Chinese hickory is an important forest crop in Anhui and Zhejiang provinces of China. In a survey conducted from 2010 to 2013, serious trunk disease was revealed on C. cathayensis in Ningguo city, Anhui Province. In 2013, nearly 20% of hickory orchards and 5% of hickory trees were affected in this region. Symptoms observed from May to November included dark brown bark lesions and bark cracking on trunks. Bark cracks increased in size over time (mostly more than 80 cm long), extending into the phloem and leading to extensive areas of bark loss with discoloration of the underlying xylem. In most cases, infected plants died within 2 to 4 years. Infected samples collected from 16 orchards in Nanji town and 8 orchards in Hule town were surface sterilized with 1.5% sodium hypochlorite for 2 min, plated on potato dextrose agar (PDA), and incubated at 25°C in the dark for 1 week. Eleven similar isolates were obtained from diseased trunks. Colonies reached 7.5 cm diameter after 7 days on PDA at 25°C. Fungal colonies were white with sparse aerial mycelium. Acervuli containing black, slimy spore masses on the surface were present after 12 days at 25°C. Conidia were fusiform to clavate with five cells, 17.5 to 22.5 × 5.2 to 6.4 μm. Apical and basal cells were colorless, while the middle cells were heterochrome; the upper two middle cells were darker than the lower one (3). There were two or three hyaline filamentous appendages (mostly two), 14.5 to 20.6 μm long, attached to each apical cell, and one hyaline appendage (3.5 to 6.6 μm long) attached to each basal cell. Cultural and morphological characteristics of these isolates matched the genus description for Pestalotiopsis (2). The universal rDNA-ITS primer pair ITS4/ITS5 was used to amplify a DNA fragment of approximately 633 bp. The amplified PCR products were sequenced and compared through BLASTn analysis. Sequences of all isolates were identical and 99% similar to Pestalotiopsis vismiae (GenBank Accession Nos. FJ481027.1 and AB251916.1) and P. hansenii. The sequence of isolate RCEF6350 was deposited in GenBank (KM015217). Morphological features best match P. vismiae and with the supporting molecular data, the pathogen was identified as P. vismiae. To confirm pathogenicity, conidial suspensions (106 conidia ml−1) of each of two isolates were inoculated in three holes (0.5 cm in diameter) drilled to the cambium of each of 12 trees (15 years old). Distilled water was the control. Holes were wrapped with wet absorbent cotton and Parafilm. After 30 days, 62.5% of the inoculated trees developed symptoms similar to natural infections of P. vismiae, whereas control trees remained symptomless. P. vismiae with identical morphology was re-isolated from the lesions to complete Koch's postulates. Therefore, P. vismiae was identified as the causal agent for trunk disease of C. cathayensis in China. P. vismiae was previously reported as a pathogen of Myrica rubra (1); to our knowledge, this is the first report of P. vismiae as a pathogen on Chinese hickory in China.
References: (1) F. Y. Chen et al. Plant Dis. 96:588, 2012. (2) Q. X. Ge et al. Flora Fungorum Sinicorum. Vol. 38, Pestalotiopsis. Science Press, Beijing, 2009. (3) J. X. Zhang. Master's thesis, Zhejiang University, Hangzhou, 2003.