Report of New Symptoms of Corynespora Leaf Fall Disease from the Non-traditional Rubber Growing Areas in Sri Lanka

Abstract

Hevea brasiliensis (natural rubber) is one of the major economically important plantation crops in Sri Lanka. Traditionally, rubber was grown mainly in the wet zone of the country. Currently, the cultivation is being expanded to the intermediate and dry zone. These new rubber growing areas are known as non-traditional rubber growing areas. Corynespora leaf fall disease is regarded as the most destructive foliar disease and the disease has caused a major devastation in rubber industry resulting in a remarkable economic lass of Sri Lankan rubber industry. The causative agent is the fungus, Corynespora cassiicola. Characteristic symptom of the fungus on rubber leaves is the “railway track lesion”. Later more than ten different symptoms have been reported for this disease. The symptom varied based on the type of clone, maturity level and also on the environmental condition. Due to this reason, the disease identification has become complicated especially among the field staff. This study was carried out to report newly produced symptoms of this disease. Twelve different symptoms have been illustrated with the most characteristic symptom. In this study to collect Corynespora leaf disease samples from non-traditional rubber growing areas among the lesion and unusual symptoms was observed from Padiyathalawa. Then the fungus was isolated on to PDA. Later single spore isolation technique was employed to purify the culture. Koch’s postulates were proven. The fungus was identified as based on cultural and reproductive characteristics. The newly reported symptom is illustrated to aid disease diagnosis.
Keywords: Hevea brasiliensis, Non-traditional areas, Symptoms, Corynespora cassiicola, Foliar disease