Phylotype II race 3 biovar 2 strain of Ralstonia solanacearum in Taiwan: survival potential and virulence on tomato, eggplant, and pepper
2015
Phylotype II race 3 biovar 2 (R3b2) strains of Ralstonia solanacearum are mostly present in temperate regions and tropical highland areas. The strain was first identified in Taiwan in 1999 in the central western lowlands. A severe epidemic of potato brown rot occurred in 2006 in Yunlin, Taiwan. Since then, the disease has occurred sporadically in this area. During the crop season of 2011 the pathogen was monitored on weeds in potato fields with a history of brown rot in Yunlin. The positive detection rate was only 1.7% among the 120 samples of six weed species. The pathogen was detected from roots of Amaranthus viridis and Portulaca oleracea present in one field with plants exhibiting disease symptoms. The effect of weeds (with or without weeding) and soil microbial populations (with or without steam sterilization) on the survival of R3b2 strain Pss525 was examined in a greenhouse trial without the presence of the host crop. Results showed Pss525 survived the longest (at least 245 days) in steam-sterilized soils. In non-sterilized soils, the survival time decreased to 175 and 105 days with and without the presence of weeds, respectively. The virulence of 45 R3b2 potato strains was evaluated on resistant (‘Hawaii7996’, ‘EG203’, ‘PBC066’) and susceptible (‘L390’, ‘EG048’, ‘PBC1367’) cultivars of tomato, eggplant, and pepper. Overall, the potato strains showed greater virulence on tomato and eggplant, and the virulence was greater in summer (mean temperature: 25 to 30°C) than in winter (mean temperature: 14 to 22°C). A larger variation in virulence was observed on tomato and eggplant during the winter season. Most strains showed greater virulence on ‘EG203’ in winter. Our results suggest R3b2 could be a potential threat for winter tomato and eggplant production in Taiwan, if the pathogen becomes established in tropical lowlands.
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