Comparisons of single versus multiple bacterial species on biological control of anthurium blight

Effects of single versus multiple biological control agents (BCAs) on suppr ession 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 combi nations with V108LRUH1 into filter-sterilized guttation fluids of anthurium plants, a mixture of all five strains or four strains without GUT9 was mos t inhibitory to V108LRUH1. None of the individual BCAs inhibited V108LRUH1 in the guttation fluid. When BCAs were sprayed at congruent to 10(8) CFU/ml on the foliage of a susceptible cultivar 1 day prior to inoculation with V 108LRUH1, 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 dis ease, 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 appli cation of bacterial mixtures provides anthurium cultivars with bacterial co mmunities suppressive to X. campestris pv. dieffenbachiae. The results also suggest that selecting an effective mixture of BCAs first and then removin g ineffective strains may be a better general approach to finding the most effective BCAs than finding individual strains and combining them.