Cotton (Gossypium hirsutum L.) is not only the dominant fiber crop grown worldwide, but it is also an important source of plant-based oil and protein. Previous research has documented a significant effect of cotton cultivar and nitrogen application individually on lint yield and seed composition, but very limited studies have evaluated the lint, seed, oil, and protein yield responses of cultivars with different seed mass and composition to a broad range of N application rates. The objective of this study was to evaluate the lint, seed, oil, and protein yield responses of cultivars with different seed mass and composition to N application rates (0-168 kg N ha(-1)) for field-grown cotton. A field experiment was conducted in Tifton, GA, USA during the 2019 and 2020 growing seasons that included six cultivars and six N application rates. Cultivar significantly affected seedcotton, lint, seed, and seed reserve yields in both growing seasons. Lint yield did not follow identical trends as seed yield mainly due to cultivar variation in lint percent. Similarly, protein and oil yield were influenced by cultivar variation in seed composition. Seedcotton, seed, protein, and oil yields continually increased with increases in N application from 0 to 168 kg N ha(-1), whereas for lint yield, all fertilized treatments produced comparable yields that were significantly higher (68%) than the 0 kg N ha(-1) treatment. We conclude that variability in the distribution of photosynthates to fiber and seed as well as seed oil and protein composition can significantly alter trends in fiber, seed, and seed component yields in response to cultivar or N application rates for field-grown cotton.

Drought negatively affects cotton growth and yield, whereas excessive irrigation can limit yield through excessive vegetative growth and poor fruit retention. Mepiquat chloride (MC) application limits plant height, improves fruit retention and hastens maturity in responsive cultivars. Thus, the objective of this study was to address the effects of cultivar, irrigation, and MC strategy on cotton growth, maturity, yield, and fiber quality. Therefore, a field study was carried out using three cultivars, three different irrigation treatments, and three different MC treatments during the 2020 and 2021 growing seasons. In both years there was an interaction between irrigation and MC management for plant height. In 2020, MC treatments hastened cutout by two to three weeks in irrigated plots but did not affect cutout date in dryland plots. 2020 and 2021 differed substantially in rainfall (347 mm and 735 mm, respectively from planting to harvest). 2020 was a dry year in which yield responded positively to irrigation and 2021 was a wet year in which yield responded negatively to irrigation. There was no effect of MC treatments or interaction between MC and any other effect on lint yield. Fiber length was reduced, whereas strength and micronaire were increased by drought stress in 2020. Increased fiber length, strength, uniformity, and micronaire were observed by MC application in both years. Therefore, we can conclude that aggressive MC management reduces vegetative growth, promotes earlier physiological maturity under wel-lwatered conditions, and affects fiber quality, but does not necessarily interact with irrigation management to affect lint yield.

Growth temperature and genotype can influence seedling vigor in cotton (Gossypium hirsutum L.), and identifying genotypes that can perform well under different temperature extremes may broaden the range of temperatures over which optimum growth could be obtained. To this end, a controlled environment study was conducted to evaluate the response of advanced breeding lines to growth temperature and to evaluate the utility of rapid, fluorescence-based measurements (the OJIP test) as indicators of plant growth response to day/night temperature regimes (20/15, 30/20, 35/25, and 40/30 degrees C). At two weeks after planting, growth analysis, chlorophyll fluorescence measurements, and pigment concentrations were obtained. Significant genotype, temperature, and interaction effects were observed for seedling growth parameters, and some of the key components of the thylakoid reactions. Specifically, the 35/25 degrees C treatment had the highest values for all growth parameters, with genotypic differences in growth primarily being observed at this regime. Energy trapping by photosystem II (PSII) (phi PO), intersystem electron transport (phi EO), and photosystem I end electron acceptor reduction (phi RO) were significantly affected by temperature, but each component differed in heat sensitivity. All growth parameters were significantly correlated with a number of OJIP parameters including quantum efficiencies and performance indices. However, the strongest positive associations were observed between quantum efficiencies and growth metrics, with phi EO exhibiting the strongest correlations with growth. Our observations indicate that rapid OJIP assessments can potentially be used as indicators of early season growth responses to temperature.

Excessive irrigation can reduce cotton yield, but studies assessing the relative contribution of component physiological processes to yield loss are limited. The objective of the current experiment was to quantify irrigation-induced yield loss attributable to Intercepted Photosynthetically Active Radiation (IPAR), Radiation Use Efficiency (RUE) and Harvest Index (HI). For three irrigation treatments (well-watered, over-irrigated, and dryland) during the 2018 and 2019 growing seasons, biweekly measurements of predawn leaf water potential (psi(PD)) and light interception were taken along with measurements of biomass, lint yield, fibre quality and harvest index. Irrigation effects on yield were only observed during the 2019 season, and the results showed that psi(PD) remained relatively high in both seasons and was rarely affected by irrigation treatment. A significant reduction in yield was observed for irrigated treatments, despite the dryland producing lower biomass. Any positive effects of IPAR and RUE on lint yield due to excess irrigation were offset by large declines in HI. We conclude that HI was the dominant contributor to yield loss due to excessive irrigation because reduced boll numbers and average boll mass were observed in plots with the greatest total above-ground biomass.