Comparison of berry set between flower clusters formed on primary and secondary shoots of 'Kyoho' grape

摘要

Differences in berry set between primary flower clusters formed on primary shoots and secondary flower clusters formed on lateral shoots of cv. Kyoho grapevines were investigated in studies conducted at Chiba, Japan. Berry set was examined in relation to: (a) developmental stages of florets, pollen and ovaries, (b) activities of pollen tube growth inhibitors in pistils, (c) endogenous plant growth regulators in florets, and (d) pollen tube growth in the pistils. The florets and pistils in secondaryflower clusters at anthesis were smaller than those in primary flower clusters. This difference was related to the suppression of cell division in pericarps in flowers of the secondary clusters. However, there was no significant difference in ovule size. Pollen from florets of secondary flower clusters was smaller, but the percent germination on agar was higher than that from florets of primary flower clusters. The percentage berry set, the number of seeded berries/cluster, and number of seeds/berry insecondary flower clusters were significantly higher than those in primary flower clusters. Compared with florets of secondary flowers, the levels of IAA and cytokinin tended to be higher in florets of primary flower clusters, whereas the levels of GA and ABA were always lower. Water soluble inhibitors of pollen tube growth were higher in pistils of primary cluster florets than in those in the secondary flowers. Thus, the growth of pollen tubes in pistils of primary flower clusters was slower than in the pistils of secondary flower clusters, so that no tube reached the micropyles of ovaries of primary flowers within 24 h after pollination. From these findings, the increase in berry set of secondary flower clusters is attributed to: (1) the low levels of IAA and cytokinin, and (2) high concentrations of ABA and GA in florets and pollen tube growth inhibitors in the pistils.