Abstract
The heavy blooming of apple trees results in the inefficient usage of energy and nutritional material, and additional expenditure on fruitlet thinning is required to maintain fruit quality. A possible solution for controlling the fruit load on trees is the development of new cultivars that self-eliminate excess fruitlets, thus controlling yield. The aim of our study was to identify biological differences in apple cultivars in terms of blooming intensity and fruitlet load self-regulation. In total, 19 apple cultivars were studied in the years 2015–2017. The dynamics of fruitlet self-elimination, seed development in fruitlets and fruits, photosynthetic parameters, carbohydrates, and plant hormones were evaluated. We established that apple cultivars self-eliminating a small number of fruitlets need a lower number of well-developed seeds in fruit, and their number of leaves and area per fruit on a bearing branch are larger, compared to cultivars, self-eliminating large numbers of fruitlets. A higher carbohydrate amount in the leaves may be related to smaller fruitlet self-elimination. The amount of auxin and a high indole-3-acetic acid/zeatin ratio between leaves of cultivar groups with heavy blooming were higher than in cultivars with moderate blooming. A lower amount of abscisic acid was found in heavy-blooming cultivars during drought stress. All these parameters may be used as markers for the selection of different apple genotypes that self-eliminate fruitlets.
Highlights
The apple tree load of blossoms and fruitlet self-elimination depend on the cultivar
The influence of indole-3-acetic acid (IAA), abscisic acid (ABA), GA3, and Z was evaluated on yield self-regulation in apple, and we found that IAA, ABA, and the ratio between IAA and Z had the largest impact (Table 4)
The apple cultivars differ in terms of the total number of seeds and the minimum number of seeds required for fruit development
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Apple (Malus × domestica Borkh) is one the most important fruit trees in the temperate climate zone. Stable bearing and the production of high-quality fruits are crucial for growers. 5–10% of flowers grow to fruits; heavy blooming results in inefficient usage of energy and nutritional material [1]. Highquality harvest and to eliminate tree biennial bearing in industrial orchards, fruitlet and fruit thinning is used; this process is costly and ineffective in some cases [2,3]
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