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Bacterial Blight of Soybeans as Influenced by Populations of Yellow Bacteria on Leaves and Buds. R. H. Scherff, Research Plant Pathologist, Plant Science Research Division, Agricultural Research Service, U.S. Department of Agriculture, University of Missouri, Columbia 65201; Phytopathology 63:752-755. Accepted for publication 27 December 1972. DOI: 10.1094/Phyto-63-752.

A bacterium characteristic of a group of yellow bacteria was isolated from soybean leaves infected with Pseudomonas glycinea and designated as YB-3. It is a small, gram-negative rod that has a polar flagella, is highly motile, oxidase-positive, and produces a light yellow, water insoluble pigment. When P. glycinea was mixed with YB-3 at a 1:9 ratio and inoculated onto soybean leaves, lesion development of bacterial blight was inhibited; at a 1:4 ratio, there was ca. 50% reduction in symptoms, and at a 1:1 ratio there was no reduction in lesion development. By incubating the 1:4 mixture of P. glycinea:YB-3 24-48 hr before inoculating the leaves, complete inhibition of bacterial blight symptoms resulted. Population levels of P. glycinea and YB-3 were assayed 1, 2, 3, 7, and 14 days after atomizing mixtures of them onto uninjured leaf surfaces. Seven days after application of P. glycinea:YB-3 at a 1:9 ratio there was a sharp reduction in the number of P. glycinea cells; whereas when a 1:1 mixture of P. glycinea and YB-3 or P. glycinea alone was applied, the number of P. glycinea cells increased. Numbers of YB-3 increased slightly through day 3 but dropped sharply thereafter. When mixtures of P. glycinea: YB-3 at a 1:9 ratio were placed on soybean buds, YB-3 multiplied more rapidly than did P. glycinea. From day 3 throughout the remainder of the test period, the number of YB-3 cells remained at the same level but P. glycinea cell numbers decreased.