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First Report of Twig Canker on Peach Caused by Phomopsis amygdali in China

During May and June of 2009, canker and twig dieback were observed with 30 to 40% incidence in trees in one peach orchard in Nanhui of Shanghai (cv. YuLu juicy peach) and one orchard (cv. JingXiu yellow peach) in Jiaxin of Zhejiang Province, China. Cankers were generally centrally positioned on the nodes at the base of shoots with sunken, reddish brown/tan-to-silver symptoms. Blight was also observed on a few shoots (1). Five samples were collected from each orchard and isolations were conducted on potato sucrose agar (PSA). Ten isolates were obtained and all had white mycelia on PSA. Black pycnidia, formed in culture, produced two types of conidia: hyaline, fusiform alpha conidia and hyaline, string-like beta conidia. Alpha conidia varied from 5.0 to 6.3 × 1.5 to 2.5 μm and beta conidia ranged from 20 to 25 × 1.2 to 1.5 μm. Morphological characteristics suggested the identity of the fungal isolates to be Phomopsis amygdali. To confirm pathogenicity, an inoculum suspension was made from one isolate (10⁶ conidia/ml) and was sprayed until runoff onto five twigs with buds. Inoculated twigs were maintained at 26°C and 100% relative humidity in a growth chamber with a 12-h period of fluorescent light daily. Twigs inoculated with sterilized water were included as noninoculated controls. After 4 days, dark brown lesions appeared around buds on inoculated twigs. No symptoms were observed on the control twigs. Constriction cankers were reproduced and P. amygdali was reisolated from the lesions. To confirm the identity of the pathogen, total genomic DNA was extracted with the cetyltrimethylammoniumbromide (CTAB) method from the mycelia of two isolates from YuLu juicy peach and Jinxiu yellow peach (2). PCR was performed with universal primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) to amplify a DNA fragment of approximately 550 bp. The PCR products were purified and sequenced in both directions (Sangon Biotech (Shanghai) Co., Ltd., China). The sequences (GenBank Accession Nos. HQ632013 and HQ632014) shared 98.9% identity with each other (MegAlign software; DNASTAR, Madison, WI). A comparison of these two sequences with those in GenBank showed that the sequences had the highest nucleotide similarity (99%) with P. amygdali isolate FAU1052 from peach in the southeastern United States (Accession No. AF102998). To our knowledge, this is the first report of P. amygdali causing twig canker on peach in China and will provide useful information for developing effective control strategies.

References: (1) D. F. Farr et al. Mycologia 91:1008, 1999. (2) M. A. Saghai-Maroof et al. Proc. Natl. Acad. Sci. USA. 81:8014, 1984.