Wheat breeding highlights drought tolerance while ignores the advantages of drought avoidance: A meta-analysis


Li, P., Ma, B., Palta, J.A., Ding, T., Cheng, Z., Lv, G., Xiong, Y. (2021). Wheat breeding highlights drought tolerance while ignores the advantages of drought avoidance: A meta-analysis. European Journal of Agronomy, [online] 122 http://dx.doi.org/10.1016/j.eja.2020.126196

Plain language summary

Drought is the most critical factor limiting crop production worldwide. Plant survival and productivity in water-limited environments depend on a range of adaptive mechanisms, including drought escape, drought avoidance and drought tolerance. Drought escape is characterized with a rapid phenological development, which allows the plants to complete their reproduction before the onset of drought. Drought avoidance involves mechanisms, such as reduction in leaf area and stomatal conductance, to reduce transpiration rate. Another strategy of drought avoidance is through a well-developed and deep root system, which is related to the capacity to enhance water uptake and plays a critical role in maintaining water supply. In contrast, Drought tolerance mainly relies on osmotic adjustments to maintain turgor and cell volume, which allows the plants to ensure growth under water stress. Breeding for crop drought resistance has been a key area of research in the past several decades. However, available information on crop drought resistance is limited, particularly to answer the following questions: (1) How does drought avoidance and tolerance evolved in crop during domestication; and (2) How to bridge the gap between theoretical research discoveries and crop breeding practices.

In this study, we used a meta-analysis approach to systematically assess the mainstream features of drought avoidance and tolerance traits involved in dryland wheat breeding programs. Specifically, we aimed to evaluate the evolutionary trend of drought avoidance and tolerance during the process of wheat domestication. We hypothesized that yield oriented wheat breeding process would have mostly focused on improving drought tolerance, while weakening drought avoidance.

Our results demonstrated that wheat breeding process has always highlighted drought tolerance, but has continued obscuring the advantages of drought avoidance. We documented that drought avoidance and tolerance have made different contributions to grain yields. Under severe water stress, wheat genotypes that preferentially displayed drought avoidance characteristics resulted in less reduction in grain yield and aboveground biomass, while genotypes that exhibited stronger drought tolerance produced higher grain yield and aboveground biomass under mild and moderate water stress. Therefore, incorporating drought avoidance into drought tolerant genotypes for future cultivar improvement is an important strategy to deal with climate change. The results from this study provide a firm basis for important and informed decisions on the impact of drought resistance in modern plant breeding.


Crop tolerance and avoidance are critical adaptation mechanisms to cope with drought stress but they contribute differently to grain yield formation. Little is known about the different roles of these two mechanisms in long-term crop breeding. A meta-analysis was conducted to determine the different effects of drought tolerance and avoidance mechanisms on the drought adaptation of wheat crops. The meta-analysis summarized the results of 283 published papers in international journals, and illustrated that primitive wheat genotypes, including wild, cultivated diploids, tetraploids and old hexaploids, preferentially showed a drought avoidance strategy, as evidenced by large root biomass, small leaf area, and reduced stomatal conductance under water deficits. Modern hexaploid genotypes showed stronger drought tolerance advantages, such as high leaf water potential and osmotic adjustment, with a small root system. The meta-analysis indicated that the breeding process of dryland wheat has been continuously enhancing drought tolerance while weakening drought avoidance. Under severe water deficits, old hexaploid wheat genotypes with drought avoidance characteristics showed lower reduction of aboveground biomass and yield than modern genotypes with stronger drought tolerance features, while under mild and moderate water deficits genotypes with stronger drought tolerance features had higher yields and aboveground biomass. The meta-analysis provide information for making decisions on the direction of modern crop breeding and the implementing of managing practices to cope with drought stress, which frequency and severity is increasing with the advent of climate change.

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