IN-VITRO ALLELOPATHIC EFFECTS OF POLLEN FROM 3 HIERACIUM SPECIES (ASTERACEAE) AND POLLEN TRANSFER TO SYMPATRIC FABACEAE

Pollen allelopathy occurs when pollen toxins inhibit sexual reproducti on in heterospecifics. To quantify pollen allelopathic effects in vitr o, pollen of Hieracium aurantiacum, H. floribundum, and H. pratense wa s extracted with double distilled water into concentrations of 0 (cont rol), 0.1, 1, 3, 5, 10, and 25 pollen grains/mu l. A subset of these e xtracts was partitioned by ion-exchange chromatography into acidic, ba sic, and neutral fractions. Pollen from six sympatric species of Fabac eae (Lotus corniculatus, Medicago sativa, Trifolium hybridum, T. prate nse, T. repens, Vicia cracca) and the species of Hieracium was germina ted on agar media containing different extract concentrations. As extr act concentrations from intact pollen or from acidic fractions increas ed, mean percent germination of pollen of all Fabaceae decreased nonli nearly. Extract concentrations of 0.1 grains/mu l and above inhibited pollen germination in the Fabaceae. In no case was any Hieracium speci es affected, i.e., there was no autotoxicity. Similar results were obt ained using plants from nine populations of H. floribundum and H. prat ense across eastern Canada. Observation of floral visitors indicated t hat there were relatively few movements between Hieracium and the Faba ceae (about 15% of total visits). Hence there is limited opportunity f or heterospecific pollen transfer. This was consistent with censuses o f stigma, i.e., few pollen grains of Hieracium were found on stigma of the Fabaceae. Thus, pollen allelopathy in Hieracium is unlikely to af fect reproductive success in these six species of Fabaceae.