Biological control of Fusarium wilt on tomatoes
use of Bacillus subtilis and interactions with the earthworm Pontoscolex corethrurus in a Kenyan highland soil
BiocontrolBCABacillus subtilisFusarium wiltFusarium oxysporumEarthwormsPontoscolex corethrurusTomatoesKenyaTropical highland soil
It is important to investigate the potential of biological control measures in agricul-ture, especially where economic issues restrict the use of expensive inputs or when there are environmental concerns about toxicity of agrochemicals. The bacterium Bacillus subtilis has proved promising as a biocontrol agent (BCA) in suppressing various plant diseases and it has also been shown to promote plant growth in certain cases. During this study, the effect of B. subtilis on Fusarium wilt (caused by the fungus Fusarium oxysporum) on tomatoes, as well as its effect on the earthworm species Pontoscolex corethrurus was investigated. Furthermore, the combined ef-fect of the BCA with P. corethrurus on tomatoes and F. oxysporum was investigat-ed. This was done in three different experiments: 1) Laboratory study evaluating the effect on germination and growth of tomato seeds treated with B. subtilis received from University of Nairobi alternatively isolated root bacteria and infected with F. oxysporum, 2) Greenhouse experiment testing the effect alone and in combination of B. subtilis and P. corethrurus on F. oxysporum and tomato plants, 3) Toxicity experiment of B. subtilis on P. corethrurus. The results showed a positive effect of B. subtilis on plant dry biomass but did not increase the plant height. In addition, it showed tendencies of suppressing the disease caused by F. oxysporum, though, the results were not significant. However, the results were inconsistent and more re-search and experiments should be performed, evaluating the effect using different volumes and concentrations of the BCA. Furthermore, B. subtilis did not have a negative effect on P. corethrurus in this study. Since certain strains of B. subtilis have potential of working as BCAs, and are a promising and potentially environ-mentally friendly plant disease control bacteria, it is interesting to continue per-forming research on different crops and in different settings, as well as in combina-tion with other BCAs. It is desired to develop a plant protection method that is easily available and applicable in all parts of the world, but with emphasis on small-scale farmers with limited means to access expensive chemical inputs.