First Report of Gray Mold on Amorphophallus muelleri Caused by Botrytis cinerea in China

Abstract

Amorphophallus muelleri is a perennial tuberous plant in the family Araceae. The name konjac is commonly used for the species of genus Amorphophallus that produce a polysaccharide, glucomannan. The latter, called konjac glucomannan, is extracted from the tubers of these species. Glucomannan is an excellent gelling agent used in food, pharmaceutical and chemical industry, a specialty crop grown as a source of glucomannan for industrial use. It is an important cash crop and thus contributes to poverty alleviation in southwest China. Its planting area is about 150 million mu (10 million ha). In July 2012, symptoms of an unknown blight were observed on 5 to 10% of A. muelleri flowers and seeds being grown for commercial seed production. Greenhouses temperatures ranged from 20 to 34°C (avg. 26°C). A light grey mycelium was observed on symptomatic tissues, especially flowers. Severely infected flowers and stems eventually rotted, then dried out. Diseased tissue was excised from affected flowers and surfaces and disinfected with 1% sodium hypochlorite, followed by 70% alcohol. The tissue was then rinsed in sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 26°C. Mycelial growth on PDA was initially whitish and turned gray with age. Dark appearing conidiophores bore botryose heads of hyaline, ellipsoid, unicellular conidia, grey in mass, measuring 7.2 (6.2 to 9.5) × 5.3 (4.5 to 6.0) μm. Black, irregular sclerotia formed at random in the culture. These morphological features were typical of those described for Botrytis cinerea (2). The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced (1). BLAST analysis of a 557-bp segment had a 99% similarity with the sequence of Botryotinia fuckeliana (anamorph = B. cinerea). The representative nucleotide sequence has been assigned the GenBank Accession No. KC999986. On the basis of morphological and molecular results, the fungus isolated from diseased konjac flowers and flower tissue was confirmed to be B. cinerea. Pathogenicity tests: Inoculum was prepared from 7-day-old cultures on PDA. Six flowering A. muelleri in 1-liter pots were spray inoculated with a 1.0 × 106 conidia/ml suspension from 7-day-old PDA cultures. As a control, six healthy plants were sprayed with sterile distilled water. Each plant was covered with a transparent polyethylene bag for 3 days and maintained in a greenhouse at temperatures between 20 and 26°C. After 8 days, small, round to irregular brown spots developed on both flowers and stems, which finally blighted. Water-treated plants remained symptomless. Koch's postulates were fulfilled when the pathogen was re-isolated from the diseased organs. Blight on common calla lily (calla lily and Amorphophallus are in the same family, different genera) flower attributed to B. cinerea was previously reported in Argentina (3). To our knowledge, this is the first report of the presence of B. cinerea on A. muelleri in China. References: (1) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (2) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, England, 1971. (3) M. C. Rivera and S. E. Lopez. Plant Dis. 90:970, 2006.