Sensitivity of Hevea brasiliensis clones to isolates representing distinct races of the Corynespora cassiicola pathogen

Corynespora leaf fall disease caused by the fungus Corynespora cassiicola is a major leaf disease of Hevea brasiliensis, the commercial source of natural rubber. Different clones of H. brasiliensis show varying levels of sensitivity towards different strains of C. cassiicola. The genetic mechanism behind the differential sensitivity of H. brasiliensis clones has to be identified in order to develop clones resistant to wider range of C. cassiicola strains. The available information on the sensitivity of H. brasiliensis clones is based on the observation of natural infection or infection of detached leaves. In the present study, the sensitivity of seven H. brasiliensis clones towards two strains of C. cassiicola belonging to two different races was determined using a more precise method by artificial infection of the plants under controlled conditions. Strain CLN 16 was found to be more virulent compared with CSB 16, as it induced more severe symptoms in a shorter period. Among the four different stages of leaves, Stage II leaves with copper brown to apple green colour showed higher sensitivity to both strains followed by Stage III leaves with apple green appearance. Among the clones, RRIM 600 had a higher susceptibility towards CSB 16; however, it was the most resistant clone towards CLN 16. Clone PB 350 showed the highest susceptibility towards CLN 16 whereas RRIM 928 showed the highest resistance towards CSB 16. The present study provides a platform for further studies leading to the development of H. brasiliensis clones with resistance towards wider range of C. cassiicola strains.