Flowering dynamics and crossability of different populations of bitter fennel (foeniculum vulgare mill. var. vulgare, apiaceae)

Bitter fennel (Foeniculum vulgare Mill. var. vulgare, Apiaceae) is a hemicryptophyte native to the Mediterranean basin and cultivated for its use as a medicinal and spice. We describe here the flowering dynamics and crossability among six native populations of bitter fennel collected from four localities in Israel, one from Sinai Desert (Egypt), and one from Mersin (Turkey) and grown from under agricultural conditions. Timing and duration of the stigma's receptivity were evaluated morphologically, enzymatically, and by determining fruit set in response to artificial pollination. Self-compatibility rates and crossability within and between populations were also determined in response to artificial pollination. Although the populations initiated flowering at different times through the season, in all cases the stigma's receptivity peaked between six and eight days after anthesis (yellow-bud stage) and lasted for seven days. Pollen can primarily germinate on the stigmata but the stylopodium serves too as a site for pollen germination, albeit at a lower efficiency (0-10% fruit set) as compared to stigmata (25-54%). Although there is complete dichogamy within flowers, umbels, and branches, there in not enough dichogamy between branches, and geitonogamy is therefore possible. A dditionally, all populations displayed a high (0.7-3.7) index of self-compatibility (ISI), indicative of substantial self pollination. Although interbreeding among populations was proven using artificial pollination, geographical isolation and the high likelihood for self-pollination probably restricts gene flow and contributes to the phenotypic diversity observed in wild fennel populations.