Genetic variation among isolates of Rigidoporus microporus causing white root disease of rubber trees in Southern Thailand revealed by ISSR markers and pathogenicity

The genetic variation among 32 isolates of Rigidoporus microporus was determined using pathogenicity tests and molecular marker (intersimple sequence repeats; ISSR). Isolates were collected from six sites of two provinces in the south of Thailand. Based on the pathogenicity results, all isolates could divide into three groups depended on their virulence to rubber trees as follows: low virulent isolates, moderately virulent isolates and high virulent isolates. Cluster analysis based on ISSR characters grouped the isolates according to geographical origins. A dendrogram resulting from a cluster analysis showed two main distinct groups, designated as A and B rooting from outgroup. Group A contained isolates collected from Surat Thani province and group B those collected from Narathiwat province. There was no clear relationship between degrees of disease and geographical regions.