Characterization and management of bacterial wiltcausing pathogen(s) of tomato in Tanzania

Abstract

Bacterial wilt disease (BWD), caused by Ralstonia solanacearum (Smith) is one of the most destructive tomato diseases globally. A research was carried out from 2017 to 2019 to assess the incidence and severity of tomato BWD, characterize the pathogen and evaluate effects of selected pesticidal plants against BWD. Results indicated that 55.17% of the surveyed fields in different districts in Tanzania were significantly (p ≤ 0.05) infected by BWD with overall disease incidences and severities ranging from 5.8 to 44.6% and 10.70 to 59.30% respectively. Majority (70%) of farmers used synthetic chemicals, 13% used botanical, 10% did crop rotation and 7% did not use any BWD management measure. A total of 29 Ralstonia isolates were isolated from infected tomato plants out of which 19 (52%) were pathogenic on tomato variety Tanya. Carbohydrate oxidation test showed that most (90%) predominating isolates in the main agro-ecological zones belong to biovar 3 while the rest (10%) belong to biovar 2 and prevail in the southern zone of Tanzania. This is the first report of prevalence of biovar 2 of Ralstonia in Tanzania and it alerts global plant health regulators to prevent new introduction and/or spread of Ralstonia. Phylogenetic analysis based sequence data generated from the 16S-23S internal transcribed spacer (ITS) of isolates revealed that most (80%) were phylotype I and III and the rest (20%) were phylotype II of R. pseudosolanacearum and R. solanacearum geno-species respectively. Such results implied that BWD in the country is caused by diverse Ralstonia populations. In screening the effect of 20 plant extracts, the findings revealed that R. solanacearum can be managed using extracts from one of the tested plants (Patent Application ID Number G190916-2061) which was as effective as the positive control (ampiclox) in inhibiting growth of Ralstonia in in-vitro conditions. It produced inhibition zone of 19.25 mm almost similar to 20.58 mm by the ampiclox compared with 0.00 mm of the negative control. Similarly, the application of the extracts of the most effective plant managed BWD severity on tomato seedlings grown in screen-house 100% compared with the untreated seedlings which wilted. Therefore the extract from the most effective plant will be recommended after patenting for developing effective and sustainable management strategies of BWD in Tanzania based on the pathogen characteristics as generated during this study.