OBSERVATION OF PARTHENOCARPY IN ACTINIDIA ARGUTA SELECTION 'ISSAI'

The fruiting habit of ‘Issai’ was clarified by comparison with other A. arguta selections. Mature vines of ‘Issai’ (7x), ‘Mitsuko’ (6x), ‘Gassan’ (6x), ‘Nagano’ (4x), ‘Shimane’ (4x), ‘Kochi’ (4x) and ‘Awaji’ (4x, male) were used. Pollen germinability was examined on medium containing 10% sucrose and 1% agar at 20C. To determine self-fruitfulness, flowers were bagged before anthesis and three treatments were imposed: 1) emasculation, 2) self-pollination, 3) cross-pollination with pollen of the male selection ‘Awaji’. All flowers were bagged after treatment. In any selections bearing morphologically hermaphroditic flowers, no pollen germinated. In the male accession ‘Awaji’, the pollen germination rate was 68%. In emasculated and self-pollinated flowers, the rate of fruit set dropped rapidly during the season and no fruit remained on the vine at harvest in any selections except ‘Issai’, whereas cross-pollination with pollen of the male selection ‘Awaji’, resulted in 64–89% of fruit set at harvest. Emasculated flowers of ‘Issai’ did not set fruit. Self-pollination of ‘Issai’ resulted in 30% fruit set at harvest, whereas cross-pollination with ‘Awaji’ caused 65% fruit set. The weight of fruit from self-pollination and cross-pollination with pollen from the male was 4.9 and 5.7 g, respectively. Fruit derived from self-pollination contained no seed, whereas the fruit from cross-pollination contained 23 seed per fruit. These results suggest that ‘Issai’ can set fruit parthenocarpically and its own sterile pollen may have a stimulatory effect on fruit development.