First report of corn kernel brown spot disease caused by Mucor irregularis in China.
In October 2012, a brown spot disease was found on maize kernels during a field survey in Nanyang city, Henan, China. The incidences of affected ears and kernels were 2 to 10% (n=600) and 0.08 to 0.4% (n=25 000), respectively. Symptoms first appeared as circular or irregular brown spots on the endosperm. These spots subsequently enlarged or coalesced, resulting in the formation of a large light-brown or light-yellow irregular speckle commonly surrounded by a dark-brown edge. Based on morphological characteristics, molecular investigations (sequence analysis of the rDNA internal transcribed spacer region and D1/D2 region of the nuclear large subunit ribosomal RNA gene) and pathogenicity tests, the causal agent was identified as M. irregularis. This fungus was reported as a pathogen causing human skin diseases in China, America and India, and as a phytopathogen causing fruit rot on durian. This is thought to be the first report of M. irregularis causing maize kernel brown spot disease in China.