Water splash in lieu of fly "pollination" of an invasive plant pathogen in western Oregon

Epichloë typhina (Ascomycetes:Clavicipitaceae) is a plant pathogen infecting the host Dactylis glomerata, orchardgrass. The fungus inhibits developing inflorescences, and is a serious pest concern for grass seed farmers in the Willamette Valley, Oregon's major seed producing region. Epichloë typhina is heterothallic; it must sexually out-cross with an opposite mating type in order to produce ascospores, propagules that infect new hosts. Previous studies have suggested that for sexual outcross to occur, a fly, Botanophila lobata (Diptera:Anthomyiidae), must "pollinate" the fungus during a unique oviposition behavior whereby the fly defecates previously consumed fungal spermatia. However, in the invaded range in the Willamette Valley, the fungus is reported to outcross in absence of fly "pollinators." To test the hypothesis that water splash might replace or supplement B. lobata "pollination" we conducted a greenhouse experiment using caged plants infected with E. typhina. Cages randomly received one of three treatments: water splash between plants, cotton swab between neighboring stromata, or nothing (control). All swab replicates were cross fertilized, while 83.3% and 6.9% of splash and control replicates were cross fertilized, respectively. A chi-square test indicated significant differences in cross fertilization frequency between control and splash, and control and swab treatments, but not between splash and swab treatments (Bonferroni adusted α=0.017). These results suggest that water splash effectively transfers E. typhina spermatia. Heavy spring precipitation, typical of the western Oregon climate, might have contributed to the successful invasion of E. typhina into the region by reducing the importance of fly "pollination."