A Modified Procedure for Assaying Bean Seeds for the Pathogen Causing Bacterial Brown Spot and Results of Assays of Commercial Bean Seeds

Disease severity was recorded 2 weeks after planting when seedlings were still at the primary leaf stage. In all of the rows planted with inoculated seeds, some of the plants were symptomless and others had leaf spots and puckering symptoms characteristic of bacterial brown spot. No difference in type or severity of symptoms was noted in any of the treatments. None of the treatments resulted in severe disease at this early stage, but all caused either slight or moderate levels of disease. None of the uninoculated plants had any brown spot symptoms. Symptoms were not recorded later because of concern that they could have been induced by inoculum that had spread from plants inoculated by other means. The peat carrier with the high level of bacterial suspension was used in a preliminary study of the comparative ability of four strains of the pathogen to cause disease on the susceptible and resistant snap bean cultivars Bush Blue Lake 47 and Bush Blue Lake 94, respectively. In this trial, the inoculum, was applied to seeds of a susceptible cultivar that were planted in "spreader rows" between rows of the susceptible and resistant cultivars. The pathogen spread from inoculated plants to uninoculated plants in adjacent rows and" induced disease. The results of this trial were inconclusive. However, the inoculation procedure worked extremely well. Therefore, we recommend using laboratory-produced inoculum instead of dried-leaf inoculum in breeding trials because it overcomes the disadvantages described earlier for leaf inoculum.