INFECTION OF POPULUS-TREMULOIDES BY HYPOXYLON-MAMMATUM ASCOSPORES THROUGH SAPERDA-INORNATA GALLS

Branch galls resulting from oviposition wounds made by Saperda inornat a Say on Populus tremuloides Michx. were studied in relation to inocul ation with Hypoxylon mammatum (Wahlenberg) J.H. Miller ascospores. The natural infection rate of galls in an aspen plantation in central Min nesota 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-yea r period, 9.1% (range 6.5-12.6%) 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 inocul ation of natural wounds on aspen with H. mammatum ascospores.