Evaluation of methods of screening strawberry cultivars for resistance to crown rot caused by Phytophthora cactorum

Four methods were evaluated in measuring resistance of strawberry cultivars to crown rot caused by Phytophthora cactorum. Meristem propagated plants g rown in vitro were inoculated with mycelial discs. Four to five days after inoculation, it was possible to distinguish between cultivars with large di fferences in susceptibility to the disease. Ten days later, all plants were totally necrotic making it impossible to distinguish between cultivars. Wh en detached leaves were inoculated by inoculating a plug of mycelium into t he petiole, disease symptoms developed more slowly in resistant cultivars, but leaf age greatly affected the rate of symptom development. When plug pl ants (not cold stored) were lightly wounded in the rhizome with a scalpel a nd inoculated with either zoospores or mycelium, differences in disease dev elopment between cultivars were mainly as would be expected from previous i nformation on susceptibility, but both age and size of plants influenced th e rate of disease development. Unwounded, inoculated plants did not develop symptoms. When cold-stored plug plants were either unwounded or lightly wo unded with a scalpel in the rhizome and inoculated with zoospores, the rela tive rates of disease development consistently reflected the susceptibility to crown rot. At the time of final assessment, disease was much more sever e in wounded plants, but the relative susceptibility of cultivars was not a ffected by the wounding.