SEASONAL FLUCTUATION OF ABSCISIC ACID AND CYTOKININS IN TWO PEACH PRUNUS PERSICA (L.) BATSCH CULTIVARS

Excised buds of shoots of 'Siberian C' and 'Harrow Blood' peach trees were collected bimonthly starting in mid-July 1981 until April 1982 for abscisic acid (ABA) and cytokinins analysis. Leaves of the same shoots from both cultivars were harvested for ABA analysis during July to October 1, 1981.;Onset of dormancy in both cultivars was associated with high levels of ABA and low levels of zeatin and zeatin riboside. 'Siberian C' buds showed earlier and higher levels of ABA throughout the study period, earlier cessation of terminal bud extension growth and early defoliation than 'Harrow Blood'. Innate bud dormancy in both cultivars was terminated by the end of December.;Bud dormancy during winter and early spring in both cultivars was associated with low levels of ABA, zeatin and zeatin riboside. Bud burst in 'Harrow Blood' was earlier than in 'Siberian C' and in both cultivars high levels of zeatin and zeatin riboside were observed following this event.;The methods of Takeda and Crane J. Amer. Soc. Hort. Sci. 4: 573,1980 and During and Bachmann Physiol. Plant. 34: 201, 1975 were used for ABA analysis while the methods of Kannangara et al. Physiol. Plant. 44: 295,1978, Shinday and Smith Plant Physiol. 55: 550, 1975, Taylor et al. Physiol. Plant. 30: 119, 1974, and Thomas et al. Plant Physiol. 56: 410, 1975 were used for cytokinin analysis. The presence of both plant hormones was confirmed by thin layer chromatography (TLC), wheat coleoptile (ABA) and cucumber (chtokinins) bioassay and high performance liquid chromatography (HPLC).