Successive applications of gibberellic acid in alternate bearing mandarins

Aplicações sucessivas de ácido giberélico em tangerineiras em alternância de produção

Abstract

Gibberellins can promote the inhibition of floral induction in citrus in order to reduce alternate bearing. However, not much is known about the responsiveness of Citrus deliciosa to exogenous applications of gibberellic acid. Furthermore, the successive application of gibberellins is barely studied. The main objective of this work was to evaluate the effect of successive applications of gibberellic acid (GA₃) on the reduction of spring flowering subsequent to low fruit load periods (off-year) in ‘Montenegrina’ and ‘Rainha’ mandarin trees, in southern Brazil. The treatments consisted of one to four successive applications of GA3 (40 mg L^-1) with 21-day interval in off-year trees. Applications began in May and ended in July. There was a significant reduction in sprouting and flowering of ‘Montenegrina’ mandarin with more than two GA₃ successive applications compared to the control. To ‘Rainha’ mandarin, only two GA₃ applications reduced the sprouting and solely one GA3 application was enough to reduce sprouting in relation to the control. GA₃ use reduced sprouting and flowering of Montenegrina and Rainha cultivars. The orchard age may be related to its level of alternate bearing and, therefore, to the greater or lesser sensitivity of gibberellin applications.

Index terms
plant growth regulators; citrus; Citrus deliciosa Tenore; flowering