Evaluation of local Solanum torvum as a rootstock to control Ralstonia solanacearum in Indonesia

Bacterial wilt of tomato and eggplant caused by Ralstonia solanacearum is difficult to control due to variability of the pathogen and lack of durable resistance in host plants. Solanum torvum has been reported to be resistant against bacterial wilt caused by R. solanacearum and has been used as a rootstock in some countries. Several native plants were collected around Yogyakarta area and its vicinity and tested for their susceptibility against bacterial wilt by artificial inoculation. All plants exhibited high resistance against R. solanacearum. Local commercial cultivars of tomato (‘Sanmarino’) and eggplant (‘Kalenda’) were cleft grafted onto Solanum torvum then inoculated with a highly virulent strain of race 1 biovar 3. The development of bacterial wilt was observed every week and population dynamics of R. solanacearum in the root, collar, stem (scion), and stem (rootstock) was determined at 10, 20, and 30 days after inoculation. All grafted plants as well as S. torvum did not exhibit wilt symptoms until one month after inoculation. On the contrary, ungrafted eggplant ‘Kalenda’ wilted within the first week after inoculation (disease index 29) and at 30 days after inoculation the disease index reached 96.4. The ungrafted tomato ‘Sanmarino’ had severe wilt by the first week after inoculation (disease index 51.2) and completely wilted at 30 days after inoculation. Although all grafted plants showed no wilt symptom, the plants were lately infected with the pathogen but at lower populations compared with those in the scion controls. The colonization of the pathogen in root and collar regions after inoculation is common in resistant and susceptible cultivars. The degree of bacterial colonization in the upper stem was an important factor that determined the resistant and susceptibility of eggplant and tomato to bacterial wilt. Resistance of grafted plants to bacterial wilt was determined by rootstock.