Eleutherococcus senticosus (Acanthopanax senticosus, manyprickle acathopanax) is a perennial herb belonging to the family Araliaceae and is mainly distributed in northeastern China, Siberia, Korea, and Japan. It is used for the treatment of rheumatism and neurasthenia. With the development of its cultivation, many diseases began to occur (2) and a previously unknown leaf blight on manyprickle was first observed in July of 2010 in Linjiang City, Jilin Province. The same symptoms were detected in other areas of Jilin Province, such as Baishan and Hunchun cities. The disease has resulted in serious loss of production of manyprickle acanthopanax, with 5 to 10% of leaves infected. The infection initially manifested as irregular lesions on the tips or margins of the leaves, which gradually developed into a V-shaped blight with concentric rings that was grayish brown in the center and dark brown at the margins. The blight eventually spread to cover one third of the entire leaf. Severely infected leaves were rolled or distorted, eventually desiccated and became brittle. Under continuously humid conditions, scattered gray mycelium and conidia appeared on the surface of affected leaf tissue. To isolate the causal agent, tissues were excised from diseased leaves, immersed in 0.1% mercuric chloride, suspended in sterile water, and plated on potato dextrose agar (PDA). Conidiophores arose singly or in groups, straight or flexuous, septate, with an inflated basal cell and dendriform near the apex, brown to light brown, and measured 5.0 to 10.0 × 100.0 to 150.0 μm (n = 50). Conidia were single-celled, globoid or oval-shaped, colorless, measuring 6.0 to 10.0 × 7.0 to 13.0 μm (n = 50). In culture, dark, irregular sclerotia were produced. The morphological descriptions and measurements of the fungi were similar to Botrytis cinerea (4). The ITS region of rDNA was amplified and sequenced. BLAST analysis of the 567-bp segment (JX840481) showed 100% identity with the sequence of Botryotinia fuckeliana (perfect stage of B. cinerea). To further identify the species of B. cinerea, three nuclear protein-coding genes (G3PDH, HSP60, and RPB2) (3) were sequenced and the sequences (KJ018759, KJ018757, and KJ018755) all showed 100% identity with those of B. fuckeliana. Pathogenicity tests were carried out on potted, healthy, 1-year-old plants (n = 10). A conidial suspension of 105 conidia/ml was sprayed with each strain (five strains total) on five leaves still on plants, and five plants were sprayed with water as controls. Plants were covered with polyethylene bags and incubated for 3 days at 25°C in a greenhouse. Symptoms appeared 7 days after inoculation, and were similar to those originally observed on plants under natural conditions, whereas control plants remained healthy. The pathogen was successfully re-isolated from inoculated leaves and was identified as B. cinerea on the basis of its morphological characteristics and related gene sequences. B. cinerea has been previously reported on E. senticosus in Korea (1). However, to our knowledge, this is the first report of Botrytis leaf blight of E. senticosus caused by B. cinerea in China. These results lay the foundation for the disease control.
References: (1) K. J. Choi et al. Korean J. Med. Crop Sci. 15:199, 2007. (2) J. Gao et al. Plant Dis. 95:493, 2011. (3) M. Staats et al. Mol. Biol. Evol. 22:333, 2005. (4) Z. Y. Zhang. Flora Fungorum Sinicorum. 26. Botrytis, Ramularia. Science Press, Beijing, 2006.