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Although genotypic and environmental contributions to yield and fiber quality have been studied extensively in cotton for decades, the near-constant release of commercially available genotypes necessitates re-evaluation for specific cotton production regions. Consequently, lint yield, lint percent, fiber length, fiber strength, fiber micronaire, and uniformity index were evaluated for seven commercially available cotton cultivars across 33 yield environments in on-farm trials throughout Georgia. The following were quantified: the percentage of variability in each response variable accounted for by genotype and environment, trait stability for each cultivar across all yield environments, and genotypic and environmental correlations between all parameters of interest. Environment was the dominant factor governing lint yield (96.1% environment, 1.2% genotype), fiber length (80.6% environment, 5.1% genotype), strength (47% environment, 27.7% genotype), micronaire (63.8% environment, 9.9% genotype), and uniformity (69.8% environment, 6.5% genotype). In contrast, lint percentage was impacted more by genotype (51.5%) than by environment (38.8%). 'PHY 565 WRF' was identified as the most stable cultivar across all yield environments for all agronomic and fiber quality traits examined. Environmental correlations showed that fiber length, strength, and uniformity were all positively correlated with yield. These findings suggest that any improvements in the yield environment brought about through improved production practices or favorable environmental conditions will be conducive to improving fiber quality in cotton. [ABSTRACT FROM AUTHOR]

Although cotton plant mapping has been valuable in understanding growth and development, variation in fruit distribution among plants is a significant mapping challenge. Choosing a sample that is large enough to generate useful information, but small enough to minimize time and resources, can make plant mapping more accessible for evaluating cotton crop growth characteristics throughout the cotton belt. The purpose of this research was to identify the effects of sample size and main-stem node grouping on sample variability. Plants were sampled in 10-m sections from six cotton cultivars at five locations in Georgia in 2009 and one location in 2010. The relative errors associated with sample sizes of one to 50 plants, as well as the statistical power associated with each sample size, were computed. On average, 37 plants per cultivar among five cultivars were required to reach a statistical power of 0.90, with the required number based on the magnitude of difference between cultivars in the fraction of plants having a boll at a given fruiting site. Grouping of main-stem nodes and the use of moving weighted averages decreased the error on a node-by-node basis. The use of these methods resulted in the loss of some node-by-node information that might be of value in particular cases, but the number of plants required to generate the same statistical power and standard deviation was decreased from a mean of 37 to a mean of 19 plants. These techniques should allow the use of smaller plant samples and make plant mapping more accessible. [ABSTRACT FROM AUTHOR]

Abstract: Previous investigations have demonstrated that photosystem II (PSII) thermostability acclimates to prior exposure to heat and drought, but contrasting results have been reported for cotton (Gossypium hirsutum). We hypothesized that PSII thermotolerance in G. hirsutum would acclimate to environmental conditions during the growing season and that there would be differences in PSII thermotolerance between commercially-available U.S. cultivars. To this end, three cotton cultivars were grown under dryland conditions in Tifton Georgia, and two under irrigated conditions in Marianna Arkansas. At Tifton, measurements included PSII thermotolerance (T 15, the temperature causing a 15% decline in maximum quantum yield), leaf temperatures, air temperatures, midday (1200 to 1400h) leaf water potentials (Ψ MD), leaf-air vapor pressure deficit (VPD), actual quantum yield (Φ PSII) and electron transport rate through PSII (ETR) on three sample dates. At Marianna, T 15 was measured on two sample dates. Optimal air and leaf temperatures were observed on all sample dates in Tifton, but PSII thermotolerance increased with water deficit conditions (Ψ MD =−3.1MPa), and ETR was either unaffected or increased under water-stress. Additionally, T 15 for PHY 499 was ∼5°C higher than for the other cultivars examined (DP 0912 and DP 1050). The Marianna site experienced more extreme high temperature conditions (20–30 days T max ≥35°C), and showed an increase in T 15 with higher average T max. When average T 15 values for each location and sample date were plotted versus average daily T max, strong, positive relationships (r 2 from .954 to .714) were observed between T max and T 15. For all locations T 15 was substantially higher than actual field temperature conditions. We conclude that PSII thermostability in G. hirsutum acclimates to pre-existing environmental conditions; PSII is extremely tolerant to high temperature and water-deficit stress; and differences in PSII thermotolerance exist between commercially-available cultivars. [Copyright &y& Elsevier]

Respiratory carbon evolution by leaves under abiotic stress is implicated as a major limitation to crop productivity; however, respiration rates of fully expanded leaves are positively associated with plant growth rates. Given the substantial sensitivity of plant growth to drought, it was hypothesized that predawn respiration rates (RPD) would be (1) more sensitive to drought than photosynthetic processes and (2) highly predictive of water-induced yield variability in Gossypium hirsutum. Two studies (at Tifton and Camilla Georgia) addressed these hypotheses. At Tifton, drought was imposed beginning at the onset of flowering (first flower) and continuing for three weeks (peak bloom) followed by a recovery period, and predawn water potential (ΨPD), RPD, net photosynthesis (AN) and maximum quantum yield of photosystem II (Fv/Fm) were measured throughout the study period. At Camilla, plants were exposed to five different irrigation regimes throughout the growing season, and average ΨPD and RPD were determined between first flower and peak bloom for all treatments. For both sites, fiber yield was assessed at crop maturity. The relationships between ΨPD, RPD and yield were assessed via non-linear regression. It was concluded for field-grown G. hirsutum that (1) RPD is exceptionally sensitive to progressive drought (more so than AN or Fv/Fm) and (2) average RPD from first flower to peak bloom is highly predictive of water-induced yield variability., (Copyright © 2015 Elsevier GmbH. All rights reserved.)