VARIABILITY OF VIRULENCE OF NECTRIA-GALLIGENA TOWARDS NORTHERN HARDWOODS

The variability of virulence within a Quebec population of the fungal pathogen Nectria galligena was was studied under greenhouse conditions . Preliminary, small-scale inoculation of Betula alleghaniensis saplin gs confirmed that wounds have to be present for successful infection b y N. galligena and showed that saplings held at 10 degrees C exhibited a broader range in necrotic zone length han saplings held at 24 degre es C for 6 weeks. Results from the inoculation of B. alleghaniensis sa plings with eight full-sib progeny sets of four siblings each of N. ga lligena showed a wide range of virulence in this pathogen. The observe d variability was probably of genetic origin since, in seven cases out of eight, one of the four siblings of a given family was significantl y different from at least one other sibling of the same family. Inocul ation of B. alleghaniensis saplings with a population of 43 isolates o riginating from different host species and geographical locations furt her confirmed the variability of virulence within N. galligena but fai led to indicate a relationship between virulence and host. or geograph ic provenance. Inoculation of six additional deciduous tree species wi th a subset of nine isolates showed the polyphagous character of the p athogen, as lesions of comparable length were generally observed on fi ve of the species tested. None of the nine isolates tested induced any necrosis on Fraxinus americana whereas Quercus macrocarpa tended to b e slightly more resistant than the four remaining true species.