Interactions with hosts at cool temperature, not cold tolerance, explain the unique epidemiology of Ralstonia solanacearum Race 3 biovar 2. F. MENG (1), A. Milling (1), C. Allen (1)
(1) Dept. Plant Patholoygy, UW-Madison, Madison, WI
Phytopathology 98:S104

Abstract: Most strains of the bacterial wilt pathogen Ralstonia solanacearum are tropical, but one group, R3bv2, can attack plants in temperate zones and highland tropics. Extensive epidemiological data document the destructiveness of R3bv2 in cooler climates, but the basis of this distinctive ecological trait is not understood. We compared the survival, growth and virulence of two R. solanacearum strains, GMI1000 (race 1, tropical) and UW551 (R3bv2, temperate) at different temperatures with and without host plants. At 4C (the temperature of commercial seed potato storage), neither GMI1000 nor UW551 survived more than 90 days in water. However, UW551 survived more than 4 months in inoculated potato tubers at 4C, while GMI1000 survived less than 50 days in tubers. The two strains grew similarly in minimal media at 20C and 29C. At 29C, both strains wilted tomato plants rapidly in a naturalistic soil-soak virulence assay. In contrast, at 20C UW551 was much more virulent on tomato than GMI1000. Thus, there was little difference in growth and survival of tropical and R3bv2 strains at 4C, 20C, or 29C in the absence of a plant host. But at cooler temperatures R3bv2 survived longer in tubers and caused disease better than a tropical strain. These data indicate interaction with plants is required for the temperate epidemiological trait of R3bv2.