They found that the severe kind may have formed from a recombination of less harmful grass viruses.In the process of recombination, the parent viruses exchanged a gene.

• 他们发现，危害较大的这种病菌成型于多种具有较小危害的草菌的合并，而且，在合并过程中，现在形成这种病菌改变了机质。