Growth and flowering of cotton (Gossypium hirsutum L.) as affected by daylength and temperature

SummaryOver 14 h of daylight and high day temperature singly or in combination delayed flowering of the upland cotton J 34, whereas the photosensitive variety MCU 5 did not flower under long days alone or long days plus high temperature. These treatments promoted vegetative growth and made the plants tall and bushy. Though the treatments were discontinued 75 days after germination the subsequent reproductive growth was adversely affected with significant reduction in boll weight.The upland genotypes when grown at latitudes 29° N, 21° N and 11° N flowered progressively earlier and at lower nodes at more southerly latitudes because of reduction in daylength and temperatures. It is concluded that the upland cottons of northern India differ from classical types because daylength together with temperature appeared to determine flowering.