Morphological traits underlying differences in early vigor among four cotton genotypes

In comparison with other annual crops, cotton (Gossypium hirsutum L.) seedlings develop slowly after emergence. More rapid seedling development can provide advantages in limiting disease, insect, and weed impacts on cotton seedlings. Information on the mechanisms determining early vigor in cotton is limited. Therefore, three genotypes previously identified to differ in seedling vigor and one commercial cultivar were selected for detailed characterization of early growth in greenhouse and field conditions. Growing environment and genotype effects were significant for many of the measured traits. Environmental conditions prevailing in field and greenhouse conditions differentially affected seedling growth, including cotyledon biomass, root weight ratio (RWR), net assimilation rate (NAR), and specific leaf area (SLA). Genotypic differences were found in one or both environments for cotyledon area, area of the first leaf, total leaf area, and leaf, stem, root, and total biomass. Leaf weight ratio (LWR), stem weight ratio (SWR), RWR, LAR, and SLA differed among genotypes at most stages, but this was not the case for relative growth rate and NAR. The high‐vigor genotype generally had longer roots, larger cotyledons, greater cotyledon, stem, and total biomass, and greater SWR and RWR than the low‐vigor genotype. The low‐vigor genotype had the greatest LAR, SLA, and LWR among the four genotypes. Results obtained in this study suggest that factors such as the efficiency of photoassimilate conversion into biomass, energy density of the biomass, root carbon exudation, and/or photosynthetic rates differ between the low‐vigor and high‐vigor genotypes