Embryo sac development and fruit set of 'Satohnishiki' sweet cherry as affected by temperature, GA(3) and paclobutrazol

Effects of temperature and endogenous and exogenous gibberellins (GA) on em bryo sac development and fruit set of 'Satohnishiki' sweet cherry were stud ied. Trees were grown in sunlit growth chambers kept at 15 degreesC and 25 degreesC from one month before anthesis to petal fall. At 25 degreesC, the nucelli and embryo sacs degenerated more rapidly than at 15 degreesC. When flowers were hand-pollinated with pollens of 'Takasago', fruit set was sign ificantly lower at 25 degreesC than at 15 degreesC. Flowers which developed at 25 degreesC had a higher endogenous gibberellin level than had those at 15 degreesC. When bursting buds were sprayed with 10 and 100 ppm GA(3), th e percentage of ovules with degenerated embryo sac or nucellus increased co nsiderably by 2 days after anthesis. But an application of paclobutrazol (P BZ) to bursting buds prolonged embryo sac longevity and increased fruit set . These results indicate that the endogenous GA may: 1) regulate the develo pment of the nucellus and embryo sac in sweet cherry flowers, and 2) induce early embryo sac degeneration, which results in the low fruit set during p eriods of high temperature.