No 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.

No abstract

Lint yields and their underlying yield components can be substantially influenced by genotype and environment. Thus, the objectives of the current study were to quantify genotypic and environmental contributions to lint yield, yield components, and fiber quality in multi‐site variety trials conducted in Arkansas over a 19‐year period, to identify the traits most strongly associated with lint yield, and to quantify long‐term trends in the aforementioned traits. Annual assessments included lint yield, seeds per hectare (SPH), intra‐boll yield components, and fiber quality parameters. Production environment accounted for a higher percentage of all yield variability in 15 out of 19 years. However, four years were identified in which genotypic contributions were greater than environmental contributions. Genotype was a dominant driver of variability in lint percent, lint index, seed score, seed index, fibers per seed, fiber density, fiber length, strength, and uniformity. Production environment was the dominant driver of variability in SPH, and micronaire. Correlations between yield components and yield varied substantially from year to year, even when genotype was the primary yield driver. A regression function that utilized lint index and SPH was a stronger and more consistent indicator of genotypic variation in lint yield than any single yield component. Finally, long‐term trends show that lint percent has increased significantly over the past 19 years, whereas seed index has declined 19.6% for cotton varieties with the highest lint yields.

Nitrogen (N) deficiency limits net carbon assimilation rates (AN), but the relative N sensitivities of photosynthetic component processes and carbon loss mechanisms remain relatively unexplored for field-grown cotton. Therefore, the objective of the current study was to define the relative sensitivity of individual physiological processes driving N deficiency-induced declines in AN for field-grown cotton. Among the potential diffusional limitations evaluated, mesophyll conductance was the only parameter substantially reduced by N deficiency, but this did not affect CO2 availability in the chloroplast. A number of metabolic processes were negatively impacted by N deficiency and these effects were more pronounced at lower leaf positions in the cotton canopy. RuBP regeneration and carboxylation, AN, and gross photosynthesis were the most sensitive metabolic processes to N deficiency, whereas photosynthetic electron transport processes, electron flux to photorespiration, and dark respiration exhibited intermediate sensitivity to N deficiency. Among thylakoid specific processes, the quantum yield of PSI end electron acceptor reduction was the most sensitive process to N deficiency. It was concluded that AN is primarily limited by Rubisco carboxylation and RuBP regeneration under N deficiency in field grown cotton and the differential N-sensitivities of the photosynthetic process and carbon loss mechanisms contributed significantly to photosynthetic declines.