Influence of Irradiated Pollen on Embryo and Endosperm Development in Kiwifruit

Abstract

Development of seeds following pollination with irradiated pollen was studied inActinidia deliciosa(kiwifruit) ‘Hayward’. Pollinations were carried out using two different sources of pollen (‘Tomuri’ and ‘Matua’) irradiated with gamma rays at doses of 700 and 900 Gy. Non-irradiated crosses were used as controls. Pollen irradiation had little effect onin vitropollen germination. Irradiated pollen affected seed set and seed content, and induced the formation of parthenogenetic embryos. In comparison to the control, the embryo growth rate was slower and the endosperm contained very low amounts of storage products. Seed set was significantly reduced following both doses of irradiation. Two types of seeds were observed: (1) seeds with endosperm only; and (2) seeds with both embryo and endosperm. The proportion of seeds containing endosperm only was almost ten-fold higher than those containing both embryo and endosperm. Embryo production by gamma-irradiated pollen was genotype- and dose-dependent. The induction of parthenogenesis was higher following gamma ray doses of 900 Gy than 700 Gy, which suggests the ‘Hertwig Effect’; the best efficiency was obtained with ‘Tomuri’ pollen. Ploidy level of parthenogenetic embryos was evaluated by nuclear size (area) with the use of image analysis. There was a large difference in embryo nuclei size between control and parthenogenetic embryos (mean size 90.8 and 49.1 μm2, respectively). It is concluded that parthenogenetic embryos represent trihaploids.