Improving 'bing' Sweet Cherry Fruit Quality with Plant Growth Regulators

Final fruit diameter is the prime determinant of sweet cherry value. Previous research has shown that mesocarp cell size accounts for most variability in fruit size within a genotype. Our research program is now evaluating the potential to improve sweet cherry fruit size/weight with growth regulators. In the current study we screened 8 plant growth regulators and their combinations for their ability to increase ‘Bing' fruit weight. Each treatment was applied in lanolin paste directly to fruit pedicels at 9 and 30 days after full bloom, to coincide with estimated peak in cell division and onset of cell expansion activity, respectively. During the cell division stage, several cytokinins improved fruit weight significantly (ca.+15%) with N-(2-Chloro-4-pyridyl)-N'-phenylurea (CPPU) at 100 mg l-1 being the best. Auxin treatments were ineffective at improving fruit quality but several GA treatments improved fruit size significantly. GA3 at 200 mg l-1 during the cell division stage was the most effective and improved final fruit weight by 15%. From this treatment, 60% of the fruit were ≥9 g compared to just 15% of similar weight fruit from untreated limbs. These results are consistent with the previous study of applications at full bloom and show promise for early applications of GA3 to improve sweet cherry fruit quality. Furthermore, while single applications of GA1 or CPPU during fruit expansion did not increase fruit weight, their combination increased fruit weight by 19%. More than 80% fruit fall into the category of ≥ 9 g. Results of large-scale orchard trials will also be discussed.