Bean anthracnose:: Inoculation methods and influence of plant stage on resistance of Phaseolus vulgaris cultivars

Bean anthracnose, caused by Collelotrichum lindemuthianum, severely reduces bean production world-wide and rapid methods are required to investigate bean-C. lindemuthianum interactions. In this study, bean cvs Boterkoning, Saxa and Admires were inoculated with C. lindemuthianum race 69 using three different methods: germinated seed inoculation, seedling inoculation and detached leaf inoculation. Although the methods gave similar results, inoculation of detached leaves was the best method. In order to compare the susceptibility of bean at different developmental stages, cvs Prelude, Boterkoning, Saxa and Admires were used. Leaves harvested from 6-, 8-, 10-, 12- and 14-day-old plants were inoculated with C. lindemuthianum races 9, 69, 385, and 401. Race 9 was virulent to the four bean cultivars at all the tested stages; cvs Admires and Saxa were resistant to races 69, 385 and 401, whereas cv. Boterkoning was susceptible. Plants of cv. Prelude were sensitive at 8 days of age, but resistant when 12 and 14 days old. The present results suggest that the resistance of certain bean cultivars is not equally expressed at all the developmental stages.