Resistance of strawberry genotypes to leather rot and crown rot caused by Phytophthora cactorum

Phytophthora cactorum causes crown rot of the strawberry rhizome and leather rot of strawberry fruit. Five strawberry cultivars, including two newly released cultivars (Nobel and Saga) from a Norwegian strawberry breeding program and eight selections from the same program, were tested for resistance to crown rot and leather rot and possible correlation in resistance between the two diseases. Strawberry fruit inoculated with P. cactorum had from below 40 to over 80 % of the surface covered with leather rot 4 days after inoculation. Cvs. Senga Sengana and Korona came out as relatively resistant (45 %), while cv. Polka was more susceptible (63 %). Nobel was the most susceptible to leather rot (83 %), while most selections and cv. Saga were intermediately resistant. For resistance against crown rot, the eight selections and two new cultivars varied between 3 and 6 on a scale from 1 to 8, where 1 was no disease development 4 weeks after inoculation and 8 was plant death 1 week after inoculation. Cvs. Nobel and Saga and the eight selections were intermediately to highly susceptible to crown rot, with the most resistant showing a level of resistance comparable to cv. Korona, which has previously been reported to be intermediately resistant. Cv. Nobel, which was most susceptible to leather rot was the second most tolerant to crown rot, and the selection that was most susceptible to crown rot was among the most resistant to leather rot. A Pearson correlation test showed that there was no correlation between resistance to crown rot and resistance to leather rot among the cultivars and selections included in this investigation.