Regulation of crop load and quality in sweet cherry cv. ‘Sweet Heart’ using blossom thinning

Self-fertile cultivars of sweet cherry (Prunus avium) produce heavy crop load that is often associated with small and poor-quality fruits. Therefore, a crop load-management strategy is required to improve the quality of the fruit. In this study, the effect of blossom thinners on fruit set, yield and quality of the fruits was evaluated. Three types of blossom thinners were used at three different concentrations viz., ammonium thiosulphate (ATS) (1, 1.5 and 2%), naphthaleneacetic acid (NAA) (20, 40 and 60 ppm) and corn oil emulsion (1, 2 and 3%). These were sprayed at 80% of the bloom stage. The vegetative, flowering, fruit set and yield parameters were observed and recorded. Fruit quality was evaluated by measuring the physical and chemical characteristics of the fruits at the harvest stage. Negative correlation was found between fruit set and quality of fruit. The reduction in the crop load was associated with enhanced vegetative growth, including higher leaf:fruit ratio, higher supply and availability of photosynthates to the remaining fruitlets and reduced fruit firmness and titratable acidity. Fruit size, weight, volume, hue value, chroma value, soluble solid content (SSC), total sugars, SSC/acid ratio, anthocyanin and ascorbic acid content were enhanced as a result of thinning. The foliar spray of ATS at 2% and NAA at 60 ppm, at 80% bloom proved to be the most effective in reducing crop load and enhancing the fruit quality.