Strong partial resistance to white pine blister rust in sugar pine

Quantitative resistance to white pine blister rust in 128 controlled- and open-pollinated sugar pine families was evaluated in a “disease garden”, where alternate host Ribes bushes were interplanted among test progenies. Overall infection was severe (88%), but with great variation among and within families: a 30-fold range in numbers of infections per tree, and a 10- fold range in trees with completely inactive, or aborted infections. Inheritance of these partial resistances was strong, with significant amounts of both additive and non-additive genetic variance evident. They will be most useful in combination with major gene resistance (MGR) by reducing the probability of infections virulent to MGR.