Role of gibberellic acid in cotton fibre development

Fibres of three cotton cultivars (Gossypium hirsutum H-4, H-8 and G. arboreum G. Cot-15) were analysed for growth in terms of fibre length and dry weight and endogenous gibberellic acid (GA(3)) content thrice during 1997-2000, at Rajkot. The development of cotton fibre was divided into four distinct growth phases but overlap between elongation and secondary thickening was considerable which suggests that both these phases are independent of each other. During fibre elongation, GA(3) content remained low and increased after a decrease in the rate of fibre elongation in all three genotypes. The long staple cultivar (H-4) showed highest endogenous GA(3) content followed by the middle one (H-8) and the short staple cultivar (G. Cot-15). In in vitro studies when GA(3), NAA or GA(3) + NAA was supplemented to the media, increase in fibre length of the short staple cultivar was maximum, followed by the middle one and the long staple cultivar. Both in vivo and in vitro findings suggest that GA(3) is one of the important factors that determine fibre length.