VIEW ARTICLE

Resistance

Temperature Sensitivity of Reactions of Populus spp. to Races of Melampsora larici-populina. M. Chandrashekar, Graduate student, Department of Forestry, Australian National University, P.O. Box 4, Canberra A.C.T. 2600, Australia; W. A. Heather, reader, Department of Forestry, Australian National University, P.O. Box 4, Canberra A.C.T. 2600, Australia. Phytopathology 71:421-424. Accepted for publication 16 July 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-71-421.

Hypersensitive-type local necrotic reactions in the differential poplar (Populus deltoides) cultivars '7-2,’ ‘7-9’ and '7-13,’ were more pronounced to physiologic races A, B, D, and E of Melampsora larici-populina at 12 and 25 than at 20 C. The response of the 'congenial cultivars' P. × 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 and 20 than at 25 C. The significant second- and third-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.