Temperature Sensitivity of Reactions ofPopulusspp. to Races ofMelampsora larici-populina

Abstract

Hypersensitive-type local necrotic reactions in the differential poplar (P. deltoides) clones ''7-2'', ''7-9'' and ''7-13'' were more pronounced to physiologic races A, B, D and E of M. larici-populina at 12.degree. and 25.degree. than at 20.degree. C. The response of the congenial clones P. .times. euramericana ''I-214'', ''I-488'', ''65/27'' and P. nigra ''Evergreen'' inoculated with the same races and incubated at similar temperatures was clearly temperature sensitive. Incubation period for the development of flecking was longer and numbers of uredia per leaf disk were higher when cultivar-race combinations were incubated at 12.degree. and 20.degree. than at 25.degree. C. The significant 2nd- and 3rd-order interactions of incubation temperature, cultivar and race suggest that the temperature sensitivity of cultivar/race reactions could maintain racial diversity in pathogen populations despite cultivar selection pressure.