Optimizing preharvest application rate of gibberellic acid (GA₃) and homobrassinolide (HBR) to improve shipping quality of sweet cherry (Prunus avium L.)

The objectives of this research were to evaluate the effects of GA₃ application rates (25, 50, and 100 ppm) and a new compound homobrassinolide (HBR) (1 ppm) on harvest and shipping quality of three late-season cultivars grown in the US Pacific Northwest. Foliar applications of GA₃ were applied to 'Lapins' and 'Sweetheart' and HBR to 'Sweetheart' and 'Skeena'. All treatments were applied at straw color. Fruit were harvested when they attained a predetermined CTIFL color score: 'Lapins' at ~5; 'Sweetheart' and 'Skeena' at ~4. Results demonstrated that GA₃ increased FF, reduced pitting susceptibility and limited stem browning (SB) after cold storage for 'Lapins' and 'Sweetheart'. The improved FF and shipping quality, however, did not follow a rate response to GA₃ and was optimized at 25 ppm. GA₃ delayed harvest timing (slowed color development), but the harvest delay did not correspond to improvements in fruit size for either cultivar. GA₃ had no consistent effect on soluble solid content (SSC%), titratable acidity (TA%), skin darkening, or moisture loss (ML%) for either cultivar at harvest or following 4 weeks of storage at 0°C. HBR at 1 ppm increased FF of 'Sweetheart', but did not affect fruit color, fruit size, SSC, TA, pitting susceptibility, skin darkening, SB, or ML of 'Sweetheart' and 'Skeena' at harvest or following 4 weeks of storage at 0°C. Positive effects of HBR on FF warrant greater evaluation.