Bacterial wilt-resistant tomato rootstock suppresses migration of ralstonia solanacearum into soil

Ralstonia solanacearum, the causal agent of bacterial wilt of tomato, grows in infected plants and migrates from the roots into the soil. We investigated the effectiveness of bacterial wilt-resistant tomato rootstock in reducing the migration of R. solanacearum from susceptible scions into the soil. Rootstock stems were either 3–5 cm tall (low-grafted, LG) or ≥ 10 cm tall (high-grafted, HG). After inoculation of scions of the susceptible cultivar (SC) with R. solanacearum below the first flower, there was no difference in disease progression among LG, HG, and ungrafted SC plants, and plants had wilted by 2 weeks. However, the rate of detection of R. solanacearum in the soil of wilted plants was reduced by grafting. The size of the R. solanacearum population in the soil of fully wilted plants increased in the order of HG < LG < SC. These results show that grafting onto resistant rootstock strongly suppressed the migration of R. solanacearum into the soil by the time of full wilting, and the effect was stronger with a longer rootstock. Migration of R. solanacearum into soil increased with increasing disease severity in SC, LG and HG. These facts suggest that early uprooting of slightly infected plants could control the spread of the bacteria into the soil.