Inhibition of fungal polygalacturonases by extracts of Eucalyptus grandis with different disease susceptibilities

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

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

ABSTRACT: Eucalyptus grandis is an important exotic forest plantation species in many parts of the world. Diseases caused by fungal pathogens are an important constraint to the productivity of Eucalyptus plantations. Fungi secrete cell wall degrading enzymes (CWDEs) during the process of colonising plants. Endopolygalacturonases (endoPGs) constitute some of the important CWDEs. The aim of this study was to detect and compare the levels of polygalacturonases produced by a group of different Eucalyptus pathogens. A further objective was to determine the inhibition levels of polygalacturonase-inhibiting proteins (PGIPs) associated with a disease tolerant and a susceptible Eucalyptus clone on endoPGs from the fungal pathogens. Extracts of the polygalacturonases were collected from selected isolates of the Eucalyptus canker pathogens Cryphonectria cubensis, Coniothyrium zuluense, Botryosphaeria dothidea and the root pathogen Phytophthora cinnamomi. Polygalacturonase production and inhibition by PGIPs was measured by reducing sugar assays. We found that B. dothidea and C. zuluense produced more endoPGs than C. cubensis and P. cinnamomi. In most cases PGIPs from the generally disease tolerant clone were equally as effective as those from the susceptible clone, in their capacity to inhibit the endoPGs. An exception was for C. zuluense, where PGIPs from the resistant clone were considerably more effective than those from the susceptible clone. We conclude the PGIP extracts from Eucalyptus selectively inhibit endoPGs from different species. The tolerance of the resistant clone to C. zuluense could be linked to the ability of its PGIPs to inhibit endoPGs from C. zuluense.

KEYWORDS: Eucalyptus grandis; polygalacturonases; PGIPs; host defence

[ HTML Full Text]