ALLELOPATHIC POLLEN EXTRACT FROM PHLEUM-PRATENSE L (POACEAE) REDUCES GERMINATION, IN-VITRO, OF POLLEN OF SYMPATRIC SPECIES

In vitro studies were performed to quantify the putative allelopathic effect of pollen from Phleum pratense (Aveneae: Poaceae). Extract from ground pollen was partitioned, using ion-exchange chromatography. Aci dic, basic, and neutral fractions were isolated. These fractions, alon g with extract from intact pollen, were applied in increasing concentr ations of the equivalent of 0 (control), 0.1, 1, 3, 5, 10, and 25 poll en grains of P. pratense/mu L. Pollen from five sympatric, wind-pollin ated species of Poaceae and P. pratense was germinated on agar medium that contained different extract concentrations. In response to increa sing extract concentrations, from intact pollen or from acidic fractio ns, mean percentage of germination of pollen of Agropyron repens, Brom us inermis, Danthonia compressa, and Poa compressa decreased in a nonl inear manner. Basic, neutral, and solvent fractions did not show any a llelopathic activity; hence, the allelochemicals may be acidic in natu re. An extract concentration equivalent to 0.1 grains/mu L was suffici ent to inhibit pollen germination in these four species. Hence pollen allelopathy requires fewer pollen grains than may exist on foreign sti gma in situ. Pollen from P. pratense was not autotoxic. This, together with the lack of a pollen-allelopathic effect on the contribal Agrost is stolonifera, indicates that members of the Aveneae may be able to d etoxify the pollen allelochemicals. Similar experiments, using extract s from intact pollen from 11 populations of Phleum across eastern Cana da revealed that the pollen-allelopathic effect on sympatric populatio ns of Agropyron repens was consistent, save for the lone population of Phleum arenarium. Allelopathic pollen may occur in most populations o f P. pratense in eastern Canada but not in P. arenarium.