Development of a screening method for resistance to Phytophthora cactorum

In The Netherlands the fungus Phytophthora cactorum, which causes crown rot in strawberry plants, has become a problem. Because of high losses of plants and the difficulty of chemical control, resistant cultivars are wanted. Therefore we wish to develop an efficient, reliable and fast screening method, which can be used for breeding and for determining the Value for Cultivation and Use (VCU) with regard to Plant Variety Rights. In previous research cultivars were screened by a "crown-test", which is destructive, inaccurate and very laborious. So a new method was developed using a hydroponic system (NFT). Runners of different cultivars were planted out in rockwool plugs, followed by artificial inoculation of the NFT system with a spore suspension of P. cactorum. The resistance level was determined by the period between infection and plant death. Large differences in resistance between cultivars were found. Susceptible cultivars started dying ten days after infection. Highly resistant cultivars were still apparently healthy after 90 days. Results corresponded well with earlier experiences. The test proved to be sufficiently accurate for testing cultivars.