Response of Phaseolus vulgaris protoplasts to chemical components of fungal origin

Colletotrichum lindemuthianum is the causal agent of anthracnose in Phaseolus vulgaris L. (French bean). The α and β races of the fungus were used in this study with French bean cultivar ‘Great Northern’. Whole plants inoculated with the α race developed brown lesions on the hypocotyls (susceptible response). The β race caused small limited lesions, indicating a more resistant interaction. Extracellular products and cell wall materials were isolated from β race cultures and extracellular products from α race cultures. The extracts were size fractionated. By using a cotyledon bioassay, elicitor activity was demonstrated on ‘Dark Red Kidney’ within fractions from the α race. Fractions from the β race had little activity on ‘Dark Red Kidney’ or ‘Great Northern’ cotyledons. Protoplasts were isolated from ‘Great Northern’ bean hypocotyl tissue and incubated with the fungal fractions. Even at low concentrations (0.01 μg glucose equivalent∙mL−1), the β race culture filtrate rapidly killed a greater percentage of protoplasts (30%) than the α race (15%). The β race wall extract had little effect upon protoplast viability. The proportion of nonviable protoplasts depended on the incubation period and the concentration of the fungal material. Heat treatment of the culture filtrates and wall extract did not decrease their lethal effects. The results suggest that protoplasts may be valuable in examining the nature of certain plant–pathogen interactions.