Production of polygalacturonases in isolates of Cryphonectria cubensis of differing pathogenicity

Percy M. Chimwamurombe¹*, Brenda D.Wingfield_², Anna-Maria Botha² and Michael J. Wingfield²

¹Department of Biology, University of Namibia, Post Bag - 13301, Windhoek (Namibia). ²Forest and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria - 0002, (South Africa)

ABSTRACT: Cryphonectria cubensis causes a serious stem canker disease on Eucalyptus in tropical and subtropical parts of the world. Previously, it was shown that isolates of C. cubensis display varying levels of pathogenicity. The aim of this study was to consider whether a relationship exists between the production levels of polygalacturonases and pathogenicity in isolates of C. cubensis. Seven isolates of C. cubensis known to have differing levels of pathogenicity were assessed for polygalacturonase production using agarose gel diffusion and reducing sugar assays. Our results showed that the levels of polygalacturonase production are not significantly different in natural isolates of C. cubensis that have different pathogenicity levels. However, in one hypovirulent isolate, CMW6009, which has been artificially transfected with hypovirus CHV1-713 from Cryphonectria parasitica, a delay of six days in the production of polygalacturonases was observed. We conclude that polygalacturonases probably have a minor role in determining the pathogenicity of the C. cubensis. Furthermore, the hypovirus CHV1-713 that causes hypovirulence in C. cubensis, has a major role in controlling pathogenicity and its mechanism of action may involve disruption of the production of polygalacturonases and other cell wall degrading enzymes.

KEYWORDS: Eucalyptus; Cryphonectria cubensis; polygalacturonases

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