Relationship between Endogenous Auxin and Gibberellin Like Substances and Sex Expression in Papaya (Carica papaya L)

Abstract

               A study was made on the content of endogenous level of auxin and gibberellin like substances in different sex types of papaya plants as the possible mean in identifying sex expression of the plants and for further study on the modification of abnormality in sex expression. Papaya seedlings were grown from the seeds of crosses between hermaphroditic and male plants of the native cultivar, Fang. Sex expression of these seedlings was followed and shown to be in the ratios of male : female : hermaphroditic plants of 1 : 1 : 1. The endogenous level of auxin and gibberellin like substances in the third to the fifth leaves from the apex pf the plants aged 60,100 and 140 days after sowing were analysed using bioassay and high performance liquid chromatography (HPLC) techniques. The papaya plants studied were grown at the Central Laboratory and Greenhouse Complex, Kasetsart University, Kamphaengsaen Campus. The experiment was conducted from April 1986 to July, 1986.

                The results showed that the average content of the two natural substances between male and female plants as identified by bioassay method was clearly different from those obtained by using the HPLC method. At 60 days after sowing, while the plants are not flowering and their sexes con not be identified, the male, female and hermaphroditiv papaya plants differed in the average contents of auxin like substances. However, the average contents of gibberellin like substances were not significantly different among those three sexes. The average content of the auxin and gibberellin like substances in the male plants increased as the plants aged. However, in the female and hermaphroditic plants, the substances increased until the plants were 100 days old, thereafter the content decreased. This was in contrast to the content of gibberellin like substances which were increased as the plants aged. Among the three sexes, the male plants contained the highest level of the auxin and the gibberellin like substances, and the female plants had the least contents.