Evaluation of grafting technology for management of bacterial wilt (Ralstonia solanacearum) of tomato (Solanum lycopersicum L)
Kanyua, S. Ignatius
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Tomato (Solanum Lycopersicun L) is a very important vegetable grown mainly by small scale farmers in most arable areas in Kenya. Tomato production has declined drastically due to attack by Ralstonia solanacearum, a soil borne pathogen which causes bacterial wilt. Transmission of pathogen occurs when bacterial ooze from the plant enters the surrounding water or soil, contaminates farming equipment or by insect vectors. The disease has not yet been effectively managed. Grafting is an asexual plant propagation technique that involves joining the scion of desirable cultivar onto a resistant rootstock of another compatible species. The overall objective of the study was to investigate the potential use of grafting technique for the management of bacterial wilt in tomato. A survey was first conducted in Kirinyaga County to determine the important pests, pathogens, tomato varieties grown and other key tomato production constraints. Secondly, rootstocks comprising varieties from the Solanaceae family namely Solanum melongena, Capsicum annum L., Solanum incarnum and the bacterial wilt resistant tomato cultivar (Mt56) were evaluated. A tomato cultivar well adapted to greenhouse environment (Anna F1) and one grown under field conditions (Cal J) were used as the scion material. Bacterial inoculum isolation was done using CPG Medium and TZC was used to identify distinct colonies of R. solanacearum. Pathogen inoculum was introduced to the test plants and disease severity data recorded using 0 to 5 scoring scale. Growth vigor of the inoculated and uninoculated seedlings and number of days to wilting were recorded. Data were subjected to ANOVA using Genstat version 15 and significantly different treatment means separated using LSD at P < 0.05. Solanum melongena, Solanum incarnum and bacterial wilt resistant tomato cultivar (Mt56) did not develop infection and were used as rootstocks for grafting to susceptible scions to check for compatibility and confirm effectiveness. The Capsicum annuum had a 5 scale disease severity and was not further studied. From the survey results, the highest proportion by gender engaged in tomato production is male. The greatest challenge affecting tomato production in Mwea East locations was bacterial wilt. Grafting was done when seedlings were at 2-3 leaf stage and cleft grafting method was used. The rootstocks and scions were compatible on Mt56 + Anna F1 (93.30% take), Mt56 + Cal J (76.7% take), S. melongena + Anna F1 (96.7% take), S. melongena + Cal J (83.3% take), S. incarnum + Anna F1 (73.3% take), and S. incarnum + Cal J (100% take). Grafted plants had higher survival percentage and reduced disease severity as compared to the ungrafted susceptible Cal J. From the study, it was concluded that farmers have limited information on bacterial wilt and use less effective management strategies. Additionally, resistant germplasm to bacterial wilt exists and can be successfully utilized to graft susceptible tomato cultivars and contribute to management of bacterial wilt at 2-3 leaf stage. It is recommended that, further studies on other solanaceous varieties with potential for use in tomato grafting should be conducted, need for cost benefit analysis of the tomato grafting technology and more research and experimental work to test resistant varieties which do not require grafting to be conducted.