PHYTOPHTHORA: AN INTRODUCED HAZARD IN FORESTS, WOODLANDS AND WOODY HEATHS
Forestry and Forest Products, CSIRO, PO Wembley 6014, Western Australia
Background and objectives
Results and conclusions
Large differences exist in the susceptibility amongst species, both between and within some species of native plant genera. Conservation for biodiversity of the genetic structure of native host species is an important consideration in managing this disease. In infected sites, individuals of plant species at the very susceptible end of the scale do not survive to set seed; others species regenerate predominantly by vegetative growth so that in some communities all the woody species are replaced by resistant sedges and annuals. In species with some field resistance, population resistance may be enhanced by natural selection or promoted by management introductions of more resistant forms from selection and breeding programs. Resistance in native vegetation involves non-co-evolved host-pathogen associations and it is most probably due to general and not host-specific genetic resistance factors. Disease control in long-lived woody plants is a long-term venture. Programs selecting and breeding for disease resistance in native forest, woodland and heath species are challenged by the need to develop long-term resistance.
Resistance to P. cinnamomi in a wide range of woody species can be enhanced by foliar spraying with low concentrations of phosphite. Phosphite remains effective for more than 4 years in species having slow growth rates and high biochemical recycling of nutrients. It provides an option for disease management in native vegetation, especially for rare and endangered communities. It does not kill the pathogen in soil, but appears to reduce propagule production of treated plants (Shearer & Komorek, personal communication).
Phosphite application, deploying resistant plants, quarantine measures and other types of disease management are a considerable cost to the community. This is particularly so when control must be achieved in large tracts, often on public lands serving many, sometimes conflicting, interests including timber production, recreation, biodiversity and conservation.