Photosynthesis and Leaf Characteristics of Cotton Genotypes Differing in Early Vigor

Stand establishment and early growth set the stage for the entire cotton 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 screened 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.  Measurements of leaf areas and photosynthesis conducted between ~15 and 60 days after planting, revealed that cotyledons of the high- and medium-vigor lines were greater than those of the low-vigor genotype.  In addition, the cotyledon dry weight of the most vigorous line tended to be greater than that of the other lines during the first 30 days after planting.  The greater cotyledon dry weight was not only caused by greater leaf area, but was also the result of increased specific leaf weight.  Future in-depth examination of the first and second true leaves, as well as the investigation of the carbohydrate dynamics, will be conducted to elucidate the mechanisms underlying differences in seedling vigor.