New Disease Reports
New Disease Reports (2008) 18, 31.
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First report of Phytophthora ramorum on Rhododendron sp. in Serbia

A. Bulajić 1*, J. Jović 2, S. Krnjajić 2, I. Djekić 1 and B. Krstić 1

*aleksandrabulajic@yahoo.com

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Accepted: 18 Nov 2008

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 trees 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-sterilised (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) x 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 Acc. 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 symptomatic leaves, the pathogen was successfully recovered and 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.

Figure1+
Figure 1: Symptoms of Phytophthora ramorum on leaves and petiole of Rhododendron sp.
Figure 1: Symptoms of Phytophthora ramorum on leaves and petiole of Rhododendron sp.
Figure2+
Figure 2: Semipapillate sporangia and chlamydospores of Phytophthora ramorum
Figure 2: Semipapillate sporangia and chlamydospores of Phytophthora ramorum

Acknowledgements

We thank Dr S. Werres for providing mating type tester isolates and M. Žerjav for providing reference isolates.

References

  1. Denman S, Kirk SA, Brasier CM, Webber JF, 2005. In vitro leaf inoculation studies as an indication of tree foliage susceptibility to Phytophthora ramorum in the UK. Plant Pathology 54, 512 – 521.
  2. Hayden KJ, Rizzo D, Tse J, Garbelotto M, 2004. Detection and quantification of Phytophthora ramorum from California forests using real–time polymerase chain reaction assay. Phytopathology 94, 1075 – 1083.
  3. Werres S, Marwitz R, Man in’t Veld WA, De Cock AWAM, Bonants PJM, De Weerdt M, Themann K, Ilieva E, Baayen RP, 2001. Phytophthora ramorum sp. nov., a new pathogen on Rhododendron and Viburnum. Mycological Research 105, 1155 – 1165.
This report was formally published in Plant Pathology

©2008 The Authors