Phenolic and Lignin Concentration as an Indicator of Resistance to Phytophthora Cinnamomi in Banksia Species

Phytophthora cinnamomi Rands, a soilborne fungus, is regarded as one of the most devastating pathogens yet recorded in natural ecosystems. The disease, caused by P. cinnamomi, poses an enormous threat to the flora of the southwest. The Proteaceae, in particular, contribute considerably to species richness and provide the fundamental floristic structure of many south-western plant communities. The genus Banksia, a member of the Proteaceae, is very susceptible to disease caused by P. cinnamomi. Three species, namely B. attenuata, B. grandis and B. menziesii. Were established in an aeroponics system under glasshouse conditions. Trials were conducted to optimise growing conditions in these systems and to determine the most effective method of inoculation. Shoots were treated with a 0.5% phosphonate foliar spray and roots were dipped in P. cinnamomi zoospore suspensions. The temporal, spatial and treatment changes in the concentrations of total soluble phenolics and lignin in roots, four and twelve days after inoculation, were measured. Total soluble phenolics decreased in inoculated treatments compared with controls. In addition, phenolic levels were even lower by twelve days after inoculation. In comparison, lignin concentrations did not have a significant effect on these compounds in B. menziesii, however, it increased in inoculated plants above control levels. Phosphonate application B. grandis produced increased levels of total soluble phenolics with phosphonate application. This study aimed at developing an understanding of the biochemical defences of Banksia species to Phytophthora, enables the resistance of these species to be compared and assessed.