Influence of irradiated pollen on embryo and endosperm development in kiwifruit

Development of seeds following pollination with irradiated pollen was studi ed in Actinidia 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 us ed as controls. Pollen irradiation had little effect on in vitro pollen ger mination. Irradiated pollen affected seed set and seed content, and induced the formation of parthenogenetic embryos. In comparison to the control, th e embryo growth rate was slower and the endosperm contained very low amount s of storage products. Seed set was significantly reduced following both do ses of irradiation. Two types of seeds were observed: (1) seeds with endosp erm only; and (2) seeds with both embryo and endosperm. The proportion of s eeds containing endosperm only was almost ten-fold higher than those contai ning both embryo and endosperm. Embryo production by gamma-irradiated polle n was genotype- and dose-dependent. The induction of parthenogenesis was hi gher following gamma ray doses of 900 Gy than 700 Gy, which suggests the 'H ertwig Effect'; the best efficiency was obtained with 'Tomuri' pollen. Ploi dy level of parthenogenetic embryos was evaluated by nuclear size (area) wi th 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 mu m(2), respectively). It is concluded that parthenogenetic embryos repres ent trihaploids. (C) 1998 Annals of Botany Company.