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以减轻大小年结果现象。然而，目前关于香橙（Citrus deliciosa）对外源施用赤霉酸的响应机制仍鲜有研究，且赤霉素的连续施用方案也尚未得到充分探讨。本研究以巴西南部地区的‘蒙泰格里纳’（Montenegrina）和‘雷尼亚’（Rainha）宽皮柑橘为试材，旨在评估连续施用赤霉酸（GA3）对低挂果期（小年）后春季开花量的抑制效果。试验设置为在小年树上以21天为间隔，连续施用1至4次浓度为40 mg·L⁻¹的赤霉酸，施用周期始于5月、止于7月。结果表明，与对照组相比，连续施用赤霉酸超过2次的蒙泰格里纳柑橘，其萌芽与开花量均显著降低；而雷尼亚柑橘仅需连续施用2次赤霉酸即可抑制萌芽，且相较于对照组，单次施用赤霉酸便足以降低其萌芽量。整体而言，施用赤霉酸均可降低两个供试品种的萌芽与开花量。果园树龄可能与其大小年结果程度相关，进而影响柑橘对赤霉素施用的敏感性强弱。