Successive applications of gibberellic acid in alternate bearing mandarins

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.

摘要：赤霉素（Gibberellins）可通过抑制柑橘成花诱导，从而减轻植株的大小年结果现象。然而，目前学界对于柑橘（Citrus deliciosa）对外源施加赤霉素的响应机制仍知之甚少，且针对赤霉素连续施用的相关研究亦较为匮乏。本研究的核心目的为评估连续施加赤霉素（GA3，Gibberellic acid）对巴西南部‘Montenegrina’与‘Rainha’两个宽皮柑橘品种在低挂果量年份（小年）后春季开花量的调控效果。试验设置了1至4次连续施加赤霉素（浓度为40 mg·L⁻¹）的处理组，施加间隔为21天，施药周期始于5月、终于7月。结果显示，与对照组相比，‘Montenegrina’宽皮柑橘在连续施加2次以上赤霉素后，其芽萌发与开花量均显著降低；而‘Rainha’宽皮柑橘仅需2次赤霉素施加即可抑制芽萌发，且单次施加即可达到相较于对照组降低萌发率的效果。赤霉素施用可有效降低‘Montenegrina’与‘Rainha’两个品种的芽萌发与开花量。此外，果园树龄可能与植株大小年结果程度相关，进而影响其对赤霉素施用的敏感性高低。