Phenotypic variability in the US upland cotton core set for root traits and water use efficiency at the late reproductive stage

To incorporate root traits that improve water use efficiency (WUE) in cotton (Gossypium hirsutum L.) variety development, harnessing the genetic variability for root traits is essential. The objectives of this study were to characterize the US upland cotton core set for root traits and WUE and determine the traits associated with WUE. The core set includes 23 of the 381 accessions of the cotton diversity panel and represents 74% of the allelic diversity in US upland cotton. Plants were grown in polyvinyl chloride columns (125-cm height, 15-cm diameter) in a greenhouse in 2021-2022 and 2022-2023. Half of the columns contained a synthetic hardpan (1 cm thickness, 300 PSI penetration resistance) at a depth of 25 cm. Plants were harvested when >50% of the population opened bolls. Based on 16 root- and shoot-traits, water use, and WUE, Deltapine 14, Station Miller, and Southland M1 were the best performers, and Toole, Paymaster HS200, Western Stormproof, CD3HCABCUH-1-89, and PD 2164 were the poor performers irrespective of the presence or absence of hardpan stress to root growth. The WUE of the core set genotypes was positively correlated with very fine root (diameter <0.25 mm) length, surface area, and volume and total root weight (correlation coefficient >= 0.45). These traits serve as beneficial root traits for developing new varieties with enhanced WUE. The identified genotypes and traits will be valuable for developing the next generation of water-use-efficient cotton varieties with a broad genetic base through advanced breeding techniques involving genomic tools and genetic diversity.