Fungi associated with the pistillate flowers of white oak (Quercus alba L.) and their effect on pollen germination

Three genera of the Fungi Imperfecti (Alternaria, Cladosporium and Epicoccum) were isolated in high frequency from the pistillate flowers of white oak. These genera occur worldwide and although several species of each genera are parasitic on crop plants, they are primarily saprophytic in the forest ecosystem. Of the three genera, only Cladosporium is parasitic on Q. alba, causing a leaf mold. Several other genera of fungi were isolated in low frequency from the oak flowers. Included in this group were Penicillium, Pestalotia, Curvularia, Pyrenochaeta, Nigrospora and Fusarium.

The effect of fungal spores on pollen germination was investigated. Suspensions of pollen grains and fungi spores were cultured in Van Tieghem cells. Pollen germination in vitro was significantly enhanced by Cladosporium and Epicoccum, but unaffected by Alternaria.