Study on identification of cucumber seedborne Fusarium species and testing of their pathogenicity

In order to study the seedborne Fusarium species and their harmness of cucumber seeds of popularly planted varieties,cucumber seeds of twenty-one varieties from cucumber-growing regions in China were collected for Fusarium detection.Nine Fusarium isolates were isolated from seed embryos and seed surface.The isolates were identified using morphology and DNA sequencing analysis.Effects on seed germination and pathogenicity of these Fusarium isolates were determined.Results showed that the nine Fusarium isolates belong to three species,i.e.Fusarium oxysporum(4 isolates),F.moniliforme(4 isolates) and F.prolifertum(1 isolate).The four F.oxysporum isolates had significant effect on seed germination,compared to the control treatment.The values of the germination index,the seedling vigor index,root length and fresh weight of seedlings decreased significantly in the treatment of F.oxysporum.Results also showed that the isolates of F.oxysporum were pathogenic to seedlings of cucumber and caused typical wilt symptoms on leaves,fulfilling Koch's postulates.All the other five isolates of Fusarium had suppressive effect on seed germination of cucumber,but they were not pathogenic to cucumber seedlings.To our knowledge,this is the first report of the seedborne F.oxysporum pathogenic to cucumber seedlings in China.