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Temperature adaptation of Ralstonia solanacearum strains correlates with disease incidence.
A. I. HUERTA (1), A. Milling (1), C. Allen (1). (1) University of Wisconsin, Madison, WI, U.S.A.

Bacterial wilt, caused by members of the <i>Ralstonia solanacearum</i> species complex, is an economically important vascular disease affecting many crops. Strains of this heterogenous group of soilborne bacteria have adapted to diverse environments by unknown mechanisms. Human activity has disseminated <i>R. solanacearum</i> strains, increasing their global agricultural impact, but intermingling of strains has not been observed in the field. We hypothesized that tropical strains enjoy a competitive advantage over temperate ones in tropical environments and that temperate strains can outcompete tropical strains in temperate conditions. <i>R. solanacearum</i> strains GMI1000 (tropical), UW551 (temperate Race 3 biovar 2) and K60 (U.S. warm-temperate) are phylogenetically distant but can all wilt tomato. While GMI1000 does not survive in the cooler regions where UW551 originated and causes disease, UW551 and K60 can cause disease at both temperate (24°C day/19° night) and tropical (28°) temperatures in a controlled environment. In 1:1 competition assays on tomato plants, subtropical strain K60 was significantly more competitive than GMI1000 and UW551 in tomato rhizospheres and stems at 28°C. Tropical strain GMI1000 also outcompeted UW551 at 28°C. As expected, at 24°/19°C, temperate strain UW551 outcompeted both GMI1000 and K60 in the rhizosphere, but showed no competitive advantage over GMI1000 in stems, whereas K60 did. K60's high competitive ability <i>in planta</i> may result from its production of a diffusible factor that inhibited growth of GMI1000 and UW551 on agar plates. These results suggest that temperature adaptation could explain why R3bv2 strains rarely cause disease in tropical lowlands.<p><p>Keywords: Bacteria-Phytoplasma-Spiroplasma-Fastidious Prokaryote, Vegetables, Tomato

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