Influence of Inoculum Density, Wetness Duration, Plant Age, Inoculation Method, and Cultivar Resistance on Infection of Pepper Plants by Colletotrichum coccodes

Abstract

Effects of inoculum density, wetness duration, plant age, inoculation method, and cultivar resistance on the development of pepper anthracnose caused by Colletotrichum coccodes were evaluated under controlled environmental conditions. As inoculum density of C. coccodes increased from 103 to 106 conidia/ml, symptoms of anthracnose developed. Disease severity also increased with increasing time of wetness duration from 0 to 60 h. Wetness duration above 48 h and a high inoculum density at 106 conidia/ml caused severe defoliation and blight symptoms in pepper seedlings. Inoculum at 104 conidia/ml and 24 to 36 h of continuous wetness duration was enough to form irregular or circular brown lesions on pepper leaves. Age-related resistance was expressed as pepper plants matured. To evaluate resistance, the foliar-inoculation method was more reliable than the soil-drench method, which did not induce symptoms on older plants. The responses of 35 pepper cultivars or accessions tested to C. coccodes were quantitative rather than qualitative. No hypersensitive symptoms were observed in any of the cultivars inoculated with any of the two isolates. No significant differences in susceptibility to anthracnose were found among cultivars from Korea, the United States, India, and Thailand or accessions tested, irrespective of genetic or country origin of cultivars. The Korean cultivar Kwangbok was relatively less susceptible to anthracnose, compared with the other cultivars tested