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Identification of Races of Pseudomonas Syringae pv. Phaseolicola Present in North Dakota
April 01, 2001


R. S. Lamppa and P. L. Gross,
Department of Plant Pathology, NDSU, Fargo, ND

Nine races of Pseudomonas syringae pv. phaseolicola (Psp), which causes halo blight, have been identified. Races 1,2,6 and 7 have been found to have worldwide distribution with race 6 being the most common.

Psp was isolated in 2000 from diseased dry edible bean leaves and pods collected from fields in ten North Dakota counties: Dickey, Foster, Grand Forks, Griggs, Nelson, Richland, Sargent, Steele, Traill and Walsh. These 122 Psp isolates plus six from 1995, three from 1997 and ten from 1999 made up the collection used in the identification of races present in North Dakota.

The Psp isolates were identified by standard biochemical tests; fluorescence on Kings B medium, Gram reaction, levan production, oxidase reaction, arginine dihydrolase production, and pectinase activity. Pathogenicity on dry edible bean was determined using the dark red kidney cultivar Charlevoix.

Race identification was achieved by observing the compatible or incompatible reaction to the inoculation of eight differential bean cultivars. Inoculation was done by airbrushing a bacterial suspension (c. 108cfu/ml) into and onto the underside of the primary leaves. After inoculation the plants were kept in a moist chamber for 24 hours and then returned to the greenhouse. Plant infections were scored 10 days after inoculation using a 1 to 5 scale with 1 being highly resistant and 5 being highly susceptible. The differential cultivars and control Psp cultures for race identification were obtained from South Africa where work has been done on race identification of Psp.


A predominant number of isolates were identified as race six. Race 6 was identified 133 times, race 2 identified twice, and 6 isolates gave results that could be considered between races 6 and 2. The results of the study suggests that there is not a large variability in the population of  Pseudomonas syringae pv. phaseolicola present in North


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