Biometris, with groups led by CM and FV, respectively. Conceptualization and development was done
696 by all authors. The APSIM wheat simulation data were created by DB. Model fitting was done by SG.
697 The first version manuscript writing and preparation was done by SG, GV and FV. Intermediate editing
698 of the manuscript was done by all authors. SG, GV, MB and FV did the final manuscript editing. All
699 authors contributed to the article and approved the submitted version.

## 700 Funding


701 This research was supported by Predictive Agriculture, Research &amp; Development at Corteva Agriscience
702 (2019–2020).
703 FV worked on this paper partly in the context of the EU-INVITE project, which is part of the
704 Horizon 2020 Framework Programme of the European Union, under Grant Agreement 817970 ( `&#91;https:&#93;(https://www.h2020-invite.eu/)`
705 `&#91;//www.h2020-invite.eu/&#93;(https://www.h2020-invite.eu/)` ).
706 FV, MB and SC contributed to this paper partly within the framework of the GRDC INVITA UQ-WUR
707 and GRDC AAGI UQ-WUR Collaborative Research Agreements.
708 SG, MB and GV acknowledge funding from the WUR Investment Theme on Data-Driven Discoveries
709 in a Changing Climate (D3-C2).
710 DB contributed to this paper thanks to the funding of Subvenci´on a la Instalaci´on en la Academia,
711 ANID 85220037.


16


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.

## 712 Acknowledgments


713 Acknowledgment is made to the APSIM Initiative, which takes responsibility for quality assurance and a
714 structured innovation program for APSIM’s modelling software, which is provided free for research and
715 development use (see `&#91;https://www.apsim.info/&#93;(https://www.apsim.info/)` for details).

## 716 Data availability statement


717 The APSIM wheat dataset analyzed in this study can be accessed via Bustos-Korts (2023).

## 718 Declaration of AI use


719 Parts of the **R** analysis script were written with the assistance of GitHub Copilot inline code completions
720 in RStudio 2024.12 during 2025. The completions were generated by GitHub’s default completion models
721 at the time: a GPT-3.5 Turbo-based model, GPT-4o Copilot and GPT-4.1 Copilot. The authors reviewed,
722 tested and revised all code suggested by Copilot and verified that the results are accurate and reproducible.
723 Generative AI was not used to design the model, interpret the results, or write the manuscript. AI
724 assistance (Claude Opus 5.5) was utilized during the final preparation of the submission strictly for
725 language enhancement, stylistic refinement, and copy editing.

## 726 Software


727 The computer code used in this paper is available through the dedicated GitHub repository at `&#91;https:&#93;(https://github.com/gugushvili/dynamic_phenotypes)`
728 `&#91;//github.com/gugushvili/dynamic_phenotypes&#93;(https://github.com/gugushvili/dynamic_phenotypes)` .

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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.

## 1057 5 Figures


Figure 1: The Kruschke style diagram for the hierarchical Bayesian model from Section 2.5. See the main
text for the notation. The inner and outer layers actually consist of three identical copies of distributions,
although only one is shown. For each coordinate _θ_ _ij_ _&#91;p&#93;_ &#91;of&#93; &#91;the&#93; &#91;parameter&#93; &#91;vector&#93; _&#91;θ&#93;_ _&#91;ij&#93;_ &#91;,&#93; &#91;with&#93; &#91;the&#93; &#91;superscript&#93;

varying over _p_ = _M_, _mid_ and _r_, a separate distribution is specified. The indices halfway the arrows
indicate the way in which the variables or parameters are replicated over those indices.


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.


Figure 2: Observed daily APSIM wheat biomass data for medoid year at each location showing all 48
genotypes. Lines are colored according to genotypes. Colors are consistent across different panels. The
red tick marks along the horizontal axis indicate time points at which biomass observations were used for
Bayesian hierarchical modeling.


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.


Figure 3: Fitted curves (posterior medians) for medoid year at each location showing all genotypes. Points
represent observations. Lines and points are colored according to genotypes. Colors are consistent across
panels. The time axis has been obtained by dropping the first 14 days after sowing and rescaling by
division by 10.


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.


Figure 4: Fitted curves (posterior medians) for medoid genotype in medoid year for each of 4 locations.
Observations at locations are distinguished by symbol: points, squares, triangles and crosses. Colored
bands represent 95% Bayesian (pointwise) prediction bands. Bands are colored according to locations.
The time axis has been obtained by dropping the first 14 days after sowing and rescaling by division by 10.


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.


Figure 5: Fitted curves (posterior medians) for the medoid genotype across all years at each of 4 locations.
Points represent observations. Lines and points are colored according to years. Colors are consistent
across panels. The time axis has been obtained by dropping the first 14 days after sowing and rescaling
by division by 10.


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.



_α_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;σ&#93;_ _&#91;p&#93;_



Figure 6: Posterior summaries for parameters _σ_ _α_ _&#91;p&#93;_ _&#91;,&#93;_ _&#91;σ&#93;_ _β_ _&#91;p&#93;_ &#91;,&#93; &#91;and&#93; _&#91;σ&#93;_ ( _&#91;p&#93;_ _α·β_ ) &#91;for&#93; &#91;each&#93; &#91;of&#93; &#91;the&#93; &#91;superscripts&#93; _&#91;p&#93;_ &#91; =&#93; _&#91; M&#93;_ &#91;,&#93; _&#91;mid&#93;_

and _r_ . Each panel gathers results for a different parameter of the log-logistic function, identified by labels
`Asymptote`, `Midpoint` and `Slope` . Points in the middle of the segments are posterior medians. The thick
and thin segments represent 67% and 95% credible intervals, respectively. No posterior densities are
plotted, as they are highly peaked for _σ_ _α_ _&#91;p&#93;_ &#91;and&#93; _&#91;σ&#93;_ _&#91;p&#93;_ _·_ &#91;parameters,&#93; &#91;and&#93; &#91;as&#93; &#91;such&#93; &#91;visually&#93; &#91;uninformative.&#93;



Figure 6: Posterior summaries for parameters _σ_ _α_ _&#91;p&#93;_




_&#91;p&#93;_ &#91;and&#93; _&#91;σ&#93;_ _&#91;p&#93;_

_β_ &#91;,&#93; (



_α_ _&#91;p&#93;_ &#91;and&#93; _&#91;σ&#93;_ _&#91;p&#93;_



( _&#91;p&#93;_ _α·β_ ) &#91;parameters,&#93; &#91;and&#93; &#91;as&#93; &#91;such&#93; &#91;visually&#93; &#91;uninformative.&#93;



30


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.



Figure 7: Posterior summaries for ratios _σ_ _&#91;p&#93;_



( _&#91;p&#93;_ _α·β_ ) _&#91;/σ&#93;_ _α_ _&#91;p&#93;_



Figure 7: Posterior summaries for ratios _σ_ ( _&#91;p&#93;_ _α·β_ ) _&#91;/σ&#93;_ _α_ _&#91;p&#93;_ &#91;for&#93; &#91;each&#93; &#91;of&#93; &#91;the&#93; &#91;superscripts&#93; _&#91;p&#93;_ &#91; =&#93; _&#91; M&#93;_ &#91;,&#93; _&#91;mid&#93;_ &#91;and&#93; _&#91;r&#93;_ &#91;.&#93; &#91;Labels&#93;

`Asymptote`, `Midpoint` and `Slope` refer to the parameters of the log-logistic function. Points in the middle
of the segments are posterior medians. The thick and thin segments represent 67% and 95% credible
intervals, respectively. The densities are the posterior densities.



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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.


Figure 8: Percentages of genotypes in individual trials with interactions ( _α · β_ ) _&#91;M&#93;_ _ij_ &#91;(for&#93; &#91;the&#93; &#91;asymptote&#93;

parameter _M_ _&#91;max&#93;_ ) whose 95% credible interval excludes zero. The higher this percentage, the more specific
are the environmental challenges imposed by the conditions.


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preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.


Figure 9: Percentage of interactions for individual genotypes ( _α · β_ ) _&#91;M&#93;_ _ij_ &#91;across&#93; &#91;all&#93; &#91;trials,&#93; &#91;whose&#93; &#91;95%&#93; &#91;credible&#93;

intervals exclude zero. This percentage can be read as a measure of stability. The lower the percentage,
the more stable is a genotype.


33


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Figure 10: Correlations between APSIM parameters, on the one hand, and the genotype main effects
_α_ _i_ _&#91;p&#93;_ &#91;,&#93; &#91;on&#93; &#91;the&#93; &#91;other,&#93; &#91;for&#93; &#91;superscripts&#93; _&#91;p&#93;_ &#91;=&#93; _&#91;M&#93;_ &#91;,&#93; _&#91;mid&#93;_ &#91;and&#93; _&#91;r&#93;_ &#91;.&#93; &#91;APSIM&#93; &#91;parameter&#93; &#91;labels&#93; &#91;are&#93; &#91;explained&#93; &#91;in&#93; &#91;Table&#93;

4. Each panel gathers results for a different parameter of the log-logistic function, identified by labels
`Asymptote`, `Midpoint` and `Slope` ; see Section 2.2.2 for the meaning of the parameters. Points correspond
to estimates, while segments are 95% asymptotic confidence intervals based on Fisher’s z-transformation.
The dashed red line has been added for reference to indicate zero correlation.


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## 1058 Appendix A Supplementary Figures


Figure 11: Trace plots for several model parameters. There are 4 Markov chains per parameter.


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Figure 12: The autocorrelation function for Markov chains of several model parameters. The figure is best
viewed sideways. There are 4 Markov chains per parameter. Each is identified by a number from 1 to 4.


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Figure 13: The residuals versus fitted values plots for an arbitrary selection of 4 genotypes in 4 trials.


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## 1059 Appendix B Supplementary Listings and Tables


Listing 1: Variable and parameter names in the **brms** model.


# Env : t r i a l i d e n t i f i e r


# geno : genotype i d e n t i f i e r


# biomass : scaled biomass


# dscaled : scaled time


# Asym: carrying capacity of the log − l o g i s t i c function


# tmid : midpoint parameter of the log − l o g i s t i c function


# slope : ( scaled ) slope parameter of the log − l o g i s t i c function


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Listing 2: Model formula as implemented in **brms** .


formula brms _&lt;_ − bf ( biomassn l f ( mubiomass˜ ˜ mubiomass,˜ Asym / (1 + ( dscaled / tmid)ˆ( − slope ) ) ),

n l f (Asym ˜ exp ( logAsym ) ),
n l f ( tmid ˜ exp ( logtmid ) ),
logAsymlogtmidl o g s l o p en l f ( slope˜˜ ˜ 11 1 exp ( l o g s l o p e+++(1(1(1 _||_ _|_ Env)Env)Env)) )+++, (1(1(1 _||_ _|_ geno )geno )geno )+++(1(1(1 _||_ _|_ geno : Env ),geno : Env ),geno : Env ),
nl = TRUE
)


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Listing 3: Priors for the **brms** model.


prior brms _&lt;_ − p r i o r s t r i n g (” normal (0, 2)”, c l a s s = ”sigma ”) +
p r i o r s t r i n g (” normal (2, 2)”, c l a s s = ”b”, nlpar = ”logAsym ”, coef = ” I n t e r c e p t ”) +
p r i o r s t r i n g (” normal (2, 2)”, c l a s s = ”b”, nlpar = ” logtmid ”, coef = ” I n t e r c e p t ”) +
p r i o r s t r i n g (” normal (2, 2)”, c l a s s = ”b”, nlpar = ” l o g s l o p e ”, coef = ” I n t e r c e p t ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”geno ”, nlpar = ”logAsym ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”geno ”, nlpar = ” logtmid ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”geno ”, nlpar = ” l o g s l o p e ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”Env”, nlpar = ”logAsym ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”Env”, nlpar = ” logtmid ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”Env”, nlpar = ” l o g s l o p e ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”geno : Env”, nlpar = ”logAsym ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”geno : Env”, nlpar = ” logtmid ”) +
p r i o r s t r i n g (” exponential (1)”, c l a s s = ”sd ”, group = ”geno : Env”, nlpar = ” l o g s l o p e ”)


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Table 5: Summary of the **brms** fit.

```
  Family: gaussian
  Links: mu = identity; sigma = identity

 Formula: biomass ~ mubiomass

      mubiomass ~ Asym/(1 + (dscaled/tmid)^(-slope))
      Asym ~ exp(logAsym)
      tmid ~ exp(logtmid)
      slope ~ exp(logslope)
      logAsym ~ 1 + (1 | Env) + (1 | geno) + (1 | geno:Env)
      logtmid ~ 1 + (1 | Env) + (1 | geno) + (1 | geno:Env)
      logslope ~ 1 + (1 | Env) + (1 | geno) + (1 | geno:Env)
   Data: data_small_subsampled (Number of observations: 61213)
  Draws: 4 chains, each with iter = 2500; warmup = 500; thin = 1;
      total post-warmup draws = 8000

 Group-Level Effects:
 ~Env (Number of levels: 124)

              Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
 sd(logAsym_Intercept) 0.42 0.03 0.37 0.48 1.01 414 986
 sd(logtmid_Intercept) 0.33 0.02 0.29 0.38 1.00 442 742
 sd(logslope_Intercept) 0.16 0.01 0.14 0.18 1.00 648 1216

 ~geno (Number of levels: 48)
              Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
 sd(logAsym_Intercept) 0.07 0.01 0.05 0.08 1.00 1390 2427
 sd(logtmid_Intercept) 0.05 0.01 0.04 0.06 1.00 1365 2506
 sd(logslope_Intercept) 0.04 0.00 0.03 0.05 1.00 2029 3698

 ~geno:Env (Number of levels: 5952)
              Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
 sd(logAsym_Intercept) 0.05 0.00 0.05 0.05 1.00 2860 5605
 sd(logtmid_Intercept) 0.01 0.00 0.01 0.01 1.00 1764 3395
 sd(logslope_Intercept) 0.00 0.00 0.00 0.00 1.00 2708 3828

 Population-Level Effects:
           Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS

 logAsym_Intercept 2.21 0.04 2.14 2.28 1.01 186 419
 logtmid_Intercept 2.09 0.03 2.02 2.15 1.03 119 182
 logslope_Intercept 1.29 0.01 1.26 1.32 1.01 303 653

 Family Specific Parameters:
     Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS

 sigma 0.18 0.00 0.17 0.18 1.00 5237 4733

 Draws were sampled using sample(hmc). For each parameter, Bulk_ESS
 and Tail_ESS are effective sample size measures, and Rhat is the potential
 scale reduction factor on split chains (at convergence, Rhat = 1).

```

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