Assessing agronomic and physiological traits during reproductive developmental stages for breeding upland drought-tolerant cotton

Increasing crop production in a changing climate is one of the challenges facing the agricultural research community. The goal of this study was to identify and evaluate specific determinant traits for improving water stress resiliency of cultivated upland cotton (Gossypium hirsutum L.). Two genotypes (PhytoGen 72 [PHY72] and Stoneville 474 [STV474]) representing different production regions of the US were evaluated for water stress resiliency under greenhouse conditions. More than 20 vegetative and reproductive traits were evaluated through six physiological reproductive stages, from plant emergence to open bolls and under two irrigation levels. Significant differences (p ≤ 0.05) were observed between irrigation levels for most traits within each genotype. PHY72 had rapid increases in plant height under regular water and limited water conditions (RW and LW). RW approximated daily evapotranspiration rates, while LW rate provided 50% less water by mass. However, by the fourth stage, peak blooming, the two genotypes were the same height, indicating that early and rapid vegetative plant growth from emergence to first reproductive stage was not a good indicator of improved growth and boll production under diverse irrigation levels. Some traits, such as leaf temperature, chlorophyll fluorescence yield, leaf and boll number, as well as leaf and reproductive fresh weight, showed clear differences between the two genotypes in one or both irrigation rates. Cotton breeders/geneticists currently cannot predict end-of-season productivity based on early-season evaluations under water stress conditions. Early season, controlled environment screening before field testing may reveal the genetic potential of breeding lines for water stress resiliency.