Needle mushroom (Flammulina velutipes) is an edible and medicinal mushroom with annual production yields for China exceeding 2 million metric tons. Hebei province is one of the biggest producers of needle mushrooms in China. From 2009 to 2010, red rust-colored sporulation (fungal mycelia and conidia) was found on the substrate surface of white needle mushroom bags in more than 10 mushroom cultivation operations in Hebei. The rust-colored sporulation covered the substrate surface, where the development of the fruiting bodies was inhibited; the stipes were sparse and became light brown when the substrate was slightly affected. The fruiting bodies on severely affected substrate were unable to complete development or shriveled and died off on the substrate. More than 30 to 40% substrate bags were contaminated with the red rust mold, with approximately a 40% yield reduction in each production house. Single conidia were isolated from the red rust mold and cultured on potato dextrose agar at 25°C in the dark. The colony was round, compact, reddish-brown, and slow-growing (2 to 3 mm/d). Main conidiophore axes were erect, often branched in five to seven layers, tapered from the base to the upper part, pale reddish brown at the base, and almost hyaline at the apex. Two to five phialides usually verticillated at each level along the main stipe and its branches. Phialides were narrowly flask-shaped and only very slightly swollen at the base. Conidia were oval, measured 3.5 to 5.4 (4.5) × 2.3 to 3.6 (3.0) μm, L/W = 1.2 to 2.0 (1.5), and formed pale reddish brown, slimy heads. The isolate was tentatively identified as Acrostalagmus luteo-albus based on its morphological characteristics (2). For molecular analysis, the internal transcribed spacer (ITS) regions of ribosomal DNA from the isolate were PCR-amplified using universal primers ITS1 and ITS4. The resulting sequence (Accession No. KC127681) submitted to GenBank had a 99% identity to that of A. luteo-albus (JN545827) isolated from vineyard soil and Accession No. JQ387575 isolated from twig of declining persimmon tree. To confirm the pathogenicity of the isolate to needle mushroom, five bags of needle mushroom with stipes of 1 to 2 cm long were inoculated with a conidia suspension (105 conidia/ml) of the isolate and incubated at 13 to 15°C in the dark, while five non-inoculated bags (sprayed with sterile water only) were used as a control. Five days after inoculation, the development of the fruiting body was obviously inhibited, and a few growing fruiting bodies became light brown, compared with the non-inoculated fruiting bodies, which were growing healthily and fast and were white with no symptoms. The pathogen was re-isolated from the inoculated fruiting bodies. A. luteo-albus is primarily saprophytic but is sometimes pathogenic. Indeed, it has been associated with post-harvest rot of ginger rhizomes in Brazil (1). To our knowledge, this is the first report of A. luteo-albus causing damage to needle mushroom in China.
References: (1) S. I. Moreira et al. Trop. Plant Pathol. 38:218, 2013. (2) R. Zare et al. Mycol. Res. 108:576, 2004.