Quantitative Changes in Gibberellin-like Substances in Stem Apex of Lychee cv. HongHuay prior to Flowering

Abstract

The studies on quantitative changes in gibberellin-like substances in stem apex of lychee cv. Hong Huay prior to flowering were carried out, starting with the study on response of lettuce cultivars to GA₃ (Kyowa) by lettuce hypocotyl bioassay (LHB) method. It was found that the length of lettuce hypocotyls increased according to GA₃ (Kyowa) concentrations while Dresser was the cultivar which showed the highest response. Interaction was found between cutivars and GA₃ (Kyowa) concentrations, since different cultivar responded to GA₃ (Kyowa) concentrations differently. Standard curves of gibberellin-like substance quantification by the method of LHB. It revealed that the minimum detectable of GA₃ (Kyowa) was 1x10^-3 ppm, while linear regression responses of cv. Dresser was found between 1x109^-3-1 ppm. The effects of performing date of standard curve (72 days interval) were investigated while no effect was found.

An analysis of lychee shoot apex for determination of gibberellin-like substance activities in different Rf zones of the chromatogram showed that the gibberellin activities wer Rf 0.2-0.5.

Quantitative changes in gibberellin-like substances prior to flowering in stem apex of 4-5 years old lychee tree cv. HongHuay were studied from November 1995 to March 1996. The samples were taken from the orchard of Chiang Mai Land Development Station, Mae Rinn district, Chiang Mai, Thailand. It was found that activities of gibberellin-like substances in the 4^th week prior to flowering was high while it decrease in the 3^rd week and remained constant until the 2^nd week, then decreased again to minimum level in the 1^st week until flowering.