Department of Plant Pathology, University of Hawaii at Manoa, Honolulu 96822-2279
Effects of single versus multiple biological control agents (BCAs) on suppression of bacterial blight of anthurium were studied using a bioluminescent strain (V108LRUH1) of Xanthomonas campestris pv. dieffenbachiae. When five BCAs (GUT3, GUT4, GUT5, GUT6, and GUT9) were coinoculated in various combinations with V108LRUH1 into filter-sterilized guttation fluids of anthurium plants, a mixture of all five strains or four strains without GUT9 was most inhibitory to V108LRUH1. None of the individual BCAs inhibited V108LRUH1 in the guttation fluid. When BCAs were sprayed at ≅108 CFU/ml on the foliage of a susceptible cultivar 1 day prior to inoculation with V108LRUH1, GUT6 alone and any mixtures containing GUT6 were highly effective in suppressing wound invasion and subsequent leaf infection by V108LRUH1. When tested on several cultivars that differed in susceptibility to the disease, the mixture of five strains or four strains without GUT9 consistently suppressed leaf infection regardless of the cultivars. In some cultivars, BCAs completely suppressed both wound and hydathode invasion by V108LRUH1, resulting in no infection in many leaves. These results indicate that application of bacterial mixtures provides anthurium cultivars with bacterial communities suppressive to X. campestris pv. dieffenbachiae. The results also suggest that selecting an effective mixture of BCAs first and then removing ineffective strains may be a better general approach to finding the most effective BCAs than finding individual strains and combining them.