Characteristics of seedless berries of triploid hybrid grapes (Vitis complex) from reciprocal crosses between diploid 'Muscat Bailey A' and tetraploid 'Red Pearl'

To evaluate fruit quality of triploid hybrid grapes obtained from reciprocal crosses between diploid 'Muscat Bailey A' and tetraploid 'Red Pearl', the flower clusters were immersed in a solution of GA ₃ (100 mg/liter) at the full bloom stage and examined at the mature stage. Fruit set was observed in 55% of the 3x hybrids from 'Muscat Bailey A' X 'Red Pearl' and 68% of those from the reciprocal. GA ₃ treatment resulted in fruit set in all the hybrids. GA ₃-treated flower clusters of hybrids that showed no fruit set without GA ₃ treatment set fruits with the average of 67 berries per cluster. In almost all hybrids that set fruits, GA ₃ treatment increased the number of berries set per cluster remarkably, especially in those set small number of berries without GA ₃ treatment. In hybrids that showed no fruit set without GA ₃ treatment, average berry weight in GA ₃-treated clusters ranged from 1 to 3 g with the average of 1.9 g. In almost all hybrids that set fruits without GA ₃ treatment, GA ₃ treatment to the flower clusters increased berry weight irrespective of that in non-treated flower clusters. In non-treated clusters, fertilized seeds were rarely detected in a few berries of hybrids from the reciprocal crosses (<0.3% per berry), whereas in GA ₃-treated clusters the rates of berries with seeds decreased less than 0.1%. In non-treated clusters, a large number of unfertilized small seeds with hard seed coat (< 0.4 small seed per berry in average) were often observed among the hybrids from the reciprocal crosses. In GA ₃-treated clusters, the rate of small hard seeds in each hybrid was dramatically decreased less than 0.1 seed per berry. About 95% of hybrids showed moderate and low extent of lignification of pedicles in GA ₃-treated clusters. Berry cracking was scarcely observed among the hybrids from the reciprocal crosses.