ABSCISSION OF FLOWER PEDUNCLES IN ROSE (ROSA X HYBRIDA) PLANTS

Abscission of flower buds was not observed when plants or harvested fl owers of rose cultivars 'Nubia' and 'Celica', grown for cut flowers we re kept for 3 weeks at 22-degrees-C in the dark. However, all young bu ds of the miniature rose cultivar 'Orange Meillandina' abscised after 6 days of darkness. Removal of buds at early stages of development res ulted in abscission of peduncles left intact on the plant in all culti vars examined. Girdling of the stem combined with defoliation postpone d the abscission of decapitated peduncles of 'Nubia' in situ. The time to abscission of decapitated peduncles in explants was similar to tha t on the plants in situ. Abscission of peduncles, although delayed, wa s also present in non-decapitated explants of 'Nubia', 'Celica', and ' Yellow Meillandina' with young buds. In contrast, in the whole plant, darkness did not induce abscission in non-decapitated explants of 'Ora nge Meillandina'. Abscission of decapitated peduncles of 'Nubia' on th e plant was postponed by application of either indoleacetic acid (IAA) or gibberellin (GA3), while only IAA applied to the distal end of the peduncle inhibited peduncle abscission in explants. The abscission of decapitated peduncles in explants was promoted by abscisic acid (ABA) and in non-decapitated explants by application of 2,3,5-triiodobenzoi c acid (TIBA) as a lanolin ring beneath the bud. The possible involvem ent of three components originated in flower buds, leaves or roots in the phenomenon of flower bud abscission in rose plants is discussed.