RISKS AND THREATS DUE TO GENETIC VARIATION IN PHYTOPHTHORA CINNAMOMI FOR DISEASE MANAGEMENT IN NATURAL VEGETATION ECOSYSTEMS

Phytophthora cinnamomi is often genetically diverse in disease fronts and diseased areas. P. cinnamomi has considerable ability to produce a wide range of pathogenic phenotypes measured from ‘plant clone by isolate by environmental factor interactions ’ in each of the three pathogen clonal lineages of P. cinnamomi isolated in Australia. P. cinnamomi lineages are defined by microsatellite types. In a few disease areas, despite both mating types occurring in the same square metre of soil, or 50 g soil sample or bait plant, no evidence of sexual reproduction (genomic recombination) has been found in the field. Isolates are sexually competent in the laboratory and all lineage combinations are strongly outcrossing. Hence the substantial variation in lineages in a range of traits associated with disease development must be arising asexually. Preventing movement of any P. cinnamomi contaminated material is critical to maximising disease control and minimising risks of introducing new strains which may threaten plant communities, their diversity and the integrity of these ecosystems. Phosphite or other intended phytophthoracide usage, which does not eliminate P. cinnamomi in plant nurseries can, by camouflaging disease, increase potential risks and threats by spreading different strains in diseased materials