Studies on the Stabilization of GA-induced Seedless Berry Production in Muscat Baily A Grapes

I. Variation in Flower Types and its Effect on Seedlessness

Abstract

The variations of flower types and the characteristics of berries derived from each flower type were observed in Muscat Baily A, a hybrid between Baily X Muscat Humburg. The effects of flower type on the GA-induced seedlessness were also observed.
Conversion of flower type was attempted by the prebloom application of 6-benzy-ladenine (BA), which is known to induce sex conversion in male clones of Vitis species.
1. This cultivar usually shows variations in the size of female organs in bloom. So, the flower types were classified into three types: perfect-hermaphroditic flowers (male and female organs develop completely), imperfect-hermaphroditic flowers (male organs are normal but female ones are incomplete), and male flowers (lack of female organs). The frequency of male, imperfect-and perfect-hermaphroditic flowers was proved to fluctuate year to year and by the method of pruning.
2. Removing all male flowers, flowers of each of the remaining two types were retained in each cluster and allowed to set. Imperfect flowers displayed poorer berry set, smaller berry size and more seed number than perfect ones. By GA treatment, perfect flowers produced more seedless berries than imperfect ones.
3. The development of pistil was promoted by BA application 2-3 weeks before anthesis, which increased the frequency of perfect flowers, while by the application 4 weeks before anthesis, the frequency of imperfect ones was increased. The ratio of seedless berry formation was increased by GA in combination with the former BA application, especially remarkable with BA application 2 weeks before anthesiswith 125, 250ppm (above 95 percent), while by GA in combination with the latter, the ratio was decreased.
4. Therefore, it seemed that the occurrence of imperfect flowers is responsible for the ratio in GA-induced seedless berry formation in this cultivar.