Evaluation of the 'Dome Test' as a Reliable Assay for Seedborne Bacterial Blight Pathogens of Beans. L. K. Lahman, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. N. W. Schaad, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. Plant Dis. 69:680-683. Accepted for publication 30 January 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-680.

Samples of 15 bean seed lots were assayed by 'dome test' procedures for Pseudomonas syringae pv. syringae (P. syringae), P. syringae pv. phaseolicola (P. phaseolicola), Xanthomonas campestris pv. phaseoli pv. phaseoli), and X. campestris pv. phaseoli var. fuscans. Some seed lots were chosen because they were positive in dome tests elsewhere. Bacteria were isolated from lesions of bean seedlings in a dome test. Bacteria producing a white, flat, nonmucoid fluorescent colony or yellow-mucoid colony on King et al’s medium B and yeast extract-dextrose calcium-carbonate agars, respectively, were purified. Identities of possible pseudomonad blight pathogens were verified by utilization of manitol, sorbitol, and lactate, levan formation, oxidase reaction, and pathogenicity. Possible xanthomonads were verified by pathogenicity tests. Thirty-one fluorescent colonies and 66 yellow-pigmented colonies were isolated from 11 and 8 of the 15 seed lots, respectively. Neither P. phaseolicola nor X. phaseoli were identified in the 15 seed lots, and P. syringae was identified in only one of the 15 seed lots. However, six pseudomonads that failed standard pathogenicity tests produced water-soaking when injected into seedlings kept under dome test conditions. These results suggest that the dome test is not a reliable assay procedure for issuing phytosanitary certificates.