development of an efficient screening system for resistance of tomato cultivars to ralstonia solanacearum

This study was conducted to establish an efficient screening system for resistant tomato to bacterial wilt caused by Ralstonia solanacearum. Under several conditions such as inoculation methods, growth stages of tomato seedlings, inoculum concentrations, and incubating temperatures after inoculation, development of bacterial wilt on nine resistant or susceptible cultivars of tomato was investigated. To inoculate by drenching the non-cut roots with the bacterial suspension was better to distinguish resistance and susceptibility of tomato cultivars than by drenching the cut roots using scalpel. And ‘Hawaii7996’ a resistant tomato to R. solanacearum showed high resistance at all the tested conditions including growth stages (3-, 6-, 8-, 10-leaf stages), inoculum concentrations (OD600=0.1-0.4) and incubation temperatures (25, 30, 35°C). On the other hands, susceptible cultivars represented disease index of 3.7 and 3.9 at 6- and 8-leaf stages, respectively. At 3- and 10-leaf stages, the cultivars demonstrated lower disease severity of 2.1 and 0.5, respectively, than at 6- and 8-leaf stages. When the inoculated seedlings were incubated in growth chambers of 25, 30 and 35°C, disease severity of susceptible cultivars was significantly greater at 30 and 35°C than at 25°C. In addition, the level of resistance of the tomato cultivars was not significantly affected by inoculum concentrations of OD600=0.1–0.4. On the basis of the results, we suggest an efficient screening method to measure resistance level of tomato cultivars to bacterial wilt. The eight-leaf stage seedlings transplanted 7 days before inoculation, are inoculated with R. solanacearum by drenching the non-cut roots with a bacterial suspensions (OD600=0.4) to give inoculum volume of 50 ml/soil l. The inoculated plants are incubated in a growth room at 30°C for 12-13 days with 12-hour light a day.