Wild, feral and domesticated Brassica rapa respond differently to drought

Drought can slow a plant’s growth, disrupt photosynthesis and, in crops, threaten harvests. Plants may respond in different ways: some limit water loss, some maintain growth, and some recover photosynthetic activity after water returns. To explore how these responses vary with a plant’s history of domestication, researchers compared wild, feral and cultivated forms of Brassica rapa, a species that includes crops such as bok choy and turnip.

The study asks two related questions: do these groups differ in how they withstand drought and recover afterward, and are there particular accessions—distinct plant lines—that could be useful for future crop breeding?

A controlled dry spell, followed by rewatering

The researchers grew 25 accessions in a greenhouse: nine classified as wild, eight as feral and eight as domesticated. The cultivated group included turnips, oilseeds and leafy vegetables. Plants were assigned to blocks, with five blocks kept well watered and five subjected to drought. The drought group was watered at the start of the experiment and again three weeks later; controls were watered weekly.

Over four weeks, the team measured several features of plant performance. These included dry biomass, leaf carbon dioxide uptake under set measurement conditions, and water-use efficiency—calculated from carbon uptake and stomatal conductance, a measure related to how readily water vapor passes through leaf pores. They also measured the quantum yield of photosystem II, an indicator of light use in photosynthesis. At the end, they compared taproot biomass with water-use efficiency.

Biomass retention and recovery are related but different. Biomass retention compares the final biomass of drought-treated plants with that of well-watered plants. Recovery was assessed in part by measuring photosynthesis after droughted plants were watered again.

Wild accessions stood out on some measures

Drought reduced biomass overall: plants in the dry treatment averaged 78.6% of the biomass of plants in the watered treatment. Responses varied among accessions. Three wild accessions from Georgia, one domesticated accession from Finland and one feral accession from Guatemala had more biomass in the drought treatment than in the control. That finding applies to those accessions in this experiment; it does not mean drought generally increases plant growth.

Across the three categories, wild accessions had higher average biomass retention than domesticated accessions. Feral plants were not statistically distinguishable from either group in this comparison. The results therefore do not support treating feral plants as a uniform intermediate—or assuming they share the drought response of wild plants.

Photosynthesis showed another difference. After rewatering, wild accessions, on average, recovered maximum carbon-assimilation rates to levels not significantly different from their watered controls. Domesticated and feral groups still had lower rates than their respective controls. Some individual accessions, including the wild HRIGRU 8688 and the feral CR 2299, combined comparatively high photosynthetic rates with full recovery after rewatering.

The pattern was not simply that wild plants were less affected. During the dry period, wild plants showed a drought-related decline in photosynthesis. The researchers describe them as both more sensitive and more resilient: they experienced stress but recovered strongly after water returned. Quantum yield also remained lower in drought-treated wild plants after rewatering, even though their maximum carbon-assimilation rates had recovered. Different measurements can therefore tell different parts of the recovery story.

The team found a positive association between taproot dry biomass and instantaneous water-use efficiency. This is a correlation, not evidence that a larger taproot causes greater efficiency. The study did not find clear differences in biomass retention among the crop types tested, but each type was represented by only a few accessions.

What the results can—and cannot—tell us

The findings identify candidate genetic resources and traits for further research, particularly among wild B. rapa. They also caution against assuming feralization reverses domestication: feral populations have their own evolutionary histories and need not resemble wild populations in drought response.

The evidence comes from 25 accessions in one greenhouse experiment, with a specific watering schedule and measurements over four weeks. Greenhouse recovery of photosynthesis or biomass retention does not establish improved harvests under field conditions, across different drought patterns, or in other Brassica crops. The small numbers of accessions in the crop-type groups also limit conclusions about leafy, root and oilseed forms. Breeding with drought-response traits may involve trade-offs with yield or other desirable characteristics, which this experiment does not resolve.

This account is based on a bioRxiv preprint posted November 11, 2026. The preprint had not been certified by peer review at the time of posting. Its results are promising leads, not settled evidence that any accession will improve drought resilience in farmers’ fields.