Hormonal and climatological aspects of dormancy in peach buds

Hormonal changes in leaf and flower buds of Prunus persica (L.) Batsch. (cv 'Springcrest'/seedling) occurring during the 1988/89 and 1989/90 rest periods were studied under three different climatic conditions, i.e. in north-eastern (Udine), central (Pisa) and southern (Palermo) Italy. 1H-indole-3-acetic acid (IAA), abscisic acid (ABA), and t-zeatin riboside (t-ZR) levels were determined by immunoassay using a McAb-ELISA kit. The end of dormancy was evaluated by forcing 1-year shoots collected from the three locations at intermittent periods during rest and monitoring percentage of budbreak. Chilling was estimated according to Fishman et al. (1987), while heat units accumulation was calculated according to Anderson et al. (1986). The IAA content dropped concurrently with the start of chilling accumulation and remained low throughout a large part of the rest period; an increase in auxin content was concurrent with tetrads formation, a phenomenon that did not appear to be related to the end of dormancy. ABA concentration in buds collected in Udine and Pisa was high during the early part of the rest period and then gradually declined, reaching the minimum concentration at budbreak. In Palermo, ABA content increased until the end of December, then gradually declined. No association was found between ABA level and release from dormancy, t-ZR level, low throughout the rest period, increased at bud swelling.