Infection of Populus tremuloldes by Hypoxylon mammatum ascospores through Saperda inornata gails

Abstract

Branch galls resulting from oviposition wounds made by Saperdainornata Say on Populustremuloides Michx. were studied in relation to inoculation with Hypoxylonmammatum (Wahlenberg) J.H. Miller ascospores. The natural infection rate of galls in an aspen plantation in central Minnesota averaged 1.6% (range 0.8–2.6%) during a 4-year period. However, when S. inornata galls were inoculated with ascospores during a 3-year period, 9.1% (range 6.5–2.6%) of the branches became infected. When galls were inoculated with sterile water, 3.3% of the branches became infected, perhaps indicating that inoculum already was present in the galls. The average elapsed time from ascospore inoculation until the development of hypoxylon canker symptoms was 26 months. These results provide the first demonstration of canker development following inoculation of natural wounds on aspen with H. mammatum ascospores.