EFFECT OF PARTHENOCARPY ON OVULE DEVELOPMENT IN CUCUMBER (CUCUMIS-SATIVUS L) AFTER POLLINATION WITH NORMAL AND IRRADIATED POLLEN

In nonparthenocarpic cucumber, analysis of the interaction between sea son and female receptivity demonstrated two different modes of fruit d evelopment and seed set. Spring climatic conditions induced significan tly longer ovaries at anthesis with an autonomous fruit set as in natu ral parthenocarpy. Autumn climatic conditions induced smaller ovaries with fruit set influenced by the pollination stage of the female flowe r. These differences involve, during fruit development, a regulation o f the empty seed number especially at both ends of female receptivity period. Indeed, seasons have no effect on ovule receptivity and fertil ity measured by full seed number. It is supposed that priority is give n to seeds with an embryo in the competition for limited maternal reso urces in spring as well as in autumn. In spring, the use of irradiated pollen during the whole female receptivity period did not modify the seed set profile. Moreover, a cytological study of 6-day-old ovules po llinated by irradiated pollen has revealed a similar precocious embryo genesis compared to the control. In cucumber, pollination with irradia ted pollen involves stenospermocarpy rather than 'induced parthenocarp y.' However, we have not been able to determine whether the early abor tive embryogenesis induced by irradiated pollen is gynogenetic or abno rmal zygotic.