Variability in the Resistance of Banksia L.f. Species to Phytophthora cinnamomi Rands

Resistance of Banksia species to Phytophthora cinnamomi was determined under plantation conditions for 39 Western Australian and 10 eastern Australian Banksia spp. Plants were inoculated twice using millet seed inoculum, at the start of the study and 95 days later. To test for intraspecific variants or escape from disease, surviving individuals were stem-inoculated with P. cinnamomi. Infection in plant tissues was confirmed by reisolation with selective media. Horticulturally exploited species including B. hookerana, B. coccinea, B. prionotes, B. occidentalis, B. baxteri, B. sceptrum, B. speciosa, B. grandis, B. menziesii and B. victoriae were found to be suscep- tible to P. cinnamomi. Eight eastern Australian species showed resistance (95% survival). Seven West- ern Australian species including all prostrate species tested were found to have low susceptibility. There was a poor correlation between levels of susceptibility and taxonomic series in the genus, particularly in eastern and western component species of the pan-Australian series Orthostylis and Spicigerae. Banksia spp. from uniform or summer maximum rainfall regions were resistant or of low susceptibility while those from dominantly winter rainfall areas, especially with free draining soils, were highly sus- ceptible. Stem inoculation confirmed that one plant each of B. coccinea and B. hookerana was resistant among the P. cinnamomi-susceptible, horticulturally exploited species. Thus stem inoculation proved a useful diagnostic tool, and girdling rather than longitudinal fungus growth through stem tissue is more appropriate as a measure of species' resistance.