Key message

In this review, the main internal and environmental hypotheses regarding alternate bearing and abscission of inflorescence buds and also, the methods to mitigate this physiological phenomenon have been investigated.

Abstract

Alternate bearing is annually fluctuating heavy (‘on’) and light (‘off’) crops, which occurs in most fruit trees. There are multiple visible causes, decreased shoot growth and flower buds or imperfect flowers, but all occur in association with a heavy crop, suggesting a carbohydrate resource limitation to shoot growth, or flower initiation, induction or differentiation. Pistachios bear on 1-year-old shoots from axillary buds produced the previous year. The visible mechanism is bud abscission on current season’s growth during ‘on’ years and bud retention in low crop load (‘off’) years. Though bud abscission is visible, the underlying cause is unknown. This review classifies the multiple hypotheses as internal, genetic, carbohydrate resources and hormones or environmental, abiotic and biotic stresses. Our examination of potential hypotheses and recent research suggests alternate bearing in pistachio is a result of the carbohydrate resource limitation generated by the heavy ‘on’ year crop maturation. However, the specific signal producing bud abscission is unknown. Alternate bearing in pistachio can be mitigated by a vigorous rootstock, particularly if combined with proper pruning. We hypothesize the vigorous rootstock may produce a better carbohydrate resource status through a larger tree with more leaf surface area. The pruning does not address the bud abscission but alters the ratio of non-bearing to bearing shoots, resulting in a lower alternate bearing index. Furthermore, we conclude alternate bearing in pistachio, while a within shoot phenomenon, can be triggered by severe environmental events that damage a current crop.

中文翻译：

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开心果的替代轴承（Pistacia vera L.）：综述

关键信息

在这篇综述中，研究了关于花序芽的交替承载和脱落的主要内部和环境假说，以及减轻这种生理现象的方法。

抽象

交替出现的结果是每年在大多数果树中都发生重（上）和轻（上）作物的波动。有多种明显的原因，芽生长和花芽减少或花朵不完美，但都与重茬有关，这表明碳水化合物资源限制了芽的生长，或花的萌芽，诱导或分化。开心果具有上一年产生的腋芽的1岁新芽。可见的机制是芽脱落对“开”年期间当前季节的生长以及芽在低作物负荷（“关”）年中的滞留。尽管芽脱落是可见的，但根本原因尚不清楚。这篇综述将多种假设分类为内部，遗传，碳水化合物资源和激素或环境，非生物和生物胁迫。我们对潜在假说的检验和最近的研究表明，开心果中的交替轴承是由于大量的“年度”作物成熟而产生的碳水化合物资源有限的结果。但是，产生特定信号的芽脱落是未知的。旺盛的砧木可以减轻开心果中的交替结实，特别是与适当的修剪相结合时。我们假设有活力的砧木可能通过较大的树和更多的叶表面积而产生更好的碳水化合物资源状况。修剪不能解决芽脱落的问题，但会改变不承重芽与承重芽的比率，从而导致较低的交替承重指数。此外，我们得出的结论是，开心果中交替出现轴承，同时出现苗内现象，这可能是由破坏当前作物的严重环境事件触发的。