Better root length distribution in the deep soil profile enhances upland cotton performance

Intense selection for lint yield and fiber quality traits can impose an unintended limitation on the attainable yield of modern cotton cultivars, as the root systems fail to support boll growth. Despite the importance, little progress has been made in enhancing cotton root systems. We evaluated a subset of the U.S. cotton diversity panel under field conditions in 2022 and 2023 to identify the root architectural traits that enhance effective water use and aboveground performance. We found that increased water use efficiency (WUE, shoot biomass/soil water depletion) of the cotton genotypes was associated with enhanced shoot biomass (correlation coefficient, r, 0.80 in 2022 and 0.96 in 2023). Potential root phenotypes that enhanced resource capture and shoot biomass production were better root length distribution in deep soil profile (∼40–60 cm) and fine root (0.25–0.5 mm diameter) production. Shoot biomass was correlated with root length in the deep profile (r, 0.69 in 2022 and 0.45 in 2023) but not in the shallower profile (<40 cm). Root length in the deep profile was also correlated with WUE in the dryer year 2022 (r, 0.45). The cotton root system was dominated by fine roots (46–66 % in 2022 and 53–62 % in 2023). Genotypes Station Miller, Paymaster HS26, and PD 2164 possessed beneficial root architecture which was linked to their high shoot biomass, leaf area index, WUE, and seed cotton yield. These genotypes can be used as germplasm sources for improved root traits and to study their genetic regulation. • Increased shoot biomass increases the water use efficiency (WUE) of cotton. • Fine root production and deep rooting improve shoot biomass and WUE. • Station Miller, Paymaster HS26, and PD 2164 possessed beneficial root architecture. • These genotypes offer useful genetic material for improving WUE and root traits.