Fusarium wilt disease caused by Fusarium oxysporum f.sp. lycopersici (FOL)
is a significant disease of tomatoes in Thailand. It can reduce the yield of tomatoes up
to 50-80%. Plant Growth Promoting Rhizobacteria (PGPR) can promote plant growth
either directly by the improvement of physiological metabolic processes or indirectly
by the suppression of various plant diseases. Apart from the PGPR, many other elicitors
such as chitosan is a natural biopolymer derived from deacetylation N-acetyl-Dglucosamine
sugar of chitin. The objective of this study was to evaluate of Bacillusbased
chitosan formulations (BBC) for the control of pathogen fungus FOL on
tomatoes. Chitosan formulation as BBC1, BBC2, and BBC3 at different concentration
of 800, 1000, 1200 and 2000 μg/ml were tested by dual culture technique. The results
showed that BBC1 at a concentration of 800 μg/ml had the most effective inhibited
mycelial growth of FOL at 45.14%, significantly higher than positive control (Terraclor
Super-X). When applied as foliar treatment together with soil drenching and inoculated
with the fungus at 7 days, BBC1 at a concentration 800 μg/ml showed the reduction of
fusarium wilt disease at 78.95%, statistically significant compared to distilled water.
Moreover, the results of environmental scanning electron microscope (ESEM) analysis
showed that the mode of action of BBC1 at a concentration 800 μg/ml could be direct
inhibition to growth of FOL by secreting antifungal compounds. These results indicated
that the formulation of biocontrol agents as BBC can be applied to control or inhibit the
growth of the fusarium wilt pathogen of tomatoes.