Physiological Contributors to Early Season Whole‐Crop Vigor in Cotton

ABSTRACT Cultivar and early growth conditions are known to influence seedling vigor in cotton (Gossypium hirsutum L. and Gossypium barbadense L.). What has not been explored fully is the relative importance of physiological contributors to early season, whole‐crop growth under field conditions. It was hypothesized that variability in early season crop growth will be associated, to varying degrees, with leaf area development and whole‐canopy net assimilation rate (NAR). To test this hypothesis, three cultivars with anticipated differences in seedling vigor were planted in 2017 and 2018 on three different dates each year to generate differences in early season crop growth. For crop growth rate (CGR) and leaf area index (LAI) there was a significant interaction between cultivar and planting date in both years. In 2017, only planting date significantly affected NAR, but in 2018, planting date and cultivar main effects were observed for NAR. When considered across both years, variability in early crop growth, whether driven by cultivar or planting date, was strongly and positively associated with LAI, but only weakly associated with NAR. High early season LAI and CGR were also positively correlated with leaf area per plant but not leaf area ratio, specific leaf area, or leaf fraction. Thus, vigorous whole‐crop growth in the early season is more dependent on leaf area development than specific leaf activity.