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Bacterial Leaf Spot and Stem Collapse of Mung Bean Caused by Pseudomonas syringae pv. syringae. M. W. George, Plant Science Division, University of Idaho, Moscow 83843-4196. R. R. Tripepi, Plant Science Division, University of Idaho, Moscow 83843-4196. Plant Dis. 74:394. Accepted for publication 15 February 1990. DOI: 10.1094/PD-74-0394E.

Collapsed upper stems and necrotic spots on leaves were observed on mung bean (Vigna radiata (L.) R. Wilczek 'Berken') seedlings grown for rooting bioassays. A gram-negative, rod-shaped bacterium was consistently isolated from symptomatic stem tissue. The bacterium was identified as Pseudomonas syringae pv. syringae van Hall based on: 1) production of levan, a hypersensitive reaction in tobacco, a green diffusible fluorescent pigment on King's medium B, and syringomycin as determined by the inhibition of Geotrichum candidum Link ex Pers. growth (1); 2) use of mannitol, inositol, sorbitol, and L-lactate as sole carbon sources; and 3) negative responses for oxidase production, soft rot in potato, and halo blight on bean pods. To fulfill Koch's postulates, lO-day-old mung bean seedlings were stab-inoculated with a 104 cfu/ml bacterial suspension. At 28 C, typical symptoms developed within 3 days after inoculation, and the same bacteria were reisolated from diseased seedlings. The pathogen was seedborne, because approximately 10% of seedlings that grew from surface-sterilized seeds became diseased within 9 days. This is the first report of a disease in mung bean caused by P. s. pv. syringae.

Reference: (1) D. C. Gross and J. E. DeVay. Phytopathology 67:475, 1977.