Potential for outcrossing in an apparently asexual population of Fusarium circinatum, the causal agent of pitch canker disease

Abstract

Fusarium circinatum (teleomorph = Gibberella circinata) is responsible for the current epidemic affecting pine trees in native and urban forests along California's central coast. Only eight vegetative compatibility groups have been recovered from samples collected throughout the pathogen's range in California. This low level of diversity is suggestive of an asexually propagating population. However, crosses conducted in the laboratory on carrot agar, as well as on Monterey pine (Pinus radiata) twigs, reveal that California strains of the fungus are capable of undergoing sexual reproduction. Outcrossing was confirmed by demonstrating vegetative incompatibility between the progeny and their parents. These results indicate that sexual reproduction is possible within the California population of the pitch canker pathogen.

Key Words:

• forest pathology
• fungal pathogen
• Gibberella circinata
• Pinus radiata