Two allopolyploid ascomycete fungal plant pathogens were not rescued by vertical transmission

As noted at the beginning of this letter, Selosse & Schardl (2007) have proposed a convincing model to explain the initial success of allopolyploid hybrid grass endophytes, based on a switch to vertical transmission and the development of new host specificities. Two examples of allopolyploid plant pathogens are known. New host specificity may be sufficient to explain the existence of the hybrid Verticillium isolates in cruciferous hosts, but neither hybrid has switched to primarily vertical transmission and to date we have seen no explanation for the success of B. allii on onions. In conclusion, the evidence suggests that their model cannot be applied directly to the currently known plant pathogenic allopolyploid hybrids.