Molecular genetic investigations and reclassification of Fusarium species in sections Fusarium and Roseum

The genetic relationships of 56 isolates from the taxa traditionally grouped in Fusarium sections Fusarium (syn. Discolor) and Roseum were studied using the Restriction Fragment Length Polymorphism (RFLP) technique, by Southern hybridisation with random genomic and mitochondrial DNA probes originating from Fusarium species. Pairwise distances between taxa were calculated from the 957 RFLP bands scored on autoradiograms, using Dice's coefficient in the RAPDistance computer program. A strong genetic relationship was observed between F. graminearum, F. culmorum and F. crookwellense. However, the morphologically similar taxon, F. pseudograminearum shared only approximately 40% of genomic DNA RFLP bands with these taxa, demonstrating affinity, but less direct genetic similarity. Of all taxa examined F. pseudograminearum and F. graminearum shared the greatest similarity in mitochondrial DNA RFLP patterns. F. avenaceum subsp. avenaceum, subsp. aywerte and subsp. nurragi displayed very little genetic resemblance with each other, or with F. heterosporum and the cereal infecting pathogens. F. torulosum was closest genetically to subsp, avenaceum, with approximately 22% of genomic DNA RFLP bands in common. On the basis of these results F. avenaceum subsp. aywerte and subsp. nurragi are elevated to species rank, as F. aywerte comb., nov. and F. nurragi comb. nov., and F. avenaceum subsp. avenaceum is returned to its former species status.