First report of Phytophthora ramorum on Rhododendron sp in Serbia

Abstract

In Europe Phytophthora ramorum has been reported on a range of ornamentals as well as on a limited number of tree species in at least in 11 countries: UK, Spain, Belgium, Germany, the Netherlands, Italy, France, Switzerland, Poland, Slovenia, France and Norway (http://rapra.csl.gov.uk). It is recorded mainly on Rhododendron but other hosts including Camellia, Kalmia, Pieris and Viburnum are also affected. This pathogen is regarded to be a potential source of inoculum for tree epidemics in Europe. In June 2008, symptoms resembling those of P. ramorum were observed on 12 specimens of Rhododendron sp. cv. Baden – Baden in an open garden in the vicinity of Zemun, Serbia. Plants with symptoms of leaf necrosis and blight and petiole necrosis were sampled and examined. Pieces of leaf tissue from the edge of lesions were surface-sterilized (70% ethanol) and placed on carrot piece agar, CPA (Werres et al., 2001). After 4–7 days incubation, isolates were slow growing with numerous semipapillate caducous sporangia ((35–80 (54) × 17–32 (26) μm) and large chlamydospores (average diameter 48 μm). The mating type was determined as A1, due to formation of typical sexual structures when crossed with A2 mating type of P. cinnamomi and P. cryptogea. The identity of the isolates was confirmed by PCR using Phyto1/4 primer pair (Hayden et al., 2004). A representative isolate (Pr92-08) was sequenced (GenBank Accession No. EU915480) and the ITS sequence was identical to other P. ramorum isolates on NCBI GenBank database. Pathogenicity was confirmed by inoculation of non-wounded detached leaves (Denman et al., 2005) of 15 different host plants. First necrotic spots were noticeable after 3 day incubation in moist chamber in laboratory on Rhododendron variegatum, R. morgenrot and Viburnum plicatum. The control leaves, inoculated with sterile water, showed no reactions. In all cases, the pathogen was successfully recovered from leaves with symptoms and also detected using PCR. This is the first report of P. ramorum on Rhododendron plants in Serbia. The infected plants were destroyed and measures were taken to eradicate the pathogen according to EU legislation. The discovery of infected Rhododendron plants should prompt more detailed surveys, thorough inspections and subsequent testing in other areas of Serbia.