Isolation and identification of the pathogens causing root rot disease of Medicago sativa

Fifteen samples of root rot disease of Medicago sativa were collected from Zhangye and Jiuquang of Gansu,China.Pathogenicity of fungal isolates obtained from these samples was tested by verifial standard means of the Koch's Postulation.The results showed that the isolates mainly belonged to Fusarium spp.Infection analysis indicated that F.solani had the strongest virulence with a disease seedlings rate of more than 60%,whereas pathogenicity rate of F.oxysporum,F.moniliforme ranged from 16.7% to 23.3%.When F.solani was co-inoculated with other isolates,the disease indices of mixed inoculations were all higher than those of their individual infection.The combined inoculations of F.solani with F.oxysporum,or F.moniliforme induced higher rates of disease seedlings than those of F.solani with other fungi.Our results revealed that F.solani was the major pathogen of root rot disease of Medicago sativa,whereas Fusarini sajani and F.moniliforme,F.oxysporum and the other two Fusarium species only played an accessory role in Medicago sativa.