Scopoletin (7-hydroxy-6-methoxy coumarin) which inhibited the conidial germination of Corynespora cassiicola was isolated from the uninfected mature leaves of Hevea brasiliensis. Scopoletin was not detected in uninfected immature rubber leaves. The immature leaves produced scopoletin after being infected with C. cassiicola. The concentration of scopoletin in infected leaves was higher than in uninfected mature leaves. Scopoletin also inhibited the conidial germination of other fungal pathogens of H. brasiliensis. However, no correlation was observed between scopoletin accumulation and clonal resistance.
Ascomycota/drug effects , Hevea/metabolism , Hevea/microbiology , Plant Leaves/chemistry , Scopoletin/isolation & purification , Scopoletin/pharmacology , Antifungal Agents/isolation & purification , Antifungal Agents/metabolism , Antifungal Agents/pharmacology , Ascomycota/growth & development , Hevea/chemistry , Plant Diseases/microbiology , Plant Leaves/metabolism , Plant Leaves/microbiology , Scopoletin/metabolism
Corynespora cassiicola is the causal organism of the most devastating leaf disease of rubber in Sri Lanka. Cotton, cowpea, cucumber, eggplant, sesame, soybean, tobacco, and tomato also have been reported as hosts of C. cassiicola. In Sri Lanka, however, the fungus has been reported only on rubber, soybean, winged bean, and tomato (1). During this investigation, C. cassiicola was isolated from cocoa, tomato, papaya, winged bean, sweet potato, and manihot. The pathogenicity of each isolate on the host from which it was isolated was established by following Koch's postulates. This is the first record of Corynespora leaf disease on cocoa, papaya, sweet potato, and manihot in Sri Lanka. Using an aqueous spore suspension (5 × 104 spores per ml), rubber leaves were inoculated separately with each isolate. Inoculation studies indicated that, except for the isolate from papaya, all isolates also were pathogenic on rubber. In Sri Lanka all the host plants listed are commonly cultivated in and around rubber plantations. Therefore, the existence of C. cassiicola infections on other hosts should be taken into account when developing control measures for Corynespora infection on rubber. Reference: (1) P. Shivanathan and R. S. Y. de Silva. 1989. Plant pests of Sri Lanka. Rep. Plant Quarantine Div. 1989. Plant Quarantine Division, Peradeniya. Sri Lanka.
