In December 2004, symptoms of root and crown rot were observed on cucumbers (Cucumis sativus L.) in a greenhouse in Norway. Cucumbers were the only crop of the greenhouse that used rockwool as a growing substrate in a hydroponical system. The first symptoms were detected in propagation material. One week after planting, symptoms of root and crown rot were observed and approximately 10% of the plants died. Later, losses of 50% in some greenhouses were observed. A yield reduction as much as 65% was estimated in the winter period (January and February). The two main cucumber cultivars planted were Armada and Lopez. In February 2005, Phytophthora capsici (Leonian) (1) was isolated on potato dextrose agar from a sample of cv. Lopez. The isolate produced deciduous, papillate sporangia (occasionally with two or three papilla) and pedicels that were sometimes longer than the sporangia. Sequencing of amplicons of the internal transcribed spacer region (ITS) rDNA and of the mitochondrial cytochrome c oxidase subunit 1 (Cox1) gene (2) confirmed the identification. Three isolates collected through 2005 from the same greenhouse were crossed with tester strains of P. cryptogea. Formation of oogonia and amphigynous antheridia was always observed in crosses with mating type A2; thus, all isolates were the A1 mating type. All three isolates grew well at 35°C and did not produce chlamydospores. A pathogenicity test was performed with one isolate of P. capsici. Four plants of cucumber cvs. Indira and Jessica were grown in a growth chamber at 24°C. Plants at the two-leaf stage were drenched with 20 ml of a zoospore suspension of 106 zoospores per ml per plant. After 18 days, all plants of both cultivars developed symptoms of crown rot or wilted and died. P. capsici was reisolated from inoculated plants of both cultivars. The pathogenicity test was repeated in the same way, but in a greenhouse with temperatures that ranged between 18 and 29°C. In addition, four plants of both cultivars at the four-leaf stage were inoculated with a suspension of 105 zoospores per ml. After 1 week, all plants developed crown rot or were irreversibly wilted, independently of the plant age or the zoospore concentration. To our knowledge, this is the first report of P. capsici in Norway.
References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society St. Paul MN, 1996. (2) L. P. N. M. Kroon et al. Phytopathology 94:613, 2004.
