Co-application of gibberellin and copper sulphate reduces number of seeds as innovative technique for alleviating alternate bearing in Balady mandarin

TL;DR

Spraying Balady mandarin trees with gibberellin and copper sulphate reduces seeds and improves fruit quality, helping to prevent alternate bearing.

Contribution

A novel technique combining gibberellin and copper sulphate to reduce seed count and alleviate alternate bearing in mandarin trees.

Findings

Combined GA and CuSO4 reduced seeds by 35.48% and 37.22% and improved fruit weight and yield.

Endogenous GA levels in leaves decreased by 16.48% and 22.2% with the treatment.

The treatment improved Off year yield by up to 107.7% through increased fruit numbers.

Abstract

Seeds are regarded as a source of gibberellins (GA) which promote fruit set, fruit growth and plant growth. However, trees with more-seeded fruits tend to alternate bearing (AB) due to high gibberellins supplies. So, this investigation aimed to reduce number of seeds via spraying with 1000 ppm GA or copper sulphate (0.1% CuSO4) or 1000 ppm GA + 0.1% CuSO4 twice during flowering as a new technique to alleviate AB in Balady mandarin tree. Generally, individual spray of GA or CuSO4 reduced number of seeds per fruit and AB. Also, the combined application of GA + CuSO4 recorded the lowest significant number of seeds by 35.48% & 37.22% and fruit set by 27.6% & 25%, meanwhile, it recorded the highest increase percentage of fruit weight (32.2% & 37.2%) and marketable yield (17.7% & 28.17%) compared to the control in the two On year seasons. In addition, this treatment recorded the lowest concentration of endogenous GA in leaves of mandarin trees (7.6 & 7 µg/g F.W.) with the highest reduction percentage of 16.48% & 22.2% in comparison to the control (9.1 & 9 µg/g F.W.) in both seasons, respectively. Thus, this treatment reduced endogenous GA levels by 16.48% & 22.2% and AB index by 55.4% & 50.7% in both seasons. Furthermore, in the following two Off seasons, GA + CuSO4 improved fruit weight by 2.4% & 16.7%, number of fruits by 76.7% & 97.7%, and yield by 58.3% & 107.7%, in both seasons, respectively. Accordingly, GA + CuSO4 proved to be efficient treatment which effectively reduced endogenous GA in leaves of mandarin trees, produced low-seeded fruits (high quality fruits), reduced AB index and improved On year yield via increasing fruit weight and the following Off year yield via increasing fruits number per tree.

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