Abstract: In order to clarify the pathogen and biological characteristics of alfalfa leaf blight in Yangling District and to provide a theoretical basis for the diagnosis and control of the disease in the field,the isolation,purification,molecular identification,leaf isolation and in vivo pathogenicity test of pathogen of medicago leaf blight collected from Yangling District of Shanxi Province were performed in this project,and the pathogen was eventually identified as Rhizoctonia solani. The result of biological characteristics showed that the optimum pH for its growth was 7. Dark condition is beneficial for the growth of Rhizoctonia solani. Besides,soluble starch,not fructose was the optimal carbon source for mycelia growth of this pathogen. The optimal nitrogen source was potassium nitrate instead of ammonium nitrate.

Key words: Medicago sativa, leaf blight, Rhizoctonia solani, biological characteristics

摘要： 为明确杨凌区紫花苜蓿叶枯病病原菌种类及其生物学特性，为该病害在生产中的诊断及防治提供理论依据，本研究对采自陕西省杨凌区苜蓿叶枯病病样进行致病菌分离、纯化、分子鉴定、离体叶片及活体致病性测定，确定了引起陕西省杨凌区苜蓿叶枯病的病原菌为立枯丝核菌（Rhizoctonia solani）。对苜蓿叶枯病原菌生物学特性研究发现该菌最适pH值为7；黑暗条件下有利于该菌生长；可溶性淀粉是其较好的碳源，而对果糖利用效果最差；最适氮源为硝酸钾，而对硝酸铵利用效果最差。

关键词: 紫花苜蓿, 叶枯病, 立枯丝核菌, 生物学特性