Early Inbreeding Depression and Pollen Competition in Calluna vulgaris (L.) Hull.
, Jacquemart A.-L.
Annals of Botany
, 1999. V. 83. No. 6. P. 697–704.
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We investigated whether partial self-sterility in Calluna vulgaris results from abortion of selfed offspring owing to inbreeding depression or a late-acting self-incompatibility mechanism, and whether self-pollen interferes with normal functioning of cross-pollen. Self-pollination resulted in 75% less seed set than cross-pollination. Self-pollen tubes reached ovaries and penetrated ovules as often as those of cross-pollen. Following self-pollination, examination of the size of undeveloped seeds showed that at least 70% resulted from ovule fertilization and arrest of development occurred at various stages. All self-pollinated plants produced seeds and self-fertility varied among plants. These results indicate that the reduced seed set observed in self-pollination is more likely the result of inbreeding depression rather than a late-acting self-incompatibility system. The fecundity component of inbreeding depression was high (0.762). Seed set was reduced by an average of 40% when self-pollen was mixed with cross-pollen, compared to pure cross-pollination. Using genetic markers, we found about 20% of seeds resulted from self-pollination in mixed-pollinated fruits. C. vulgaris is likely to experience self-pollination in nature and our data suggest this will reduce the number of ovules that might otherwise mature after cross-pollination.