Genetic Variation and Phytotoxin Production among Cylindrocladium. Quinqueseptatum Isolates of Hevea Brasiliensis and Eugenia Carryophyllata

Abstract

Cylindrocladium quinqueseptatum (Boedijn & Reitsma 1950) is one of the major plant pathogenic fungi that infects a wide range of plants in humid tropics. The prevailing strains in Sri Lanka cause the foliage and shoot blight diseases and severe defoliation of Hevea brasiliensis (rubber) and Eugenia carryophyllata (clove). The isolates obtained from rubber and clove plants growing in Rathnapura district, in Sabaragamuwa province and Kalutara district, in Western province were evaluated for their toxin activity on hosts and genetic characterization was done using random amplified polymorphic DNA Polymerase Chain Reaction (RAPD-PCR grouping). The analysis of the results using ‘Wilcoxon signed-rank test’ revealed no correlation among the isolates based on their host or geographical origins. But a relationship was observed between the toxin activity and the RAPD grouping of the isolates. The time course experiment reveled that the minimum toxin activity recorded after three days of inoculation and maximum toxin activity was recorded after nine days of inoculation in Modified Fries Medium (MFM) for all the isolates. Based on the toxin activity and genetic characterization data, the isolates were categorized into two groups. The close genetic relationship (similarity index = 0.731) and high toxin activity were shown by one group of isolates obtained from cloves grown in Rathnapura with other two groups of isolates obtained from rubber grown in Kalutara. This observation suggests that C. quinqueseptatum isolated from clove grown in Rathnapura can be a potential pathogen on rubber.