Potential diversity in vegetative compatibility groupings in the California population of Gibberella circinata

Pitch canker, caused by Gibberella circinata, is a disease affecting pines throughout the world. Although the pathogen is capable of sexual reproduction, natural populations are often comprised of very few vegetative compatibility groups (VCGs), which implies a predominance of asexual reproduction. However, even where outcrossing occurs, a population could have limited VCG diversity due to a low level of polymorphism at the loci governing vegetative compatibility (= vic loci). To determine whether this was the case for the California population of G. circinata, inter-fertile strains were crossed under laboratory conditions. Progeny of this cross included a minimum of 29 VCGs, which was consistent with segregation of vic alleles at five loci. Only two of these VCGs were known to occur naturally in California. Three VCGs accounted for 32.4 % of the progeny but 0 % of the California population. Overall, the results support the conclusion that outcrossing has been rare or absent in the California population of G. circinata.