In-Vitro Antagonistic Effect of Bacillus thuringiensis on Ralstonia solanacearum, the Causal Agent of Bacterial Wilt Disease of Tomato (Lycopersicon esculentum Mill).

Abstract

Tomato (Lycopersicon esculentum, Mill) is a rich source of vitamins, minerals and lycopene, which has many health benefits. However, its production is hampered by bacterial wilt caused by Ralstonia solanacearum resulting in significant yield losses. Use of chemicals in the control of plant pathogens has detrimental effects on humans and the environment in terms of leaving residues in soil which later find their way into underground waters. Therefore, it is desirable to find an alternative to chemical control of this bacterial pathogen. This study investigates the potential of native Bacillus thuringiensis (Bt) for biological control of Ralstonia solanacearum (Rs) under laboratory conditions. B. thuringiensis was isolated from cultivated soil, non- cultivated soil, stagnant water, sawdust, horse dung, grain dust, dead leaves and poultry manure. R. solanacearum was isolated from stem exudates of bacterial wilt infected plants and its pathogenicity assay was carried out using 2-week-old seedlings of Beske tomato variety. The Bt and R. solanacearum isolates were then characterized phenotypically. Bt isolates were further identified using endospore and parasporal staining techniques. All the Bt isolates were tested for in-vitro antagonistic activity on R. solanacearum using agar well diffusion method. Isolates Bt2, Bt16, Bt17, Bt32 and Bt34 were confirmed as Bacillus thuringiensis while isolate Rs was confirmed as R. solanacearum. Beske showed wilting symptoms from the fourth day of inoculation and eventual death of seedlings. The zone of inhibition exhibited ranged from 0.0 mm to 20.0 mm.

Keywords: Bacillus thuringiensis, In-vitro, Bacterial wilt, Ralstonia solanacearum, Tomato