Bacterial wilt of common bean (Phaseolus vulgaris L.) caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Hedges) Collins & Jones (4) was found in 1947 in Ontario, Canada (3), but not in western Canada. Infected seeds exhibit yellow, orange, or purple discoloration (4). Examination of 36.7 kg of cull beans of crops grown in southern Alberta in 2001 obtained from a processing plant revealed 5.9% yellow and 0.014% orange seeds, each with wrinkled seed coats. Bacteria were isolated on potato dextrose agar. Three strains were identified using conventional tests (2), carbohydrate oxidation (GP Microplates, Biolog Inc., Hayward, CA), and cellular fatty acids (CFA) (MIDI, Inc., Newark, DE). Strains were gram-positive, motile, aerobic rods with yellow (YSB-1, YSB-2) or orange (OSB-3) colonies. Growth occurred at 27 and 37°C. The strains were positive for citrate utilization, catalase, hydrolysis of hippurate, and indoxyl acetate, and negative for urease, gelatin liquification, and oxidase. CFA profiles were ≈48% 15:0 anteiso, 37% 17:0 anteiso, 8% 16:0 iso, 3% 15:0 iso, and 3% 16:0; with17:1 anteiso A sometimes present at <2%. Acid production was weak from carbohydrates, but all oxidized many carbohydrates in the microplates. These results match C. flaccumfaciens pv. flaccumfaciens (2) in MIDI and Biolog databases. Strains were tested for pathogenicity using seed and pod inoculations. Seeds of great northern (‘US1140’) and navy (‘AC Skipper’) beans were soaked in bacterial suspension (1 to 3 × 108 CFU/ml) for 1 h, sown in Cornell Peatlite Mix (1) in Root Trainers (Spencer-Lemaire Industries, Edmonton, AB, Canada), incubated at 28°C (16-h day) and 22°C (8-h night), and examined for seedling wilt after 10 days. Seeds soaked in sterile distilled water served as controls. Testing was repeated once with 3 replicates per treatment and 10 seeds per replicate. Experiments were conducted using a complete randomization design. For pod inoculation, a suspension (0.1 ml) of each strain was injected into the midrib at the basal end of each young pod of ‘AC Skipper’. Pods inoculated with sterile distilled water, 0.1 ml per pod, were used as controls. After 21 days, pods were harvested and examined. Testing was repeated once with three plants per treatment and five pods per plant. Bacteria were reisolated from hypocotyls of wilted seedlings and diseased pods. Results of seed inoculations showed all strains were pathogenic to both cultivars. Wilt incidence was 38, 35, and 57% for strains YSB-1, YSB-2, and OSB-3, respectively, on ‘US1140’ and 44, 40, and 63% respectively, on ‘AC Skipper’. Results of pod inoculations showed 63% (YSB-1) and 55% (YSB-2) of seeds had wrinkled, yellow seed coats, and 72% (OSB-3) of seeds had wrinkled, orange seed coats. Control seedlings and seeds remained healthy. C. flaccumfaciens pv. flaccumfaciens was reisolated from wilted seedlings and seeds showing yellow or orange discoloration, but not from the controls. To our knowledge, this is the first report of bacterial wilt of bean caused by yellow and orange strains of C. flaccumfaciens pv. flaccumfaciens in western Canada.
References: (1) J. W. Boodley and R. Sheldrake Jr. N.Y. State Coll. Agric. Life Sci. Inform. Bull. 43, 1977. (2) K. Komagata et al. Page 1313 in: Bergey's Manual of Systematic Bacteriology, Vol. 2, Williams and Wilkens, Baltimore, MD, 1986. (3) Z. A. Patrick, Can. J. Bot. 32:705, 1954. (4) A. W. Saettler. Bacterial wilt. Page 31 in: Compendium of Bean Diseases. R. Hall, ed. American Phytopathology Society, St. Paul, MN, 1994.
