Effect of grafting on yield of commercial tomato cultivars grown under bacterial wilt (Ralstonia solanacearum) infested soil

Introduction - Grafting is a chemical -free intervention and an environmentally friendly method for controlling soil -borne diseases and abiotic stresses such as flooding. Tomato grafting is a well-known practice for bacterial wilt management, but constrained by the presence of multiple strains of its causal agent Ralstonia solanacearum. The effect of grafting on susceptible tomato cultivars grown under phylotype I, sequevar 1-31 strain infested soil was assessed to help tomato producers in the long term. Materials and methods - Tomato cultivars Anna F1' and 'Tanya' (susceptible) and 'Tengeru 97' (resistant) were grafted on a resistant rootstock line Hawaii 7996 and evaluated under infested greenhouse soil in Arusha, Tanzania in 2016 and 2017. Wilt score, yield, and other horticultural traits were collected from a randomized complete block design experiment with three replications. Results and discussion - Grafting delayed flowering, and slowed down plant growth at the initial growth stage as observed from plant height measured at flowering. Grafted 'Anna F1' and 'Tanya' gave significantly higher marketable fruit numbers, size and yields than the corresponding un-grafted controls. Percent wilted plants reached 100, 98 and 12% in un-grafted 'Anna F1', 'Tanya' and 'Tengeru 97', respectively, against 13, 15 and 18% in grafted combination with 'Hawaii 7996', respectively. Advantage of grafting was evident in 'Anna F1' and 'Tanya', but not in 'Tengeru 97'. Conclusion - Grafting could play a significant role to exploit the potential of bacterial wilt susceptible cultivars that otherwise have desirable traits. Identifying genes controlling resistance in 'Tengeru 97', characterizing the various strains, and search for new sources of resistance are sought. In parallel, farmers' training in bacterial wilt management to suppress the inoculum load and increase the longevity of 'Tengeru 97' remains essential.