Inheritance of the bark reaction resistance mechanism in Pinus monticola infected by Cronartium ribicola

Necrotic reactions in branch or main stems of western white pine (pinus monticola Dougl.J caused by infection by the blister rust fungus (Cronartium ribicola J. C. Fisch. ex Rabenh.) are a maJ'or mechanism of resistance. Overall, 26 percent of the seedlings eliminated the fungus via this defense system. Heritability based upon crossing family groups averaged 33 percent for three sets of crossing groups. Heritability based upon individuals averaged 4 percent. The largest genetic advance (selected population compared to the original population before introduction of blister rust) could be made by selecting the average family out of the plus tree selection group. Moderate gains can be made just by selecting the best family. A small but significant gain can be made by selecting seedlings within families. Several breeding methods are discussed concerning the use of bark reaction resistance in new cultivars of western white pine.