Flower Bud Abscission in Pistachio (Pistacia vera L.) as Related to Fruit Development and Other Factors1

Abstract In the pistachio, flower bud abscission is induced by seeded fruits during the summer, resulting in alternate bearing. The onset of abscission was not influenced by number of fruits, but rate and final percentage of abscission increased as fruit number increased. Twenty or more fruits per 1-year-old stem caused complete abscission. The course of abscission was correlated with rapid seed growth. Periodic defruiting indicated that induction of abscission preceded actual separation of buds by 28 days. A defoliation experiment and analysis of flower buds for N gave evidence that competition between fruits and buds for photosynthate and N is not the primary cause of abscission.