Pollination Limitation in a Population of Silene Alba Infected by the Anther-Smut Fungus, Ustilago Violacea

In a population of Silene alba, female plants where all flowers had been handpollinated had more than double the proportion of flowers maturing fruit and number of seeds per fruit compared with control plants, suggesting pollination limitation.

Abstract

SUMMARY (1) In a population of Silene alba, female plants where all flowers had been handpollinated had more than double the proportion of flowers maturing fruit and number of seeds per fruit compared with control plants, suggesting pollination limitation. (2) Hand-pollinated and control plants produced the same number of fruits over the season because hand-pollinated plants produced a smaller total number of flowers, apparently due to limited availability of resources such as energy, water or nutrients. (3) Thirty per cent of the flowering plants in the population produced sterile, sporeproducing flowers because of infection by the anther-smut fungus Ustilago tiolacea; infection can occur following pollinator transport of spores. Eight of the thirty plants in the experiment became infected by U. violacea late in the season; six of these were control plants. Plants that became infected had produced significantly more flowers over the season than plants that remained disease-free.