ABSTRACT
Phytophthora ramorum was found for the first time in Finland during the spring of 2004 on marketed plants of Rhododendron spp. originating in other EU member states. During August of 2004, the pathogen was also found in one Finnish nursery on German Rhododendron catawbiense plants and several Finnish Rhododendron spp. cultivars. P. ramorum was detected by species-specific PCR and isolated (1). It was first characterized by an abundant production of chlamydospores on PARP and V8 agar, absence of oogonia and antheridia, and elongate, ellipsoid, deciduous, semipapillate sporangia produced in soil extract water (3). A partial sequence of the ß-tubulin gene was identical to that of P. ramorum deposited in GenBank. Despite strict regulations governing the movement of plants, the pathogen has been found every year since 2004 on materials transported to Finland from other EU countries. A total of 586 samples were taken from symptomatic plants of several susceptible species from 2004 to 2006. P. ramorum was detected in 51 rhododendron samples and the number of the outbreak sites was 28. In domestic plant production, P. ramorum was found in only one nursery. The infected plants in this nursery were destroyed in 2005 according to the EU regulation 2004/426/EG. During the 2006 growing season, 84 samples from trace-forward inspections and reinspections of the nursery were tested and P. ramorum was not detected in any of the samples. In 2005, surveys for P. ramorum on Finnish Rhododendron spp. cultivars with necrotic lesions on leaves and blackened tips yielded, in addition to P. ramorum, another Phytophthora sp. On V8 agar, this homothallic species showed a stellate growth pattern with sparse aerial mycelium. Oogonia had both paragynous and amphigynous antheridia, and sporangia produced in soil extract water were ellipsoid in shape and semipapillate. A 763-bp segment of the ß-tubulin gene was sequenced and was identical to the ß-tubulin sequence of P. inflata strain IMI342898 (GenBank), which was isolated in 1990 from Syringa sp. in the UK. It is likely that this P. inflata strain has been spreading in Europe with the ornamental plant trade. To fulfill Koch's postulates, rhododenrdon plants were inoculated (2) with P. inflata or P. ramorum, typical symptoms observed, and the pathogens were reisolated from inoculated plants. Both Phytophthora species also caused necrotic lesions on Alnus glutinosa, A. incana, and Betula pendula. Pinus sylvestris was resistant to both Phytophthora spp., whereas Picea abies was susceptible to P. inflata but not P. ramorum. References: (1) EPPO Bull. 36:145, 2006. (2) E. Hansen et al. Plant Dis. 89:63, 2005. (3) S. Werres et al. Mycol. Res. 105:1155, 2001.
ABSTRACT
Strawberry (Fragaria × ananassa) is the most important small fruit crop in Finland. The quarantined pest Colletotrichum acutatum was detected for the first time on strawberry in August 2000, in Eastern Finland. Waiting-bed plants of cultivar Elsanta had symptoms typical of anthracnose rot (black spot) on the fruit, and small black lesions were seen on stolons. The rainy, warm, and humid weather of the summer favored the development and spread of the disease. C. acutatum was isolated from lesions on the fruit. Abundant sporulation was observed on lesions, and the fungus was readily isolated on potato dextrose agar (PDA) from surface-sterilized fruit pieces. Spores (11.5 to 19.8 × 3.3 to 4.0 µm) were acute at both ends, and acervuli with salmon pink spore masses matched the descriptions of C. acutatum (1). At first, the colonies were white and later became ash gray. The growth rate of the fungus was 8.0 to 8.8 mm per day, at 27°C. The identification was confirmed with enzyme-linked immunosorbent assay at the Central Science Laboratory, York, U.K. In order to fulfill Koch's postulates, young potted strawberry plants were inoculated by misting with a suspension of 10.4 × 106 conidia per ml of C. acutatum. Healthy runner plants of micropropagated cultivars Bounty, Cudaruska, Jonsok, Korona, and Oka (10 plants of each cultivar) were inoculated and incubated for 3 days, at 100% relative humidity. After 3 weeks at 20 to 21°C and 16 h of light per day, dark, elongated lesions measuring 2 to 15 mm were observed on the stolons. All tested cultivars developed symptoms on stolons and petioles, but no crown infections were detected. Flowering and fruit-bearing plants of cultivars Honeoye, Sara, and Senga Sengana were similarly inoculated and incubated. The first symptoms of fruit rot were detected 5 days after inoculation on the ripening fruit of Honeoye. Less severe fruit rot was seen on the fruit of Senga Sengana and the Fragaria vescana cultivar Sara. Salmon pink sporodochia developed on infected fruit, stolons, and leaves, within 5 days on moist filter paper, and C. acutatum was isolated on PDA. No other pathogens were present. Because C. acutatum is a quarantined pest in Finland, all strawberry plants of the infected lot on this particular farm were destroyed and future use of the field will be restricted. Reference: (1) C. M. Howard et al. 1992. Plant Dis. 76:976-981.
