Interactions between Xanthomonas translucens pv. translucens, the causal agent of bacterial leaf streak of wheat, and bacterial epiphytes in the wheat phyllosphere

The abilities of 44 bacterial epiphytes to reduce leaf-associated population sizes of Xanthomonas translucens pv. translucens strain Xtt4Rif-2 and bacterial leaf streak were quantified in growth-chamber experiments. Bacterial epiphytes were inoculated individually onto 10-day-old wheat seedlings at a density of 10(8) CFU/ml. Pathogen strain Xtt4Rif-2 was inoculated onto wheat seedlings 48 h later at a density of 10(7) CFU/ml. Population sizes of the bacterial epiphytes and the pathogen were quantified 48 h after inoculation of the pathogen and disease severity was assessed 5-6 days later. Thirteen bacterial epiphytes were identified by their ability to reduce Xtt4Rif-2 populations, disease severity, or both compared to a pathogen-only control (subsequently referred to as successful antagonists). The potential roles of antibiosis and competition for nutrient resources in mediating the observed interactions between the epiphytes and the pathogen were also investigated. Only one epiphyte inhibited Xtt in vitro. Thus, antibiosis probably was not a major mechanism by which pathogen population sizes and disease severity were reduced. Similarity in nutrient utilization between bacterial epiphytes and pathogen strain Xtt4Rif-2 was estimated using nutrient-overlap indices. Nutrient-overlap indices were not predictive of the ability of epiphytes to reduce pathogen populations or disease severity. However, successful antagonists utilized both sucrose and inositol more frequently than poor antagonists. (C) 2000 Academic Press.