First Report of Canker on Pecan (Carya cathayensis) Caused by Botryosphaeria dothidea in China.

Abstract

In the late 1990s, sporadic occurrence of Botryosphaeria canker on Carya cathayensis was recorded in Zhejiang Province, China. From 2005 to 2009, nearly 90% of orchards in Zhejiang and Anhui provinces were seriously affected by this disease. Symptoms were similar to those of canker of C. illinoinensis (2); small, elliptical lesions that developed on the bark at points of infection and then enlarged to form large, sunken, elongated cankers. The cankers coalesced, forming large diffuse areas of blighted tissue, which turned black. Tissue samples from the margin of trunk lesions from 35 different diseased trees from five counties were surface sterilized with 1.5% sodium hypochlorite for 3 min, plated on 2% potato dextrose agar (PDA), and incubated at 25°C in the dark for 1 week. Gray-black mycelia and colorless, aseptate, thin-walled conidia, 17.3 ± 0.8 long and 4.5 ± 0.5 μm wide, were produced. On the basis of these morphological characteristics, the fungus was identified as Botryosphaeria dothidea (Moug. ex Fr.) Ces. & De Not (1). The internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 from DNA extracted from mycelium produced on PDA and was recorded as GenBank Accession Nos. HQ731442 and HQ731443. The results of BLAST showed that it had more than 98% similarity to records for B. dothidea. Uninfected twigs and stems of C. cathayensis were wounded with a scalpel and then sprayed with a conidia suspension of 106 conidia per ml in distilled water as inoculum or distilled water only to provide an noninoculated control, wrapped in plastic bags to retain moisture, and incubated for 48 h. For each isolate, five twigs and stems per tree and a total of 10 trees were inoculated. After 2 weeks, 14 of 15 isolates caused lesions on inoculated stems and twigs, whereas no symptoms developed on the noninoculated controls. Cultures isolated from lesions and cultured on PDA exhibited morphological characteristics identical to those of B. dothidea, confirming completion of Koch's postulates. Currently, the distribution of Botryosphaeria canker of C. cathayensis is confined to Zhejiang and Anhui provinces. The identification of the pathogen now allows for appropriate forest management measures. To our knowledge, this is the first report of Botryosphaeria canker of pecan (C. cathayensis) in China.