Screening Plant Resistance to Phytophthora cactorum with the Dipping Test

Resistance of strawberry cultivars to crown rot (Phytophthora cactorum) has been evaluated at MTT Agrifood Research Finland since 1993 using the crown test and the NFT test. The crown test is quick and reliable and the test with running irrigation water gives results as quickly as the crown test. The NFT system is, however, expensive and the viability of Phytophthora zoospores can be reduced or completely lost if the hydroponic environment contains substances that are harmful to them. Inoculation by dipping the tray plants in P. cactorum inoculum was investigated to solve this problem. The inoculum concentration was the same as previously used in the NFT test. Inoculation in Vefi pots seemed to give the same result as addition of sporangia to circulating irrigation water, but symptom expression was delayed during the first two test weeks. Crown rot developed within 4 weeks and a longer test time did not change the level of infection. According to the tests on cultivars 'Jonsok', 'Kimberly' and 'Polka', inoculation in Vefi pots with zoospores is effective and can save costs in the greenhouse environment.