Molecular, physiological and pathological characterization of Corynespora leaf spot fungi from rubber plantations in Sri Lanka

The plant pathogenic fungus Corynespora cassiicola causes a severe leaf spot disease on more than 70 host plant species including Hevea brasiliensis . Genetic variability in 32 isolates of C. cassiicola collected from diverse hosts and locations in Sri Lanka and Australia was assessed using restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer (ITS) region of ribosomal DNA and random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) analysis of total fungal DNA. Amplified ITS fragments from all 32 C. cassiicola isolates exhibited an identical size, and restriction analysis with seven different restriction endonucleases revealed identity in all of the detected DNA fragments. This finding of high genetic relatedness was further supported by the cloning and DNA sequencing of the ITS2 region from one Sri Lankan and one Australian isolate. However, RAPD-PCR profiles generated by 15 oligonucleotide decamer primers revealed significant polymorphism between groups of organisms. Genetic relationships among the isolates were determined by cluster analysis of the RAPD-PCR data and seven different RAPD groups were identified. Isolates showed strong correlations between the assigned RAPD group and the location and host plant genotype from which the isolate was collected. Correlations were also observed between the RAPD group, growth of the isolate and pathogenicity on different plant hosts.