Hypo-virulent Cryphonectria parasitica and distribution/infection factors in southern Appalachia.

Abstract

Prior to its decline and functional extinction due to an invasive blight fungus (Cryphonectria parasitica) in the early 20th century, the American chestnut was a key dominant tree species in most eastern deciduous forests. The infection mechanism, and associated factors affecting rates of infection, must be understood if a hybrid chestnut species is to be reintroduced within native range tree stands. The focus of our work was on on the blight fungus itself. Our objectives were to: 1) determine the possibility of hypo-virulent (or less infectious) strains of the fungus being present at our research site, 2) identify factors correlated with infection rates at the site, and 3) examine possible connections between infection and chestnut mortality rates and factors like chestnut type, family, and site location. We sampled each of four types of chestnut (Pure American/Chinese and two hybrids [B3F2 and B3F3]) at the St. George research site where we characterized cankers and tree environment in addition to culturing canker samples under lab conditions. We did not find evidence of hypo-virulent strains of the chestnut blight at the research site, which could be attributed to hypo-virulent fungus having relatively low success rates due to inhibited sporulation. There was no significant relationship between chestnut species/lineage and infection/mortality rates. This research could inform the development and success of hybrids used in the reintroduction of American chestnut in the future.