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Zhang C.Q.,Zhejiang University | Xu B.C.,The Forest Pest Control Station of Hangzhou Municipal
Plant Disease | Year: 2012

Chinese hickory (Carya cathayensis) has become one of the important economic forest crops in Zhejiang and Anhui Provinces in China. In May 2009, sporadic occurrence of leaf damage by anthracnose in C. cathayensis was observed in Lin'an city, Zhejiang Province. During May 2011, nearly 50% of Chinese hickory orchards in Zhejiang Province were affected by anthracnose disease. Symptoms were extensive with lesions on stems and leaves. Under wet conditions, orange masses of conidia were produced in acervuli in the center of lesions. Infected tissue samples were surface sterilized with 1.5% sodium hypochlorite for 1.5 min, plated on 2% potato dextrose agar (PDA), and incubated at 26°C in the dark for 1 week. Developing colonies were gray and contained masses of orange conidia. Conidia were hyaline, aseptate, straight with rounded or bulbous ends, and averaged 15.3 ± 1.7 μm long and 2.5 ± 0.8 μm wide. The ribosomal internal transcribed spacers ITS1 and ITS2 were amplified with primers ITS1/ITS4 from DNA extracted from mycelium and nucleotide sequences showed 100% similarity to records for C. gloeosporioides in GenBank (Accession Nos. AY266391.1 and JQ676187.1). Uninfected leaves of C. cathayensis were sprayed either with a conidia suspension of 107 conidia per ml in distilled water as inoculum, or with distilled water only to provide an uninoculated control, wrapped in plastic bags to retain moisture, and incubated for 24 h. For each isolate, 10 leaves per tree and a total of 13 trees were inoculated. After 1 week, 11 of 13 isolates caused lesions on inoculated leaves whereas no symptoms developed on the non-inoculated controls. Cultures reisolated from lesions and cultured on PDA exhibited morphological characteristics identical to those of C. gloeosporioides (1, 2, 3), confirming Koch's postulates. Inoculation tests were repeated once. Since C. gloeosporioides was found in the main production area, it poses a threat to Chinese hickory production in China. The identification of the pathogen now allows for appropriate management measures. To our knowledge, this is the first report of anthracnose in C. cathayensis. Source


Liu Y.H.,Zhejiang University | Zhang C.Q.,Zhejiang University | Xu B.C.,The Forest Pest Control Station of Hangzhou Municipal
Plant Disease | Year: 2013

Chinese hickory (Carya cathayensis) is one of the important economic forest crops in Zhejiang and Anhui Provinces, China. In 2012, nearly 40% of hickory orchards and 6.8% of hickory trees were affected by leaf blight in Zhejiang. Initial symptoms consisted of small, brown, water-soaked lesions, which subsequently enlarged and developed a black sporulating necrotic center surrounded by a chlorotic halo. Infected leaf samples collected from 25 different orchards in Lin'an and 13 different orchards in Chun'an were surface sterilized with 1.5% sodium hypochlorite for 1.5 min, rinsed in water, plated on 2% potato dextrose agar (PDA), and incubated at 25°C in the dark for 1 week. Single conidium cultures were consistently isolated and cultured on PDA and V8 agar for morphological characterization (1,3). On both agar media, colonies were dark olive brown with smooth margins and concentric rings of sporulation. Conidia were solitary, darkly pigmented, predominantly ovoid-subsphaeroid, and 23 to 52 × 13 to 23 μm with up to six or seven transepta and one to three longisepta. The ribosomal internal transcribed spacers ITS1 and ITS2 of 10 isolates were amplified using primers ITS1/ITS4 on DNA extracted from mycelium and nucleotide sequences showed 100% similarity to that of A. petroselini (GenBank Accession Nos. AY154685.1 and EU807868.1). To confirm pathogenicity, 10 uninfected leaves from each of 10 C. cathayensis trees were sprayed either with a conidia suspension (105 conidia per ml) or with distilled water only to serve as an un-inoculated control. Leaves were subsequently wrapped in plastic bags to retain moisture, and incubated for 48 h. After 1 week, 8 of 10 isolates caused lesions identical to those initially described whereas no symptoms developed on water inoculated leaves. Cultures reisolated from lesions and cultured on PDA exhibited morphological characteristics identical to A. petroselini (1,2,3), confirming Koch's postulates. To our knowledge, this is the first report of leaf blight in C. cathayensis, and this identification would allow producers to identify for appropriate management practices. © The American Phytopathological Society. Source


Zhang C.Q.,Zhejiang University | Liu Y.H.,Zhejiang University | Wu H.M.,Zhejiang University | Xu B.C.,The Forest Pest Control Station of Hangzhou Municipal | And 2 more authors.
Crop Protection | Year: 2012

Pestalotiopsis microspora is the cause of the nut black spot of Chinese hickory (Carya cathayensis), which seriously threatens nut production in China. In this work, the baseline sensitivity of P. microspora to pyraclostrobin, a QoI fungicide, was studied and highly resistant isolates (HRI) to pyraclostrobin were characterized biologically and pathologically. Pyraclostrobin showed a high activity against P. microspora in vitro, with effective median concentrations (EC50) of 0.92 mg l-1 and 0.08 mg l-1 for mycelial growth and conidium germination inhibition, respectively. The EC50 determined for a total of 165 isolates of P. microspora collected from three geographical regions of China between 2007 and 2009 varied from 0.01 to 0.25 mg l-1 (mean of 0.13 ± 0.04 mg l-1) following a unimodal distribution. Five HRI to pyraclostrobin, obtained after expose the mycelium to UV light, were cross-resistant to azoxystrobin, another QOI fungicide. However, no cross-resistance was obtained against boscalid, a fungicide having a different mode of action. Interestingly, the HRI were less virulent than their sensitive wild parents, but no difference between HRI and their sensitive wild parents were obtained in mycelia growth, conidial production and conidial germination. These results indicated that pyraclostrobin might be a good fungicide alternative to control the nut black spot of Chinese hickory. © 2012 Elsevier Ltd. Source

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