A vineyard’s soil patterns track a mysterious grapevine disease

A disease that comes and goes

A grapevine can display striking, tiger-striped leaves one year and appear symptom-free the next. That unpredictability makes grapevine leaf stripe disease, or GLSD, difficult to understand: the absence of visible symptoms does not necessarily mean that fungi associated with the broader esca disease complex are absent from the wood.

A study in a commercial Cabernet Sauvignon vineyard in Bolgheri, Tuscany, suggests that the soil surrounding vines may be part of the puzzle. Researchers found that patches with more recurrent leaf symptoms tended to have sandier, less lime-rich soils, deeper roots and more available manganese than patches where symptoms recurred less often.

The findings come from a single, approximately 1.75-hectare vineyard and four soil profiles. They show associations, not proof that any soil property triggers or prevents disease. The work is described in a bioRxiv preprint that has not been certified by peer review.

Mapping vines and soil

The team surveyed approximately 10,000 standing vines at the start of the study, checking them each September from 2020 through 2024. Vines were classified as symptomatic if they had the characteristic striped leaves; some also showed wilting. The researchers mapped each vine and recorded the number of years in which symptoms appeared. Vines that died after recorded symptoms were also counted among diseased vines.

Individual symptomatic vines could sit next to apparently symptom-free ones. Even so, maps estimated from the observations showed areas with contrasting recurrence, especially when the researchers focused on vines that had displayed symptoms in at least three of the five years.

To investigate the ground beneath those patterns, the team used an electromagnetic induction sensor to map apparent soil electrical conductivity at three approximate depths. This measurement reflects several soil characteristics, including moisture and texture; it is not a direct test for disease. The researchers combined the conductivity and symptom maps to select four locations: two in areas with relatively low symptom recurrence and two in areas with higher recurrence, with medium and high conductivity represented in each pair.

At each location, they dug a trench beside a vine row and described the soil layers and roots. Samples from three positions along each trench were combined into one composite sample per layer for laboratory analysis. The researchers also estimated water-holding capacity and saturated hydraulic conductivity from soil properties rather than measuring those water characteristics directly in the field.

Contrasting ground beneath the vines

The two profiles from lower-recurrence areas had finer-textured, lime-rich soils and evidence of temporary waterlogging. Roots were concentrated mainly in the upper 60 centimetres. The two higher-recurrence profiles were generally sandier, contained less lime and more organic carbon and nitrogen, and had roots distributed down to the maximum observed profile depth of roughly 120–130 centimetres.

Estimated available water capacity in the upper metre was higher in the lower-recurrence profiles: 133 and 144 millimetres, compared with 110 and 108 millimetres in the higher-recurrence profiles. That comparison does not establish how much water the vines actually took up, particularly because roots extended deeper in the latter locations.

Available manganese also differed. Averaged across analysed soil layers, it was approximately 4.5–4.8 milligrams per kilogram in the lower-recurrence profiles and 14.7–14.8 milligrams per kilogram in the higher-recurrence profiles.

The conductivity maps helped the team choose contrasting soil locations, but conductivity itself was not significantly associated with symptom recurrence in their analysis. The authors therefore say it should not be used as a predictor of recurrence on the basis of these results.

A hypothesis, not a treatment

The manganese difference drew the researchers’ attention because, as the preprint reports, laboratory work has found that manganese can increase wood-degrading activity in Fomitiporia mediterranea, a fungus associated with the esca complex. The proposed connection is that greater manganese availability in soil might lead to more manganese in vine wood and, in turn, affect fungal decay.

Several links in that chain remain untested here. The researchers did not measure manganese in vine tissues or the extent of wood decay at the sampled sites. Nor did they manipulate manganese, water, fertility or rooting depth to see whether symptoms changed. Those soil characteristics varied together, making it impossible to isolate one as the cause.

The small number of profiles also limits the conclusions: two locations represented each recurrence category, and the samples within each soil layer were pooled. Results from one non-irrigated vineyard, one grape variety and one rootstock cannot be assumed to apply elsewhere. Finally, the study tracked visible leaf symptoms, not all infections; a vine without stripes could still harbour associated fungi.

The immediate result is therefore a set of leads rather than a recommendation to alter vineyard soils. Testing the manganese idea—and separating it from the effects of water, roots and other nutrients—will require targeted experiments and observations across more vineyards.