Abstract: In order to identify the pathogen causing alfalfa Fusarium root rot in Shunyi District of Beijing,the pathogen was isolated and purified from diseased samples using conventional tissue separation method. Combined with morphological characteristics,pathogen was identified by phylogenetic tree constructed by multi-gene sequence analysis(rDNA-ITS,EF-1α and RPB2). According to Koch’s Postulates,the pathogenicity of different pathogens was analyzed. Moreover,the mycelial growth rate method was further used to determine the biological characteristics of strongly pathogenic Fusarium and the inhibitory effect of fungicides. The results showed that the total of 26 strains were obtained from afalfa samples. 7 of them were identified as potential pathogens of afalfa Fusarium root rot,and all are Fusarium species,respectively belonging to F. ipomoeae,F. compactum and F. flagelliforme in the Fusarium incarnatum-equiseti species complex (FIESC),as well as to F. acuminatum and F. solani. Among them,MsF1(F. ipomoeae)had the highest pathogenicity,and the disease index of inoculated alfalfa seedlings was 64.33. The biological determination showed that MsF1 was most suitable for growth under the conditions of temperature 30℃,pH 6~10 and low nitrogen. MsF1 could tolerate the stress of NaCl at 150 g·L^-1,and the inhibitory effect of iprodione was not significant,with less than 10 percent inhibition at the concentrations tested,while the EC₅₀ value of fludioxonil was 0.142 μg·mL^-1. In this study,it was reported for the first time that FIESC could infect alfalfa and cause Fusarium root rot,which provided scientific basis and theory support for the diversity study and effective field control of alfalfa root rot.

Key words: Alfalfa, Fusarium root rot, Isolation and identification, Pathogenicity, FIESC

摘要： 为明确北京市顺义区苜蓿(Medicago sativa L.)镰刀菌根腐病的病原菌种类，本研究采用常规组织分离法对发病苜蓿样品进行病原菌分离纯化；利用形态学特征观察结合多基因序列分析(rDNA-ITS，EF-1α和RPB2)的系统发育树对病原菌进行鉴定，并按照柯赫法则测定菌株致病性；采用菌丝生长速率法，测定强致病镰刀菌的生物学特性及杀菌剂的抑制作用。结果表明，本研究共分离获得26株菌株，7株鉴定为镰刀菌，分别属于Fusarium incarnatum-equiseti species complex(FIESC)中的F. ipomoeae,F. compactum和F. flagelliforme以及锐顶镰刀菌F. acuminatum和腐皮镰刀菌F. solani，其中MsF1(F. ipomoeae)的致病力最强，接种苜蓿幼苗发病的病情指数为64.33。生物学特性测定表明，MsF1在温度30℃、pH值为6~10、低氮条件下最适合生长，可耐受150 g·L^-1的NaCl胁迫；异菌脲对其抑制效果不明显，供试浓度下抑制率低于10%，而咯菌腈对其半数效应浓度(Median effect concentration,EC₅₀)为0.142 μg·mL^-1。本研究首次报道FIESC可侵染紫花苜蓿引起镰刀菌根腐病，为苜蓿根腐病的多样性研究和田间有效防治提供科学依据和理论支撑。

关键词: 苜蓿, 镰刀菌根腐病, 分离鉴定, 致病性, FIESC