Evaluation of Banksia species for response to Phytophthora infection

Phytophthora cinnamomi was the species isolated most frequently from soil associated with dead or dying proteaceous plants in the Adelaide region of South Australia. The association of P. citricola with diseased Banksia species in South Australia is reported for the first time. The response of a range of Banksia species to inoculation with P. cinnamomi and P. citricola was assessed. P. cinnamomi was generally more pathogenic than P. citricola . Inoculation of 10-month-old seedlings with colonized millet seed or zoospores showed that B. hookeriana and B. ashbyi were the most susceptible of the species tested, whereas B. coccinea , B. menziesii and B. prionotes were moderately susceptible. B. ericifolia , B. serrata , B. spinulosa var. collina and B. lemanniana showed tolerance. Similarly, 2–3-week-old seedlings of B. ericifolia , B. serrata and B. spinulosa var. collina inoculated in vitro showed little disease 6 and 12 days after inoculation, whereas B. baueri, B. baxteri , B. coccinea and B. solandri , as well as B. hookeriana and B. ashbyi , showed severe symptoms of disease after 6 days. Results suggested that 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. spinulosa var. collina inoculated in vitro with zoospores of P. cinnamomi . Roots of B. coccinea and B. menziesii were colonized rapidly and root tips became necrotic within 24 h and hypocotyls by day 5. Penetration was delayed in B. spinulosa var. collina , and callose deposition was delayed in B. coccinea . Necrosis of roots of B. serrata and B. spinulosa var. collina began 3 days after inoculation but rarely extended more than half way up the root by 9 days.