Antagonistic activity of Pseudomonas aeruginosa from compost against Pythium aphanidermatum and Fusarium solani

This study was conducted to investigate the presence of native antagonistic bacteria from compost and to evaluate their ability to suppress Pythium and Fusarium-induced damping-off of cucumber. Seven bacterial strains isolated from compost were screened for their in vitro antagonism against Pythium aphanidermatum and Fusarium solani. Out of these, two strains designated as ISO1 and ISO2 showed significant level of antagonism. Scanning electron microscopic observation of the mycelium of P. aphanidermatum and F. solani at the inhibition zones showed morphological changes in the hyphae including deformation, shrinkage and loss of turgidity. Based on 16S rDNA gene sequence analysis, both bacterial strains (ISO1 and ISO2) were identified as Pseudomonas aeruginosa. The cell-free culture filtrates of P. aeruginosa ISO1 and ISO2 significantly reduced the mycelial growth of P. aphanidermatum and F. solani under in vitro conditions. Compatibility analysis of the bacterial strains using cross-streak assay showed that they are compatible to each other. In addition, both strains were found effective in controlling P. aphanidermatum-induced damping-off of cucumber. Soil application of P. aeruginosa ISO1 and ISO2 reduced the yellowing and stunting of cucumber seedlings caused by F. solani. This study demonstrates the effectiveness of P. aeruginosa strains ISO1 and ISO2 isolated from compost in the management of damping-off of cucumber. It also shows that compost can harbour bacterial strains with antagonistic activity against P. aphanidermatum and F. solani.