Abstract:

A new foliar disease on Chinese yam（Dioscorea opposita）was observed in Jiaozuo city，Henan province. The spots with a size ranged from 3–18 mm in diameter show circular and pale to dark brown concentric rings on the leaves. There were black spore masses on older lesions. It was isolated and identified according Koch’s Postulates. The single spore（with a isolation number of 0901）was isolated from the symptomatic portions of the leaves. The pathogenicity test has shown that the pure isolate 0901 was the pathogen causing the disease. Morphological characteristics of 0901 were consistent with the descriptions of Myrothecium roridum. Genomic DNA was extracted from mycelia and which was amplified as a template with the universal primer pair of fungal rDNA ITS1 and ITS4，then the fragment was sequenced. The sequence showed highest identity（99%）to M. roridum. It was concluded that M. roridum was a new pathogen in Chinese yam in Henan province，China. The biological characteristics of the pathogen were tested. The colony spread fastest under 30 ℃，12 h light/dark condition. The pathogen could grow well under pH 5–10，conidia lethal temperature was 52 ℃. The most suitable carbon and nitrogen sources for mycelia growth were lactose and alanine，and the optimum carbon and nitrogen sources were fructose and yeast for spore production.

Key words: Chinese yam, myrothecium leaf spot, Myrothecium roridum