Adjunct Assistant Professor Iowa State University Ames, Iowa, United States
Abstract Text: Fusarium graminearum (Fg) causes seedling disease and root rot in soybean, often in fields that also show symptoms of iron-deficiency chlorosis. These two stresses may interact in complex ways. Microorganisms such as Fg can secrete iron-chelating compounds (siderophores) that may contribute to pathogen fitness and pathogenicity. In F. graminearum, nps genes are known to control siderophore synthesis and secretion. In this study, soybean seeds were inoculated with a wild-type Fg strain and several mutants with one or more deletions in nps genes. Inoculated soybeans, Clark (iron efficient) and Isoclark (iron inefficient) were assessed in rolled-towel assays and in a DTPA nutrient-buffered hydroponics system containing iron sufficient (100 µM Fe (NO3)3) and iron-limiting conditions. Growth parameters, iron deficiency chlorosis (IDC), disease severity index (DSI) and chlorophyll content were evaluated. Detailed root morphological and architectural measurements were analyzed by WinRHIZO root-scanning software. Statistical data analysis was performed by R. For both Clark and Isoclark, inoculation with the triple mutant nps1nps2nps3 strain had smaller effects on IDC and DSI, fresh plant weight, and root volume than inoculation with the WT strains. In general, for Clark, similar responses were observed when challenged by the triple mutant or nps6 strains. Phenotypic preliminary results show that the triple mutant nps1nps2nps3 strain lacking three genes associated with key siderophore synthesis may have reduced virulence in soybeans.
