Fruiting of cotton IV. Nitrogen, abscisic acid, indole-3-acetic acid, and cutout

Abstract

Decreases in growth, flowering rate, and fruit (boll) retention of cotton ( Gossypium hirsutum L.) characterize cutout, a hiatus in fruiting. Nitrogen deficiency hastens cutout, and has been reported to cause an increase in the concentration of abscisic acid (ABA), a growth-inhibiting hormone. A field experiment was conducted with ‘Deltapine 61’ cotton to determine possible effects of N deficit on the concentrations of ABA and the growth-promoting hormone, indole-3-acetic acid (IAA), in cotton fruiting branches in relation to their growth, flowering rate, and boll retention. Three harvests were made during the fruiting cycle in 1987 to determine if the ABA concentration of fruiting branches increased or IAA concentration decreased as growth decreased during the season. Three harvests were made the next season (1988) to determine possible changes in concentrations of ABA and IAA in flower buds and flowers. Fruiting branches were always shorter on low-N than on high-N plants, and fruiting branches that developed late in the season were much shorter than those that developed early. The ABA concentrations in fruiting branches decreased after 9 July and ABA concentrations were always lower in fruiting branches of low-N than high-N plants. Therefore, the results do not support the hypothesis that ABA accumulates in N-deficient cotton fruiting branches and inhibits their growth. Decreasing concentrations of IAA, however, could have been a cause of decreased growth of fruiting branches. The IAA content of fruiting branches decreased during the fruiting cycle, and was lower in low-N than in high-N plants except in the last harvest. ABA increased and IAA decreased in 3-day-old bolls as boll retention decreased. The concentrations of ABA in flower buds and flowers did not increase during the season and were not affected by N deficiency. Likewise, the concentrations of IAA in flower buds and flowers were not affected by N. The concentration of IAA in flower buds decreased during the season, however. In general, the results support the hypothesis that the IAA of cotton fruiting branches is affected by N deficit, decreases during the fruiting cycle, and may be a factor in the decreases in growth, flowering, and boll retention commonly referred to as cutout.