Population diversity among Brazilian isolates of Cryphonectria cubensis

The devastating effect of Cryphonectria canker on Eucalyptus spp. in Brazil has necessitated the initiation of a strategy to control the disease. A po tential biological control strategy for Cryphonectria cubensis would be to make use of dsRNA, capable of debilitating the fungus. However, success wou ld depend on the diversity of the pathogen population. In this study, the p resence of vegetative compatibility groups (VCGs) in C. cubensis was demons trated by pairing isolates and observing the reaction along the line of con tact between the expanding colonies. Isolates (1092) of C. cubensis, from 1 82 Eucalyptus trees located in five regions in Brazil, were examined using this method. On a tree, one or at most two VCGs were present. However, isol ates from different but closely spaced trees, represented numerous VCGs. It is probable that the multiplicity of VCGs in the Brazilian population of C . cubensis will limit the natural spread of dsRNA and, hence, limit the pot ential for biocontrol via hypovirulence. The large number of VCGs is also i ndicative of st well-established, and possibly endemic population of the pa thogen. (C) 1998 Elsevier Science B.V. All rights reserved.