Endogenous Abscisic Acid in Relation to Bud Growth in Alternate Bearing `Valencia' Orange

Abstract

An investigation was conducted into the relation of ABA (cis-trans-abscisic acid) in the dormant buds of alternate bearing ;Valencia' orange (Citrus sinensis [L.] Osbeck) trees. ABA did not appear to be related to alternate bearing but t-ABA (2-transabscisic acid) did. There was 5- to 10-fold more t-ABA than ABA in the buds. There was more t-ABA in the buds of the "on" trees than in the buds of the "off" trees, and a drastic drop in t-ABA in both types of buds as spring growth approached. Bud dormancy and readiness for growth as related to t-ABA are discussed.