New Disease Reports
New Disease Reports (2005) 12, 32.
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First report of crown rot of Photinia fraseri caused by Phytophthora cactorum

A.M. Vettraino 1, L. Antonacci 1, L. Flamini 2, P. Nipoti 3, E. Rossini 2, M. Righi 2 and A. Vannini 1*

*vannini@unitus.it

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Accepted: 10 Nov 2005

Photinia fraseri cv. Red Robin is an evergreen ornamental shrub belonging to the family Rosaceae. The species, probably of Asiatic origin, is utilised worldwide in gardens as an ornamental tree and shrub or to form garden hedges.

A survey carried out in 2004 in ornamental nurseries in the Marche region of Italy, revealed the presence of crown rot of potted plants of P. fraseri. Symptoms consisted in extended necrosis of leaf blade (Fig. 1). A Phytophthora spp. was consistently isolated from infected tissue plated on PARBhy (Pymaricin Ampicillin Rifampicin Benomyl hymexazol) medium at 18°C. Isolates developed white, slightly radiate colonies with aerial mycelium on potato dextrose agar. Sporangia were abundant, ellipsoid to ovoid with a conspicuous hemispherical papilla, caducous. Isolates appeared homothallic with thin walled spherical oogonia and nearly always paragynous antheridia. Isolates were identified as Phytophthora cactorum (Erwin & Ribeiro, 1996) using morphological features, RFLP and sequence analysis of ITS region of rDNA, with sequence homology searches of databases using BLAST (www.ncbi.nlm.nih.gov/BLAST).

Pathogenicity tests were conducted using a detached leaf dip assay as described by Denman et al. (2005) for P. ramorum. Two isolates of P. cactorum and 2 isolates of P. ramorum were used. Inoculation trials were carried out on non-wounded young and mature P. fraseri leaves. On inoculated leaves P. cactorum caused extensive blade necrosis (Fig. 2). No symptoms were recorded on leaves inoculated with P. ramorum and on negative controls under the experimental conditions used. P. cactorum was always reisolated from inoculated leaves.

P. cactorum is particularly aggressive to members of the Rosaceae family, on which it may cause root, collar and crown rot. A taxonomically-related species to P. fraseri, Heteromeles arbutifolia (syn. Photinia arbutifolia; common name toyon) has been reported to be a natural host of P. cactorum in the USA (Keim et al., 1976). This species is also reported to host P. ramorum. P. fraseri was recently reported as a foliar host of Phytophthora ramorum in Poland (Orlikowski et al., 2005).

To our knowledge this is the first record of P. cactorum on P. fraseri. The worldwide utilisation of P. fraseri and the common presence of P. cactorum on a broad range of hosts in nurseries represent a potential risk for easy spread of this disease.

Figure1+
Figure 1: Photinia fraseri cv. Red Robin plant with extensive leaf necrosis caused by Phytophthora cactorum
Figure 1: Photinia fraseri cv. Red Robin plant with extensive leaf necrosis caused by Phytophthora cactorum
Figure2+
Figure 2: Leaf necrosis of Photinia fraseri cv. Red Robin leaf artificially inoculated with Phytophthora cactorum
Figure 2: Leaf necrosis of Photinia fraseri cv. Red Robin leaf artificially inoculated with Phytophthora cactorum

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. Erwin DC, Ribeiro OK, 1996. Phytophthora Diseases Worldwide. St. Paul, USA: APS Press.
  3. Keim R, Mock T, Guenther H, 1976. Phytophthora crown rot of toyon. Plant Disease Reporter 60, 88-90.
  4. Orlikowski LB, Trzewik A, Szkuta G, 2005. Phytophthora ramorum on Calluna vulgaris, Photinia fraseri and Pieris japonica in Poland. In: Procedings of Sudden Oak Death Second Science Symposium, 2005. Berkeley, CA, USA: University of California, 118.
This report was formally published in Plant Pathology

©2005 The Authors