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First Report of Stem Rot of Konjac Caused by Phytophthora nicotianae in China

February 2015 , Volume 99 , Number  2
Pages  283.2 - 283.2

M. Shao, W. F. Du, D. C. Yu, P. Du, S. J. Ni, Y. C. Xu, and H. J. Zhang, Key Laboratory for Agro-Biodiversity and Pest Control of the Ministry of Education, College of Plant Protection, Yunnan Agricultural University, Kunming,650201, China

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Accepted for publication 13 October 2014.

Konjac (Amorphophallus) is an important economic crop widely used in health products and biomaterials in Asia (2). A serious foliage disease of Konjac was observed in Fuyuan County, Yunnan Province, China, in July 2012. The symptoms began with leaf color changes from light green to yellow, followed by discoloration on the stem base, plant wilting, bulb rotting, and ultimately plant death. Symptomatic tissues were cut into small pieces, surface-sterilized, and cultured on 20% V8 juice agar at 28°C. Five days after incubation, white fluffy colonies with the typical sporangium of Phytophthora sp. were observed from root and stem pieces. Isolates were identified as P. nicotianae based on morphological characteristics and DNA analysis. The growth rate of the colonies was 16 mm/d at 28°C. Sporangia were pyriform, ovoid to spherical, and papillate, and the dimensions of the 80 sporangia measured ranged from 23.7 to 60.4 × 19.4 to 45.7 μm (avg. 42.4 × 31.5 μm) with length-to-breadth ratios of 1.19 to 1.44 (avg. 1.34). The chlamydospores were spherical with a smooth surface, and their dimensions ranged from 20.3 to 47.3 × 18.9 to 45.9 μm (avg. 32.7 × 30.4 μm) (3). DNA was extracted from one colony containing spores and hyphae of the isolated P. nicotianae, and the nuclear ribosomal DNA internal transcribed spacer (ITS) region was amplified with primers ITS6 and ITS4 (4). The obtained 854-bp amplicon was purified and sequenced. NCBI BLAST retrieved a 100% identity with P. nicotianae (GenBank Accession No. KJ506732). A pathogenicity test of the isolated P. nicotianae was conducted in a greenhouse. After 7 days in a humidity-controlled greenhouse, all 10 inoculated plants showed similar symptoms as observed initially in the field, while control plants were symptomless. P. nicotianae was re-isolated from the inoculated stems, thus successfully completing Koch's postulates (1). To our knowledge, this is the first report of P. nicotianae as a pathogen of Konjac in China.

References: (1) B. Alvarez-Rodriguez et al. Plant Dis. 97:1257, 2013. (2) H. Ban, et al. Plant Cell Rep. 28:1847, 2009. (3) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. APS Press, St. Paul, MN, 1996. (4) J. M. French et al. Plant Dis. 95:1028, 2011.

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