Background Root spatial distribution, as an important phenotype trait of root function, is closely related to drought tolerance. Drought hinders cotton development during the growing stage. However, the effects of drought at the square stage on the spatial distribution characteristics of cotton roots at the flower-boll and boll opening stages are still unclear.
Methods To address this gap, 30 different cotton cultivars were cultivated in the field. The control treatment received routine irrigation (1175 m3·hm-2) and drought stress treatment received reduced irrigation (822.5 m3·hm-2). Multiple parameters, including root traits, above-ground traits, and yield, were assessed.
Results At flower-boll stage, drought stress during the square stage significantly reduced SPAD and Fv/Fm in cotton. Cluster analysis categorized all cultivars into drought-tolerant, relatively drought-tolerant, intermediate-sensitive, relatively drought-sensitive, and drought-sensitive cultivars. Under drought stress, drought-tolerant cultivars exhibited a bigger decrease in average lateral root angles, a less pronounced increase in root/shoot ratio and 24.25% higher yield than drought-sensitive cultivars. Additionally, at 50-60 cm soil layer, root length density in drought-tolerant cultivars increased by 141.78%, compared to drought-sensitive cultivars under drought stress, and two cultivars were symmetrically distributed in the 0-30 cm soil layer. Interestingly, due to substantial rainfall, there were no significant differences in root spatial distribution at boll opening stage.
Conclusion In summary, drought at the square stage can improve drought tolerance and reduce yield losses by reducing the lateral root angles, optimizing root/shoot ratio and increasing root length density in deeper soil layer during the flower-boll stage.
