Articles
METHODS OF SCREENING RASPBERRIES FOR RESISTANCE TO PHYTOPHTHORA ROOT ROT
Cultivar resistance and incubation temperature had the greatest effect on the expression of symptoms.
Temperature could be used to distinguish between root rot caused by Phytophthora fragariae var. rubi and Phytophthora citricola: the former was highly pathogenic between 12 and 20 °C, while the latter had an optimum above 20 °C. Typical soil temperatures in raspberry growing regions indicate that Phytophthora citricola may only be of minor importance.
Other factors affecting symptom expression, in order of their importance, were plant size, inoculation method and inoculum density.
Differences in pathogenicity between isolates were small and no race-specific resistance could be observed.
Results obtained with the same cultivars in a greenhouse screen and in a field trial were very consistent with correlation coefficients (r) as high as 0.97. The screen should progress considerably the search for valuable root rot resistant cultivars of red raspberry.