Chemical control of flower development in sweet orange (Citrus sinensis)

Abstract

Several growth retardants (2-chloroethyltrimethylammonium chloride, 2,3,5- tri-iodobenzoic acid, maleic hydrazide, morphactin IT3456) and also ethylene chlorhydrin were screened for possible effects on the flowering of sweet orange. No stimulation of flowering was found. In two experiments in the field, applied gibberellic acid (GA) decreased flowering though it increased the proportion of the more leafy inflorescences (and usually more fertile inflorescences); in some instances an increase in percentage fruit set also occurred, although the total number of fruits formed was less than in the control. The increase in percentage fruit set by some GA treatments appeared to be the result of fewer inflorescences, and thereby reduced competition, rather than an enhancement of the fertility of inflorescences. These effects of applied GA were greatest when applications were in late June or early July. It is suggested that floral initiation was occurring at that time. Increasing the concentration of GA above 25 p.p.m. did not cause any further reduction in flowering, but increased the proportion of leafy inflorescences. The possibility of using GA to prevent alternate bearing is discussed.