Abstract: The effects of different Fusarium oxysporum strains, which were isolated and purified from alfalfa root rot plants in three different regions of Gansu province, on the growth of alfalfa seedlings were determined. The soil was inoculated with millet-seed inoculum of each isolate before seedlings were transplanted,and then root diseases were scored with root length,shoot height,aboveground biomass and underground biomass being measured after 28 days. Results showed that different strains exhibited significant effect (P<0.05) on root disease severity and growth of alfalfa seedlings,with pathogenicity varying among isolates. After inoculation with different strains,disease index of seedling roots ranged from 46% to 69%;root length and shoot height decreased by 9% to 28% and 20% to 52% respectively;aboveground biomass and underground biomass decreased by 17% to 48% and 15% to 60% respectively. Among these,the strain QY3 had the strongest pathogenicity,followed by QY2,and pathogenicity of the strain LZ3 was the weakest;the strain QY2 resulted in the greatest decrease in root length and aboveground biomass while the strain LT2 decreased greatest in shoot height and underground biomass. This study provides basic theoretical guidance for the control of alfalfa root rot disease.

Key words: Fusarium oxysporum, Alfalfa, Growth, Pathogenicity, Biomass

摘要： 利用从甘肃省3个不同地区紫花苜蓿（Medicago sativa）根腐病植株分离纯化的尖孢镰刀菌（Fusarium oxysporum）菌株，研究了不同菌株对苜蓿幼苗生长的影响。通过不同菌株米粒接种体接种土壤后移栽苜蓿幼苗，28 d后对植株的根部病害进行分级，对株高、根长、地上生物量和地下生物量进行测定。结果表明，不同菌株对苜蓿幼苗根部病害的严重程度和生长有显著影响（P<0.05），致病力强弱存在差异。接种不同菌株后，幼苗根病情指数为46%~69%；根长和株高分别降低9%~28%和20%~52%；地上生物量和地下生物量分别降低17%~48%和15%~60%。其中，菌株QY3致病力最强，其次为QY2，菌株LZ3致病力最弱；菌株QY2导致根长和地上生物量的降低幅度最大；菌株LT2导致株高和地下生物量的降低幅度最大。研究结果为苜蓿根腐病的防治提供了初步的理论指导。

关键词: 尖孢镰刀菌, 苜蓿, 生长, 致病性, 生物量