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The genetics of disease interaction in the lodgepole pine : western gall rust host : parasite system Schulting, Maureen Joan


One hundred and eighty, three year old lodgepole pine (Pinus contorta var. latifolia Dougl.) seedlings, representing eighteen half sibling families were each inoculated with five different spore sources of western gall rust (Endocronartium harknessii (J.P. Moore) Hiratsuka) in June 1985 to investigate the genetics of disease interaction in this host:parasite system. Possible early symptoms of infection were recorded fourteen days after inoculation. Tabulations of the number of galls per shoot and shoot length were made in September 1985 and June 1986. Fifty-two percent (567 out of 1088) of the inoculated shoots became infected. The mean number of galls per infected shoot was 3.33. Statistical analyses indicated that only horizontal (quantitative) resistance was present in the lodgepole pine -western gall rust pathosystem. The lodgepole pine half sibling families and seedlings varied greatly in their horizontal resistance. The variation in levels of resistance found in lodgepole pine will allow for a successful western gall rust resistance breeding program. The number of galls per tree for the female parent trees did not significantly correlate with the percentage of shoots infected on the half-sibling progeny. Hence, tree breeders will have to test the resistance of progeny. Red staining was found more frequently on shoots that became infected suggesting that red staining is a possible early symptom of infection by western gall rust.

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