Compatibility Among Host-Specialized Isolates ofHeterobasidion annosumfrom Western North America

Abstract

Harrington, T. C., Worrall, J. J., and Rizzo, D. M. 1989. Compatibility among host-specialized isolates of Heterobasidion annosum from western North America. Phytopathology 79:290-296. Host-specialization of isolates of Heterobasidion annosum from from another 18 trees and stumps in Pacific Coast states also fell into the S California was previously demonstrated by inoculating Pinus ponderosa and P groups based on compatibility; those from diseased pine trees were and Abies concolor (white fir) seedlings in the greenhouse. In the present P-compatible and those from other host genera were S-compatible. study, 18 of these isolates were tested for sexual compatibility in hetero- However, compatibility of isolates and strains from stumps with S and P karyon-homokaryon pairings with six S and four P tester strains of H. testers was not consistent with the host genus, indicating that stump annosum from Europe representing two intersterility groups. colonization can be non-host specific. When North American strains were Compatibility was determined by the presence of clamp connections in paired among themselves or with heterokaryotic isolates, the two subcultures from the homokaryotic tester mycelia taken 5 wk after pairing, compatibility groups were less evident than when European strains were The nine isolates specialized to fir seedlings were compatible with S testers, used. Reports thus far suggest that both the S-compatible and Pand the nine isolates specialized to pine seedlings were compatible with P compatible groups are widespread in western North America, but only the testers. Some P-compatible isolates formed clamps with a few S testers. P group has been reported in eastern North America. Heterokaryotic isolates and homokaryotic (single-basidiospore) strains