Novel and rapid agar plate methods for in vitro assessment of bacterial biocontrol isolates’ antagonism against multiple fungal phytopathogens

Biological control of plant diseases with antagonistic bacteria is a promising alternative to conventional chemical control strategies. In vitro screening for inhibition of mycelial growth of phytopathogenic fungi by bacterial isolates is the first step in selecting putative bacterial biocontrol agents. Dual culture plate assay is the most common method involved in this first-line selection process. However, it needs independent agar plates to test antagonism by a specific bacterial isolate against each of the fungal phytopathogen. Two modified in vitro antagonism tests are proposed here. Antagonistic activity of a putative biocontrol bacterial strain against four different fungal phytopathogens could be assessed in a single agar plate simultaneously. A comparison of the new methods with conventional dual culture plate assay was also done. The proposed methods are easy to perform and results of antagonism are obtained rapidly. Results of fungal inhibition were qualitatively comparable with that generated through dual culture plate assay. Quantity of resources such as agar medium and plates required for the modified antagonistic assays is several folds less than that required for dual culture plate assay.