Growth, photosynthesis, and carbohydrate dynamics of cotton during early development

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Stand establishment and early growth is critical for successful cotton (Gossypium hirsutum L.) production. 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, information about the physiological mechanisms governing early vigor in cotton is limited. Therefore, three cotton genotypes differing in seedling vigor and one commercial cultivar were selected for detailed characterization of early growth in greenhouse (GH) and in field conditions. Phenotypes measured included total biomass, total leaf area, leaf area ratio, specific leaf area, net assimilation rate, absolute growth rate, relative growth rate, individual leaf biomass, leaf mass per area, SPAD readings, and photosynthetic rates. Additionally, temporal dynamics of fructose, glucose, sucrose and starch concentrations in leaf, cotyledon, stem, and root tissues were characterized in detail in the four genotypes. Significant genotypic differences were observed for most of the parameters. Genotypic differences in leaf area ratio, specific leaf area, leaf weight ratio, stem weight ratio, and root weight ration indicate that carbon allocation was strongly influenced by genotype. Genotypes also differed in cotyledon size and areas of individual true leaves, leaf biomass, leaf mass per area, SPAD readings, and photosynthetic rates at most measurement dates. Differences in carbohydrate concentrations were observed among tissue types, genotypes, and between greenhouse and field experiments. Carbon allocation to different tissues, leaf area, and photosynthetic rates appear to be important drivers underlying early vigor in cotton, and the extent to which the differences in carbohydrate concentrations and dynamics are responsible for, or a consequence of, differences in early vigor remains to be elucidated.