First Report of a Melanotaenium Species Causing White Mold Disease of Tremella fuciformis in China

Tremella fuciformis is a widely grown edible mushroom in Asia, especially in China for its medicinal and food value (Stamets 2000). In July 2017, white mold infection was observed on T. fuciformis fruiting bodies in a production unit of Youxi, Fujian, China. Approximately 10% of the mushrooms were affected by the mycoparasite and were found not fit for consumption. Initial symptoms appeared as inconspicuous white spots on the surface of T. fuciformis fruiting bodies. The mycoparasite formed a white mass (1 to 3 cm wide and 2 to 4 cm long) within 2 days. Within 5 to 7 days the mycelial mass covered the whole T. fuciformis fruiting body and caused decay. The mycoparasite was collected directly from infected fruiting bodies with sterile needles, inoculated on potato dextrose agar (PDA) and malt extract agar (MEA) plates, and incubated at 23°C. After 5 to 6 days, many cream-white fungal colonies (0.1 to 3.5 mm wide and 1.0 to 6.0 mm long) with limited growth and irregular margins were observed on PDA and MEA plates. Mycelium was aseptate and hyaline. Ballistospores were sessile, hyaline, aseptate, lunate (2.5 to 3.5 µm wide and 8 to 14 µm long), and attached to the side or tip of the hyphae. Teliospores were not present. Morphological characteristics were consistent with those of Melanotaenium endogenum (Ingold 1988). For molecular identification, the internal transcribed spacer (ITS) region and ELF-1α (White et al. 1990; Rehner and Buckley 2005) were amplified and sequenced. A BLAST search in GenBank indicated that amplified ITS sequences of 668 bp (MG806985) had 89 to 88% similarity to Melanotaenium species sequences (DQ789981, DQ875347, and JN367289) and ELF-1α sequences of 497 bp (MH327256) had 92% similarity to Melanotaenium euphorbiae (JN367365). For inoculum production, mycelial discs were aseptically transferred into potato dextrose broth (PDB) and incubated in dark at 23°C with continuous shaking at 150 rpm for 7 to 10 days. Mycelium was separated from PDB by filtration, and the ballistospore suspension (1 × 10⁷ conidia/ml of sterile water) was prepared with filtrate for inoculation. Each fruiting body of T. fuciformis (30 biological replicates in total) was sprayed with the ballistospore suspension, and sterile distilled water served as a control. Inoculated fruiting bodies and controls were maintained at 23°C and 95% relative humidity. White colonies of the mycoparasite developed on T. fuciformis fruiting bodies 2 days after inoculation. The symptoms were similar to those of the original diseased fruiting bodies, and the controls remained asymptomatic. The mycoparasite was reisolated from the infected fruiting bodies and identified as Melanotaenium sp. based on morphological and molecular analysis. To our knowledge, this is the first report of Melanotaenium sp., causing white mold disease on T. fuciformis worldwide. T. fuciformis is one of the most popular fungi in the cuisine and medicine of China, and the presence of Melanotaenium infection is of great concern to producers of T. fuciformis.