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

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...