First report of bacterial blight caused by Acidovorax avenae subsp. avenae associated with finger millet seeds from Uganda

Finger millet (Eleusine coracana (L.) Gaertn.) is an important food crop for Uganda. Information on bacterial diseases of this crop in Uganda is limited. Ekwamu (1980) reported bacterial blight caused by Xanthomonas axonopodis pv. coracanae (Desai et al.) Vauterin et al. Seedlings of finger millet grown in soil under controlled conditions (30°C, 12 h light/ dark cycles) showed severe blight and necrotic stripe symptoms similar to those incited by Acidovorax avenae subsp. avenae. Seeds were further tested for this bacterium by a seedling symptom test (Shakya and Chung, 1983). Nine out of ten seed samples collected from eastern, central, and western regions of Uganda showed 25-35% of seeds to be infected. Bacterial ooze was observed under the compound microscope from sections of leaves showing blight and stripe symptoms. A bacterium was isolated when leaf macerate was streaked on to nutrient agar or King's medium B agar plates and incubated at 28±2°C. Translucent, whitish-grey bacterial colonies measuring 2-3 mm and having fringed margins appeared after 24 h. The strains were identified by ELISA using antiserum raised against rice strain (DGISP 183 Nepal). Bacterial suspensions (10⁸ cfu/ml) of 17 different strains in sterile phosphate buffered saline from 24-h-old cultures infiltrated to leaves of 2-month-old tobacco plants induced hypersensitive reaction after 24 h. Inoculated finger millet plants (21-day-old) showed blight and stripe symptoms after four to seven days. Acidovorax avenae subsp. avenae was re-isolated from such affected plants. The strains were gram-negative, non-fluorescent on King's medium B, arginine dihydrolase negative, nitrate-positive and starch-negative. Metabolic profiling of the strains using the Biolog GN MicroPlates and the associated MicroLog profiling matching software (Biolog Inc., Hayward, CA) identified strains as Acidovorax avenae. subsp. avenae (similarity 0.760 to 0.836). Strains are deposited at the DGISP culture collection, Copenhagen, Denmark. This is the first report of Acidovorax avenae subsp. avenae in finger millet from Uganda.