Western white pine (Pinus monticola) populations have been decimated by an invasive fungal pathogen that causes white pine blister rust (Cronartium ribicola). White pines host diverse fungal endophyte communities which have been associated with reduced severity of blister rust disease. Some fungal endophytes produce defensive compounds that inhibit the growth and survival of pathogens. If these defensive compounds can inhibit growth and survival of the pathogen C. ribicola, they may also have potential to decrease blister rust damage in infected white pines.
We isolated hundreds of fungal endophytes from healthy white pines throughout the Pacific Northwest. We also acquired fungal isolates associated with disease resistance from previous white pine common garden surveys. Fungi were grown in liquid media for several weeks before all secondary compounds were extracted and sterilized. The C. ribicola pathogen and other phytopathogens were isolated from needle spots of infected white pines. We then used microspectrophotometry and a fluorescent cell viability indicator to monitor changes in pathogen metabolism when exposed to each endophytic compound.
Results/Conclusions
The compounds exhibited a range of inhibitory effects on C. ribicola metabolism in vitro. Compounds extracted from entomopathogenic fungi showed the largest inhibitory effect by reducing the cell viability of C. ribicola up to 30% and needle cast pathogen, Elytroderma deformans up to 60%. These entomopathogens are commonly found in soil and have shown inhibitory effects against phytopathogens of several plant species. In previous experiments, we found evidence of a negative correlation between entomopathogenic fungi and the number of needle spots and cankers present on whitebark pine (Pinus albicaulis) seedlings. Overall, our results suggest that white pine endophytes may be a critical resource for fighting white pine blister rust disease.