| he pathogenesis and phylogeny of Pseudomonas syringae pv. syringae (Pss), the cause of basal kernel blight of barley, and its bioiogical control by antagonistic Pantoea agglomerans Pa, (syn. Erwinia herbicola, Eh) was investigated. Scanning electron micrographs located bacteria close to stomata and bases of kernel trichomes. Light micrographs revealed Pss in intercellular spaces of aleurone and amyloplast cells. Electron micrographs demonstrated Pss in xylem vessels and cell wall degradation in association with capsule protected bacteria.;Fifty-five Pss strains, isolated from infected kernels of 12 barley cultivars were tested for tobacco hypersensitivity, pathogenicity, toxin production and carbon source utilization. Toxin production correlated low (r = 0.31; p = 0.046) with pathogenicity, but 96% of toxin-plus strains were pathogenic, supporting the importance of toxins for virulence. Nutritional analyses revealed a phenotypic variability of Pss strains with similarity coefficients between 76-100%. The intrapathovar variation of Pss populations was analyzed by RFLPs of digested DNA using XbaI, SpeI and pulsed field gel electrophoresis. Macrorestriction fingerprinting supported a heterogeneity of Pss populations (43-77% similarity).;Field experiments (1994, 1995) revealed 45-70% disease control, when Pa was applied to batley heads prior to the Pss infection window. Pa provided 80-100% disease reduction in greenhouse studies. Efficacy of Pa was affected by time and rate of application, with a single application providing control. Survival of formulated Pa was better when stored at 4 C than 22 C. Biocontrol activity was not affected by storage.;Multiple mechanisms including antibiosis, preemptive exclusion, and induced systemic resistance were involved in the Pa-Pss interaction. Antibiotics were polar, thermostable, protease insensitive, but base labile (pH... |
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