THE EFFECT OF GIBBERELLINS AND GROWTH-RETARDANTS ON INVITRO FLOWERING OF THE VEGETATIVE APEX OF JAPANESE PEAR

Effects of gibberellins GA3 and GA4 and of growth retardants succinic acid-2,2-dimethylhydrazide (B-9), (2-chlorethyl)trimethylammonium chloride (CCC) and (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (S-3307) on flowering of Japanese pear cultivars 'Kosui' and 'Chojuro' were investigated. Explants were prepared from the shoot apex or the axillary bud. The presence of GA4 but not GA3 in the culture medium tended to decrease flowering of 'Chojuro' explants, although inhibition was less clear in 'Kosui' explants which showed low flowering percentages. S-3307 effectively promoted flowering, particularly for 'Kosui' explants. The promotive effect of CCC was slight or none, and B-9 reduced flowering. GA4 (but not GA3) or the growth retardants had a tendency to increase or decrease shoot and internode length of the explants; these morphological changes were not always associated with flowering behavior. The growth regulators had little or no effect on node number of the explants, which was closely related to flowering. Successive subculture of the vegetative apex in the adult form resulted in a rapid loss of flowering ability with an increase in shoot or internode length in the resulting explants, shifting to juvenile characteristics. © 1990.