We studied the effects of GA (GibberellinA 3 ; KYOWA Co. Ltd.) treatment on parthenocarpic seedless berry formation and cytokinin-like plant growth regulator CPPU (Forchlorfenuron; KYOWA Co. Ltd.) treatment on berry enlargement in Japanese wild grape, Vitis coignetiae Pulliat. The goal of our research is the development of stable fruit production, inducing parthenocarpy by chemical control in a single variety orchard of female trees. Two adult vines of the same strain in the orchard of Yamagata Field Science Center at Yamagata University were used to elucidate the optimal times and concentrations for these treatments. Two GA treatments of a cluster bagged during flowering against pollination at the beginning of flowering (100 ppm) and after flowering (50, 100 or 200 ppm on 5, 10 or 15 days after full bloom) led to 99% seedless berry formation; however, the parthenocarpic seedless berries formed were quite smaller and had a lower soluble solid concentration and higher organic acid content than normal seeded berries. We next examined the effects of CPPU treatment on seedless berry enlargement. When treatment with 100 ppm CPPU at full bloom, 5, 10 and 15 days after full bloom, was applied, the earlier the treatment, the larger the number of berries per fruit cluster. When dipping treatment of the fruit cluster in 50, 100 or 200 ppm CPPU solution 10 days after full bloom was tested, a significant berry weight increase was observed only with treatment at 100 ppm, although the berry quality remained lower than that of seeded berries. These results showed the optimal times and concentrations of GA and CPPU treatment for obtaining seedless berries from the strain of Vitis coignetiae in a single variety orchard of female trees, but further studies are needed to obtain larger berries of better quality.
To stabilize the berry production in a dioecious Japanese wild grape, Vitis coignetiae Pulliat, we studied the flowering patterns in female and male plants and the effects of timing and frequency of artificial pollination on fruit set and berry quality. The flowering periods of female and male plants were ten and nine days, respectively. The highest fruit set in the fruit cluster (54.6%) after performing artificial pollination twice was obtained using the pollen of male plants on the second and fifth days of the flowering period. With a single artificial pollination, we obtained higher fruit set with pollination on the fifth day (46.2%) than with pollination on the second day (24.0%). The soluble solid concentration in berry juice was higher in fruit with pollination on the fifth day. We also found it useful to use pollen from Vitis cultivars with artificial pollination to obtain a high percentage of fruit set in Vitis coignetiae Pulliat.
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