EVALUATION OF SUPERFICIAL CANKER INSTABILITY FOR HYPOVIRULENT CRYPHONECTRIA-PARASITICA INOCULATED ON AMERICAN CHESTNUT TREES

Hypovirulent strains of Cryphonectria parasitica produced superficial cankers on American chestnut (Castanea dentata) chat were unstable for superficiality after one winter. Some unstable cankers yielded C. par asitica isolates that had high virulence on American chestnut trees an d were vegetatively incompatible with che original inoculated hypoviru lent strain, whereas other unstable cankers yielded isolates that had low virulence and were vegetatively compatible with the original hypov irulent strain.