EVALUATION OF BANKSIA SPECIES FOR RESPONSE TO PHYTOPHTHORA INFECTION

Phytophthora cinnamomi was the species isolated most frequently from s oil associated with dead or dying proteaceous plants in the Adelaide r egion of South Australia. The association of P. citricola with disease d Banksia species in South Australia is reported for the first time. T he response of a range of Banksia species to inoculation with P. cinna momi and P. citricola was assessed. P, cinnamomi was generally more pa thogenic than P. citricola. Inoculation of 10-month-old seedlings with colonized millet seed or zoospores showed that B. hookeriana and B. a shbyi were the most susceptible of the species tested, whereas B. cocc inea, B. menziesii and B. prionotes were moderately susceptible. B. er icifolia, B. serrata, B. spinulosa var. collina and B. lemanniana show ed tolerance. Similarly, 2-3-week-old seedlings of B. ericifolia, B. s errata and B. spinulosa var. collina inoculated in vitro showed little disease 6 and 12 days after inoculation, whereas B. baueri, B. baxter i, B. coccinea and B. solandri, as well as B. hookeriana and B. ashbyi , showed severe symptoms of disease after 6 days. Results suggested th at the in vitro assay may have potential in the evaluation of breeding material. Development of infection was studied microscopically in 2-3 -week-old seedlings of B. coccinea, B. menziesii, B. serrata and B. sp inulosa var. collina inoculated in vitro with zoospores of P. cinnamom i. Roots of B. coccinea and B. menziesii were colonized rapidly and ro ot tips became necrotic within 24 h and hypocotyls by day 5. Penetrati on was delayed in B. spinulosa var, collina, and callose deposition wa s delayed in B. coccinea. Necrosis of roots of B. serrata and B. spinu losa var. collina began 3 days after inoculation but rarely extended m ore than half way up the root by 9 days.