Role of Cotyledon and Leaf Photosynthesis in Early Seedling Development of Cotton.

Stand establishment and early growth set the stage for the entire cotton (Gossypium hirsutum L.) growing season. Rapid early growth enhances the chances that cotton seedlings can outgrow damage by biotic stress factors, and may also improve their ability to tolerate abiotic stress conditions. However, our understanding of the genetic and physiological mechanisms governing early vigor in cotton is very limited. Previously, we characterized a large number of cotton genotypes for differences in early growth. Based on this screen, we have identified three genotypes with low, medium, and high vigor and have paired these genotypes with a commercial cultivar for further examination of the mechanisms contributing to the observed differences. The objective of this research was to identify contributions of individual leaf traits, including photosynthetic rate, SPAD value and leaf mass per area (LMA) to vigor differences among four cotton genotypes. Greenhouse and field experiments with plants grown in pots were conducted with measurements of individual leaf traits in 3-7 day intervals between ~15 and 60 days after planting. Significant variation was found for cotyledon and individual true leaf area, leaf biomass, LMA, leaf SPAD readings, and leaf photosynthetic rate among the four genotypes at most stages. The associations between individual leaf traits, leaf area, leaf biomass, LMA, leaf SPAD readings, and leaf photosynthetic rate of each genotype were investigated. While similar pattern with slight difference among genotypes were found within environment, differences between environments were observed.