Evaluation of modern and obsolete cultivars under contrasting environmental conditions for explaining yield variability in cotton

Year-to-year variability in yield of modern cotton cultivars has become a major concern in the cotton industry. High yield variability may be due to modern cultivars being more sensitive to environmental stress conditions compared to obsolete cultivars, but evidence is lacking. Therefore, field and growth chamber studies were conducted in Arkansas from 2000-2004 to determine the growth and development, physiological response, and yield of modern versus obsolete cultivars as influenced by water-deficit and high daytime temperature stresses.; Results from this four year study indicated that under optimum environmental conditions (2001-2003) modern cotton cultivars produce higher yields as a result of higher seed numbers per hectare and a greater weight of fiber per seed. However, under a moderate to severe drought stress (i.e., in 2000) the obsolete cultivars produced the highest lint yields due to more fiber per seed and relatively similar seed number compared to modern cultivars. Yield variability was measured between site years and indicated 31.2% variability by modern cultivars and 26.2% variability between years by obsolete cultivars averaged over water treatments.; Modern and obsolete cultivars had similar plant heights, main-stem nodes, vegetative-to-reproductive ratios, and total dry weights. Similarities in total dry weight between modern and obsolete cultivars was the result of greater leaf dry weights by the obsolete cultivars, but increased fruit dry weight by the modern cultivars. Modern cultivars had a greater fruit number, increased SLW, and higher values for CGR and NAR. Petiole nutrient analysis indicated differences between modern and obsolete cultivars, but results varied depending on the specific nutrient, sampling time, and water status. Growth analysis and NAWF counts indicated that modern cultivars matured earlier than obsolete cultivars due to more rapid boll development and increased crop growth rates.; Modern cultivars had better physiological responses under ideal temperature environments, whereas obsolete cultivars tended to be less sensitive to extreme temperatures and water-deficit stress resulting in better photosynthesis, chlorophyll fluorescence, membrane integrity, greater protein levels, and a more efficient antioxidant defense system. Improved physiological responses by obsolete cultivars under environmental stress conditions is likely the reason for increased yield variability in modern cultivars.