Differential ovule development following self‐ and cross‐pollination: the basis of self‐sterility in <i>Narcissus triandrus</i> (Amaryllidaceae)

Self‐pollination results in significantly lower seed set than cross‐pollination in tristylous Narcissus triandrus. We investigated structural and functional aspects of pollen–pistil interactions and ovule–seed development following cross‐ and self‐pollination to assess the timing and mechanism of self‐sterility. Ovule development within an ovary was asynchronous at anthesis. There were no significant differences in pollen tube behavior following cross‐ vs. self‐pollination during the first 6 d of growth, regardless of style morph type. Double fertilization was significantly higher following cross‐ vs. self‐pollination. Aborted embryo development was not detected following either pollination type up to seed maturity. Prior to pollen tube entry, a significantly greater number of ovules ceased to develop following self‐ vs. cross‐pollination. These results indicate that self‐sterility in N. triandrus operates prezygotically but does not involve differential pollen tube growth typical of many self‐incompatibility (SI) systems. Instead, low seed set following self‐pollination is caused by a reduction in ovule availability resulting from embryo sac degeneration. We hypothesize that this is due to the absence of a required stimulus for normal ovule development. If this is correct, current concepts of SI may need to be broadened to include a wider range of pollen–pistil interactions.