The Effect of Rhizosphere Bacterial Consortium on the Manifestation of Tobamoviral Infection Symptoms on Tomato

Abstract

Contrary to available reports on the prevalence of microbial diseases of tomato in Nigeria, the emergence of mosaic viral disease on tomato farms is gradually becoming a very significant additional threat to the production of this economically important vegetable crop. In addition, the resistance of Tobamoviral diseases to chemical control measures makes them particularly difficult to control, once established. Unlocking the specificity of rhizosphere microbiome towards the general health and performance of tomato is key to achieving a safer means of combating microbial diseases of tomato. In this study, the predominant rhizosphere bacteria associated with healthy and infected tomato were compared, and the effect of tomato seed treatment (with selected rhizobacterial consortium) on the incidence of Tobamoviral infection symptoms was determined. Bacillus thuringiensis, Pseudomonas aeruginosa, Bacillus subtilis, Bacillus macerans and Bacillus cereus were isolated from the rhizosphere of healthy tomato plants using the pour plate isolation method, while P. aeruginosa and B. subtilis were not isolated from rhizosphere samples associated with infected tomato. Tomato seeds were treated with the predominant rhizobacterial consortium isolated from healthy tomato plants, while seedlings were mechanically inoculated with triturated tissue extracts from infected plants. Significant reduction in the incidence of Tobamoviral disease symptoms were recorded on tomato plants grown from treated seeds. Additional (new) Tobamoviral disease symptoms were not recorded at the second, fifth and sixth weeks after the transmission of the pathogen in treated plants while disease incidence values of 23.83, 3.03 and 3.33% were recorded on untreated plant set respectively. Average growth performance measures, including the fruit count, fruit weight, stem girth and the number of flower clusters per plant at 16.76, 43.80 g, 0.93 cm and 9.67 respectively were significantly higher in treated tomato plants than in plants grown without the seed treatment. Consequently, it could be inferred that the healthy-tomato associated rhizosphere bacterial consortium used in this study influenced the resistance of mechanically inoculated tomato to the manifestation of Tobamoviral infection symptoms and the overall performance of the plant.