Races of Puccinia menthae in the Pacific Northwest and Interaction of Latent Period of Mints Infected with Rust Races. D. A. JOHNSON, Plant Pathologist, Washington State University, Pullman 99164-6430. D. A. JOHNSON, Plant Pathologist, Washington State University, Pullman 99164-6430. Plant Dis. 79:20-24. Accepted Tor publication 28 September 1994. Copyright 1995 The American Phytopathological Society 20. DOI: 10.1094/PD-79-0020.

Physiologic specialization of Puccinia menthae on various Mentha spp. and the length of latent period on several Mentha spp. infected with isolates of P. menthae were investigated. Eleven races of P. menthae from 17 collections made over a 5-yr period were identified, showing a high degree of physiologic specialization within the P, menthae population. Rust isolates from M. spicata (Native spearmint) infected M. x gracilis (Scotch spearmint) but not M. x piperita (peppermint), and isolates from M. ? piperita infected M. x gracilis but not commercial Native spearmint. A significant interaction for length of latent period was observed between rust isolates and mint genotypes. A significantly longer latent period occurred in M. ? gracilis when infected with rust isolates from M. x piperita than when infected with isolates from M. spicata. Lengths of latent period on M. spicata and M. x gracilis were similar when infected with isolates from M. spicata.