Host range of Polymyxa betae Keskin strains in rhizomania-infested soils of sugar beet fields in Japan.

Abstract

Host range of Polymyxa sp. isolated from various plants grown in rhizomania-infested soils of three different localities in Hokkaido was compared. Among 108 species of plants belonging to 23 families tested, 12 plants belonging to Chenopodiaceae, Amaranthaceae and Portulacaceae were infected with the fungus. The other 20 families including Gramineae were not infected. All isolates of Polymyxa sp. were identified as Polymyxa betae Keskin on the basis of their host range and morphological characteristics. The host range of the isolates was found to be limited to the family of the original host. Among the Chenopodiaceous isolates, that from sugar beet did not infect Chenopodium album, and those from C. album did not infect sugar beet. These P. betae isolates could be divided into several formae speciales; Amaranthus retroflexus isolates were identified as P. betae Keskin f. sp. amaranthi Barr, for the Portulaca oleracea isolates a new forma specialis P. betae Keskin f. sp. portulacae was proposed. Although sugar beet isolates and C. album isolates should be divided into different formae speciales, respectively, the classification of these isolates should await comparison with the Canadian isolate from C. album. From these results it is suggested that sugar beet isolates of P. betae which have a high infectivity to Beta vulgaris are associated with the incidence of rhizomania of sugar beet whereas the other two formae speciales and C. album isolates may not be involved.