Analysis of root characteristics and drought resistance of different cotton varieties

Short-root cotton varieties showed a greater increase in total root length under drought, while long-root varieties increased root biomass. Certain short-root varieties (e.g., HN79) demonstrated relatively smaller reduction in yield under drought stress. GWAS identified GhAIL6 on chromosome At02 as a key gene promoting cotton root growth. The root system is an important organ for cotton to absorb water and nutrients. Different cotton varieties respond differently to drought stress. Therefore, this study firstly conducted an indoor experiment using 384 cotton varieties as materials, to screen long and short root varieties. Subsequently, a field experiment was performed to analyze the differences in drought responses between these two types of varieties. And then through genome-wide association analysis (GWAS), screened for candidate genes. The research results showed that, based on the total root length (TRL) as the main indicator in the indoor experiment, five long-root type varieties PD2164, B557, CCRI No.30, Super Jijiao Dezi Mian and Dunn HS120, and five short-root type varieties Bole 34, Henan No.79, CCRI No.50, V83-013 and Ari3696 were selected. The results of the drought stress experiment showed that under drought conditions, the average TRL increase of long-root type varieties (5.49%) was smaller than that of short-root type varieties (15.45%, P <0.05); the yields of long-root type varieties and short-root type varieties decreased by 19-35% and 10-37% respectively. It is notable that under drought conditions, the TRL increase of short-root type variety HN79 was the highest, at 69%, and the yield decrease was the lowest, at 10%, demonstrating higher drought resistance. We also identified SNPs related to the primary root traits in the At02 region 101.2-101.6 Mb through GWAS, and determined that GhAIL6 is a root development-related gene. This study identified ten cotton varieties exhibiting extreme long-root and short-root phenotypes. Further analysis showed that some short-root varieties exhibited greater increases in total root length and smaller reductions in yield under drought stress, indicating stronger drought resistance. Additionally, the study elucidated the pivotal role of GhAIL6 in promoting root growth during the cotton seedling stage.