Genotypic and environmental effects on cottonseed oil, nitrogen, and gossypol contents in 18 years of regional high quality tests

Determination of environmental influence on seed traits is critical for genetic improvement of seed quality in upland cotton (Gossypium hirsutum L.). The objective of this study was to analyze the relative contribution of environment and genotype (G) for seed oil, nitrogen (N), and gossypol contents using historical data from the regional high quality (RHQ) tests conducted from 1996 through 2013. The 18-year tests of RHQ were divided into six 3-year cycles with an average of about 20 genotypes and 7–10 testing locations (loc) in each cycle. Variance components of oil, N, and gossypol contents were estimated in each cycle and expressed as percentages of the total variance. Highly significant G × loc effects were identified for all seed quality traits in each cycle. For oil content, variance estimates of G to the total variance ranged from 20 to 57 % in different cycles. For N content, loc was the main source of variance with variance estimates of loc to the total variance ranging from 44 to 73 % in different cycles. In most cycles, loc and G were the main source of variance for free-gossypol content. For most seed quality traits, there was not a clear trend of changes among testing cycles for the variance estimates of G to the total variance. Broad-sense heritability for oil content, N content, and free-gossypol ranged from 0.79 to 0.96, 0.65 to 0.86, and 0.28 to 0.93, respectively. Highly significant G × loc interactions indicate that multiple location trials for testing seed quality traits are necessary. However, heritability estimates for these seed traits indicate stability across environments as well as the potential for genetic improvement. Significant reduction in seed index was observed in half of the testing cycles with a range of 10.4–9.52 within cycles. Correlation between seed index and oil content was positive with r values ranging from 0.23 to 0.77 in different cycles.