First Report of Phytophthora cactorum on Strawberry Plants in Spain

Crown rot of strawberry (Fragaria × ananassa Duch. cv. Camarosa) was observed in three and two production fields in 2000 and 2001, respectively, in Huelva, southwestern Andalucia, Spain. Affected plants did not exhibit typical symptoms of red stele. Instead, there was an internal red-brown discoloration of the upper crown, a bluish discoloration of leaves, and the plants were wilted. Eventually, plants collapsed and died. Fungi were isolated from surface-disinfested necrotic crown tissue on P₅ARPH medium (1). Plates were placed at 21°C for 5 to 10 days. One species was isolated consistently from symptomatic tissue. Microscopic observations revealed spherical oogonia with thin walls. Antheridia were paragynous and were attached to the oogonium near the oogonial stalk. Single oospores were spherical and had double-layered, yellow-brown walls (20 to 25 μm in diameter). Sporangia were usually borne terminally and were colorless and papillate (22 to 30 μm in diameter). Based on these characteristics, the causal agent was identified as Phytophthora cactorum (Lebert & Cohn) J. Schröt. (2). The fungus was transferred to V8 juice agar and maintained at 21°C in the dark. Disks (9-mm diameter) were removed from 7-day-old cultures of P. cactoru and used to inoculate five 2-month-old 'Camarosa' strawberry plants grown in sterilized peat in the greenhouse. Three disks were placed in the crown of each plant at soil level. Five noninoculated plants were similarly treated with sterile V8 juice agar disks only. After 2 weeks, the pathogen was reisolated from red-brown lesions visible on crowns of all inoculated plants. Noninoculated plants did not show any symptoms. To our knowledge, this is the first report of P. cactorum attacking strawberry plants in Spain. References: (1) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986. (2) G. M. Waterhouse and J. M. Waterston. No. 111 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, UK, 1996.