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 populatio n sizes of Xanthomonas translucens pv. translucens strain Xtt4Rif-2 and bac terial 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 wh eat 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 inocula tion of the pathogen and disease severity was assessed 5-6 days later. Thir teen bacterial epiphytes were identified by their ability to reduce Xtt4Rif -2 populations, disease severity, or both compared to a pathogen-only contr ol (subsequently referred to as successful antagonists). The potential role s of antibiosis and competition for nutrient resources in mediating the obs erved interactions between the epiphytes and the pathogen were also investi gated. Only one epiphyte inhibited Xtt in vitro. Thus, antibiosis probably was not a major mechanism by which pathogen population sizes and disease se verity were reduced. Similarity in nutrient utilization between bacterial e piphytes and pathogen strain Xtt4Rif-2 was estimated using nutrient-overlap indices. Nutrient-overlap indices were not predictive of the ability of ep iphytes to reduce pathogen populations or disease severity. However, succes sful antagonists utilized both sucrose and inositol more frequently than po or antagonists. (C) 2000 Academic Press.