Bacteria of genus Methylobacterium have been found to promote plant growth and regulate the level of
ethylene in crop plants. This work is aimed to test the induction of defense responses in tomato against
bacterial wilt by stress ethylene level reduction mediated by the ACC deaminase activity of Methylobacterium
strains. Under greenhouse conditions, the disease index value in Methylobacterium sp.
inoculated tomato plants was lower than control plants. Plants treated with Methylobacterium sp.
challenge inoculated with Ralstonia solanacearum (RS) showed significantly reduced disease symptoms
and lowered ethylene emission under greenhouse condition. The ACC and ACO (1-aminocyclopropane-1-
carboxylate oxidase) accumulation in tomato leaves were significantly reduced with Methylobacterium
strains inoculation. While ACC oxidase gene expression was found higher in plants treated with R. solanacearum
than Methylobacterium sp. treatment, PR proteins related to induced systemic resistance like
b-1,3-glucanase, PAL, PO and PPO were increased in Methylobacterium sp. inoculated plants. A significant
increase in b-1,3-glucanase and PAL gene expression was found in all the Methylobacterium spp. treatments
compared to the R. solanacearum treatment. This study confirms the activity of Methylobacterium
sp. in increasing the defense enzymes by modulating the ethylene biosynthesis pathway and suggests
the use of methylotrophic bacteria as potential biocontrol agents in tomato cultivation.