INVESTIGATIONS ON THE PREDISPOSITION OF STRAWBERRY PLANTS TO CROWN ROT (PHYTOPHTHORA-CACTORUM)

Predisposition of strawberry plants to crown rot was investigated by using fresh plants and frigo plants. The susceptibility of uninjured frigo plants changed characteristically during the first period of growth. Immediately after thawing and a few days later the plants were resistant or slightly susceptible. Then susceptibility increased and was highest 12 days after thawing. Mortality was always low with uninjured frigo plants. Frigo plants injured by frost were highly susceptible from the beginning and showed a high mortality rate. Uninjured frigo plants and fresh plants became infected only when the rhizome was wounded. Usually, only fresh wounds could be infected. However, infections were often observed on older wounds of fresh plants wilting due to transplanting stress. The rhizomes of frost-injured frigo plants were infected at a high rate without being wounded. The rhizome of such plants also became infected via roots, petiols, and flower stalks. This was not the case with uninjured frigo plants and fresh plants.