Background: Fusarium pseudograminearum is the predomenant causal agent of devastating crown rot diseases in cereal crops around the world. Mycoviruses have attracted increasing attention as potential biological control agents on plant diseases. The unique mycoviruse isolated from F. pseudograminearum is Fusarium pseudograminearum megabirnavirus 1 (FpgMBV1), which is a new member of the family Megabirnaviridae. To determine the hypovirulence effects of FpgMBV1 on F. pseudograminearum to wheat plants is critical for the potential application of FpgMBV1 in the control of cereal crown rot disease.
Methods: Hyphal tip cultures were conducted to obtain a FpgMBV1-free strain, named as FC136-2A-V－. A hyg gene was transformed into a highly virulent virus-negative stain WZ-8A of F. pseudograminearum to obtain the deduced strain WZ-8A-HygR-V－. WZ-8A-HygR-V－ was used in pairing culture with the FpgMBV1-carrying F. pseudograminearum strain FC136-2A to obtain a FpgMBV1-positive strain WZ-8A-HygR-V+. Then the two pairs of strains, FC136-2A-V－/FC136-2A and WZ-8A-HygR-V－/WZ-8A-HygR-V+, were used to determine the potential effect on F. pseudograminearum by the infection of FpgMBV1 through tests on the growth, sensitivity to stress and cellophane penetrating ability in vitro and the pathogenicity to wheat plants.
Results: FpgMBV1 could be cured by hyphal tip culture and horizontally transferred between F. pseudograminearum strains through pairing culture. Reduction of FpgMBV1-carrying strains on hyphal growth were found under the treatment of 0.5% SDS. No differences in the growth rates of tested strains in the treatments with 1 M NaCl, 1 M KCl, or 15 mM H2O2. Comparing to virus-negative strains, the In vitro cellophane penetrating ability was lost in FpgMBV1-carrying strains. The disease index of wheat plants inoculated with FC136-2A-V- was significantly higher than that inoculated with FC136-2A, while the pathogenicity of WZ-8A-HygR-V+ reduced significantly comparing to that of WZ-8A-HygR-V－.
Conclusions: FpgMBV1 is the causal agent of the low pathogenicity to wheat plants of its original host F. pseudograminearum strain FC136-2A. And FpgMBV1 could be horizontally transferred to another F. pseudograminearum strain and reduce its pathogenicity to wheat plants.