| Sumario: | Two cotton genotypes (Gossypium hirsutum L.), 'MCU-S' and 'PRS-72', were subjected to variations in full sunlight hours. In both varieties, three hours of daily sunlight delayed bud initiation and reduced growth and yield, but the six-hour treatment increased dry weight and seed cotton yield in 'PRS-72'. A similar increase in growth and yield in 'PRS-72' occurred when three or six hours of sunlight until bud formation was followed by normal sunlight, while in 'MCU-5' these treatments increased leaf weight and yield, respectively. A reduction to three hours of sunlight after flowering adversely affected the growth and yield of both varieties. The sunlight treatments differentially influenced the chlorophyll contents of these varieties. Since 'PRS-72' reacted comparatively more favorably to reduced sunlight hours during the vegetative phase, it may be well suited to rainy conditions in the cotton-growing areas of western and central India.
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