Almond (Prunus dulcis) production is currently increasing in Turkey. Losses of approximately 1% associated with root and crown rot of almond seedlings were observed in two commercial nurseries in Ankara and Düzce provinces in 2009. Aboveground symptoms were leaf chlorosis and wilt. Feeder roots were decayed, necrosis occurred on taproots and basal stems, and plants collapsed within several weeks. Roots were washed in tap water and 9 to 10 pieces (3 to 5 mm long) of root tissue taken from the margins of canker lesions, without surface disinfection, were placed on selective medium P5ARPH-CMA (2). Plates were incubated for 3 to 5 days at 20°C in darkness and a number of Phytophthora spp. were recovered. Actively growing mycelium was transferred to carrot piece agar containing β-sitosterol (per liter: carrot piece, 40 g; agar, 20 g; β-sitosterol, 20 mg). Isolates were identified as Phytophthora cactorum and P. citrophthora on the basis of morphological characteristics (1). P. cactorum produced abundant sporangia, oogonia, and paragynous antheridia on carrot piece agar plus β-sitosterol. It had conspicuously papillate and caducous sporangia with short pedicel. Sporangia were usually ovoid but sometimes nearly spherical. P. citrophthora did not produce sexual structures in single culture. It produced papillate, noncaducous sporangia, which were usually ovoid and obpyriform, often asymmetrically shaped and rarely possessed more than one apex. P. citrophthora did not grow at 35°C but it grew well at 30°C. Isolate identities were confirmed by sequence analysis of the ribosomal DNA internal transcribed spacers 1 and 2 (GenBank Accession Nos. HM357622, HM357623, HM357624, HM357625) using primers ITS1 and ITS2 (3). One representative isolate of each species was used to inoculate eight 2-year-old almond plants with an agar plug with actively growing mycelium that was attached to exposed cambium of basal stems. Agar plugs without mycelium were used for eight control plants. All plants inoculated with Phytophthora spp. collapsed within 3 to 4 weeks. Control plants remained healthy. Phytophthora spp. were reisolated from necrotic basal stems. To our knowledge, this is the first report of P. cactorum and P. citrophthora of almond in Turkey.
References: (1) M. E. Gallegly and C. Hong. Phytophthora, Identifying Species by Morphology and DNA Fingerprints. The American Phytopathological Society, St. Paul, MN, 2008. (2) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986. (3) S. G. Roy et al. J. Phytopathol. 157:666, 2009.
