Biocontrol of Alternaria brassicicola on cabbage seedlings and Glomerella cingulata on strawberry seedlings by endophytic Streptomyces spp.

Abstract: Endophytic Streptomyces sp. strain MBCN152-1 which was isolated from cabbagegreatly reduced disease severity on plug-seedlings of cabbage after spray-inoculation withAlternaria brassicicola. Furthermore, amendment of growing medium with MBCN152-1strongly inhibited the incidence of damping-off of cabbage seedlings raised from seedsartificially infested with A. brassicicola. Microscopic observation revealed that hyperparasitismis one of the modes of action of strain MBCN152-1. These results indicated that strainMBCN152-1 is a suitable candidate for the biological control of A. brassicicola. Endophyticactinomycetes, isolated from strawberry plants, were tested for inhibition of anthracnose, causedby Glomerella cingulata, on detached leaflets and plug seedlings of strawberry. Streptomyces sp.strain MBFA-172 strongly inhibited symptom development on the detached leaflets andsignificantly reduced disease incidence on strawberry plug seedlings. Strain MBFA-172 providedhigher level of protection than a commercial biofungicide (Talaromyces flavus) and comparablelevel with a chemical fungicide (propineb) under greenhouse conditions. A spontaneousthiostrepton-resistant mutant of MBFA-172 colonized aboveground parts of strawberry plants atmean population densities of 3.2 × 103 to 7.2 × 105 cfu/g (fresh weight) even after 21 days offoliar application. These results indicated that MBFA-172 has a great potential as a biocontrolagent for strawberry anthracnose.