Phytophthora ramorum on Calluna vulgaris, Photinia fraseri and Pieris japonica in Poland

Leszek B. Orlikowski, AleksandraTrzewik, Res. Institute of Pomology & Floriculture, Pomologiczna 18, 96-100 Skierniewice, Poland, lorlikow@insad.pl; Grazyna Szkuta, State Plant Health and Seed Service Inspection Service, Zwirki i Wigury 73, 87 – 100 Torun, Poland

After recovery of P. ramorum from rhododendron and cowberry (Vaccinium vitis-idaea) in 2000 – 2002 (Orlikowski & Szkuta 2002), disease symptoms were observed on 3 other ornamentals July-August 2003. Symptoms usually occurred after at least 3 drizzly days 18 - 23ºC. On heather (Calluna vulgaris), symptoms were observed only on cv. Peter Sparkes. Shoot apices turned brown to dark brown for 2-5cm. Older invaded shoots formed shepherd’s crooks. On Photinia (Photinia fraseri), symptoms were observed only on leaves. Petioles were dark brown and necrosis spread on blades. On some leaves brown or dark brown spots were observed at the apex or middle of leaf blades. Spots usually enlarged and leaves fell quickly. On leaf spots transferred to moist chambers, 1–2 mm brown-black drops appeared within 2–3 days at 20–22ºC. Pieris shoot symptoms were similar to rhododendron. Morphological and molecular methods indicated P. ramorum, with the A1 mating type. The pathogen grew best at 20-25ºC (range 2–28ºC). After pairing 3 test isolates with A2 mating type P. cryptogea, generative structures formed. Three isolates from heather, Photinia, Pieris and 3 cultures from rhododendron caused similar lesions. Most rhododendron and heather cultivars inoculated with P. ramorum isolates developed necrotic symptoms.

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