CRYPHONECTRIA CANKER OF EUCALYPTUS
MJ WINGFIELD and BD WINGFIELD
Tree Pathology Co-operative Programme, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0002, South Africa
Background and objectives
Cryphonectria cubensis is one of the most serious canker pathogens of Eucalyptus in the tropics and sub-tropics . Losses in seedling stands, have led to the introduction of vegetative propagation, and the deployment of disease tolerant hybrids. Using this approach, the impact of cryphonectria canker has been substantially reduced. However, selection of disease tolerant planting stock is generally based on field observations. Very little is known about the pathogen, its origin, genetic diversity or its capacity to overcome disease tolerance in selected clones. The aim of this report is to briefly review studies aimed at reducing the impact of cryponectria canker, particularly in South Africa, but also elsewhere.
Results and conclusions
Symptoms of crypohonectria canker in South Africa are somewhat different to those in other parts of the world, which is intriguing. Inoculation studies in South Africa, Indonesia and South America also suggest that the South African isolates of C. cubensis have a different biology to those from the other countries. In South Africa, inoculation of clones gives a clear view of their relative susceptibility, prior to commercial deployment. This is a useful tool for forest managers and it is now being evaluated in Indonesia and various South American countries. Through artificial inoculation, eucalypt genotypes representing a range of tolerance to C. cubensis have been identified and introduced into breeding studies. The resultant parents and progeny are now being used to develop rapid DNA-based screening techniques.
Although it is not viewed as an alternative to breeding and selection of disease tolerant clones, biological control of C. cubensis through dsRNA mediated hypovirulence could be useful. This would especially be true in countries such as South Africa where C. cubensis appears to be recently introduced and represented by a limited genetic diversity. dsRNA has recently been discovered in South African and Brazilian isolates of C. cubensis and is currently being studied. The potential to utilise C. cubensis isolates transfected and/or transformed with ds RNA from Cryphonectria parasitica, is also being considered.