Self-incompatibility and Time of Stigma Receptivity in Two Species of Hydrangea

in HortScience

The objectives of this study were to evaluate self-incompatibility in Hydrangea paniculata Sieb. and H. quercifolia Bartr. and to determine optimum time for pollination of these two species. Flowers from three genotypes of each species were collected 1, 2, 4, 8, 24, 48, and 72 hours after cross- and self-pollination, stained with aniline blue and observed using a fluorescence microscope. In both species, pollen germination was observed on stigmas of over half of the flowers collected 4 to 72 hours after cross- or self-pollination. Differences in pollen tube length between cross- and self-pollinated flowers were noted from 8 to 72 hours after pollination in H. paniculata and from 24 to 72 hours after pollination in H. quercifolia. By 72 hours after pollination, most self-pollen tubes had only penetrated the top third of the style but cross-pollen tubes had grown to the base of the style and entered 40% to 60% of the ovules. Stigmas of H. paniculata were receptive to pollen from anthesis to 5 days after anthesis, while stigmas of H. quercifolia were receptive from 1 to 5 days after anthesis. This study provides evidence of a gametophytic self-incompatibility system in H. paniculata and H. quercifolia. Occasional self-seed set previously observed in these species was theorized to have been due to pseudo-self compatibility.

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