Potential of Host Resistance and Efficient Water Use in Management of Bacterial Wilt of Tomatoes in Kajiado County

Abstract

Tomato (Solanum lycopersicum) is an important vegetable consumed for its nutritional value in Kenya and around the world. Bacterial wilt disease caused by Ralstonia solanacearum is a major production constraint in tomato that cause an estimated yield loss of 35% to 90% in the field and greenhouse. Current management methods used to manage bacterial wilt are inadequate and they pose safety risks to the environment and human health. The objectives of this study were (i) To determine the reaction of common tomato varieties to infection by bacterial wilt disease, (ii) To assess the effect of watering regimes on bacterial wilt on selected tomato varieties in the greenhouse and (iii) To determine the effect of different irrigation systems on incidence and severity of selected tomato varieties infected with bacterial wilt disease. Greenhouse and field experiments were carried out at Kabete Field Station University of Nairobi and at Isinya in Kajiado County-Kenya respectively in the year 2021 and 2022. For the first objective, eighteen tomato varieties were screened against R. solanacearum and the experiment was laid out in a randomized complete block design (RCBD) with 3 replications. In the second objective, the experiment was laid out in a completely randomized design (CRD) with three varieties namely Big rock F1, Assila F1 and Riogrande subjected to three moisture levels: 50% field capacity (FC), 100%FC and 120%FC. For the third objective, field experiments on drip and furrow irrigation systems were laid out in a RCBD with 4 replications. For the greenhouse experiments plants were inoculated with Ralstonia solanacearum at a concentration of 1× 108 cfu/ml two weeks after transplanting while disease assessment was done eight days after inoculation. Bacterial wilt incidence, severity, stem browning, growth and yield parameters were assessed. Data collected was subjected to analysis of variance and means separated by Protected Fishers Least significance difference at 5% probability. Incidence and severity of bacterial wilt were highly significantly different (P<0.001) among the varieties screened. Non-hybrid varieties Riogrande, Isisementi and Rionix were highly susceptible to bacterial wilt with high incidence and severity scores of disease index (DI) 0.61-0.9. Kilele F1 variety had the lowest incidence and severity score of bacterial wilt and was found to be highly resistant to bacterial wilt with DI of 0.18. Terminator F1, Big rock F1 and Bravo F1 were resistant with a DI of 0.21 - 0.3. Inoculation of R. solanacearum to the eighteen varieties had significant effect on stem browning and growth parameters compared to the non-inoculated varieties. Big rock F1, Assila F1and Riogrande F1 had lowest severity scores of 0.83, 1.77, and 2.26 and lowest incidences of 35.4%, 58.3% and 77.1% at 50% field capacity (FC) respectively. At 100%FC, severity score and incidence were lowest in Big rock F1 with 1.04 and 41.7% and highest in Riogrande with 2.94 and 85.4% respectively. Highest incidence was recorded at 120% FC from Riogrande variety with 91.7%. On field experiments, lowest incidences were recorded in Big rock F1 and Big rock F1 with Chemical treatment (Brono pol) with 17.3% and 17.2% under drip and furrow irrigation systems respectively. Highest incidence was recorded on Riogrande variety with 44.5% in furrow irrigation and Riogrande with Chemical treatment with 38.8% under drip irrigation. Highest yields were obtained in drip irrigation on Big rock with chemical treatment with 78.2t/ha on drip irrigation and 39.6t/ha on furrow irrigation while lowest yields were obtained from Riogrande variety with 44.3t/ha under drip irrigation and 16.2t/ha under furrow irrigation. The results showed that bacterial wilt disease is highly influenced by moisture levels in the soil. The type of irrigation system also influences the multiplication and spread of R. solanacearum in the soil. The findings showed that resistant cultivars had great positive impact in management of R. solanacearum. Therefore, the combination of resistant varieties with appropriate moisture under a suitable watering regime like drip can be incorporated in integrated disease management programs to manage bacterial wilt disease on infected fields.