Effects of Different Fruit Set Enhancement Treatments on Fruit Set Rate and Fruit Quality of the Self-Compatible Sweet Cherry Cultivar ’Sunburst’ under Protected Cultivation

Sweet cherries are an important temperate fruit crop, and the area under protected cultivation has continued to expand in recent years. However, the instability of fruit set rates under protected conditions is particularly pronounced, and the adoption of fruit-setting aids has become common practice in commercial production to stabilize and improve fruit-set performance. Various fruit-setting measures, including biotic pollination and hormonal induction, have been shown to regulate source-sink relationships through different physiological pathways, thereby significantly influencing fruit set rates and fruit quality. In this study, three fruit-setting treatments were applied: hand pollination (HP), plant growth regulator treatment (PGRT), and bee pollination (BP), with an untreated control (CK) included for comparison, to evaluate their effects on fruit set rate and fruit quality in the self-compatible sweet cherry cultivar ’Sunburst’ under protected cultivation. Both HP and PGRT significantly increased the fruit set rate, and fruit firmness and raffinose content were also enhanced. However, significantly elongated pedicels and elevated gluconic acid content were observed under PGRT, suggesting that normal organic acid metabolism may have been disrupted by this treatment. Although BP was associated with relatively high total phenolic content, the fruit set rate remained low and did not differ significantly from that of the control (CK). Comprehensive evaluation indicated that, whilst ensuring adequate fruit set, hand pollination exerted the most favourable effect on overall fruit quality and was identified as the optimal green supplementary fruit-setting measure for protected sweet cherry production.