Genetic evidence that butternut canker was recently introduced into North America

Abstract

Butternut (Juglans cinerea) is seriously threatened by a canker disease caused by Sirococcus clavigignenti-juglandacearum, a fungus with no known sexual stage. This pathogen was first reported in 1967 and is now found throughout the native range of butternut, suggesting that it was introduced into North America. We used randomly amplified polymorphic DNA (RAPD) markers to examine genetic variation in S. clavigignenti-juglandacearum over a large portion of the native range of butternut. The 55 RAPD fragments were all found in all 86 isolates of the fungus. This complete monomorphism is consistent with the fungus having been introduced into North America as a single isolate and suggests that if resistant butternut genotypes are found, the pathogen will not likely be able to rapidly evolve genotypes that can attack them.Key words: Sirococcus clavigignenti-juglandacearum, Juglans cinerea, RAPD, randomly amplified polymorphic DNA.