Self-pollination, style length development and seed set in self-compatible Asteraceae: evidence from <i>Senecio vulgaris</i> L.

<b><i>Background</i></b>: Variation in style length has been reported in <i>Senecio vulgaris</i> and has been associated with outcrossing rate. <b><i>Aims</i></b>: To determine if (i) long styles lack germinated pollen on stigmas left to self-pollinate, (ii) successful self-pollination causes styles to stop elongating and shrink in length and (iii) seed set increases with the amount of pollen deposited on stigmas. <b><i>Methods</i></b>: Determined germinated self-pollen on stigmas of long and short styles after auto-self-pollination; scored style length over 48 h in self-pollinated and non-pollinated florets; recorded seed set after placing different amounts of pollen on stigmas. <b><i>Results</i></b>: Most long-styled florets had zero or low amounts of germinated pollen on stigmas in contrast to most short-styled florets. Styles initially elongated to the same length in self-pollinated and non-pollinated florets, then shrank in length in self-pollinated florets while continuing to elongate in non-pollinated florets. Seed set increased with number of pollen grains deposited on stigmas. <b><i>Conclusions</i></b>: Successful self-pollen deposition and/or germination on stigmas of <i>S. vulgaris</i> are indicated by presence of short styles, whereas the opposite is indicated by presence of long styles in florets left to self-pollinate. Self-pollination causes styles to shrink after initially elongating. Seed set is dependent on the amount of pollen deposited on stigmas.