00340nas a2200121   4500008004100000022001400041245002800055210002800083300001200111490000800123100001700131856007000148       1992                        eng d  a0028-083600aOak mortality in Iberia0 aOak mortality in Iberia  a539-5390 v3601 aBrasier, C M  uhttp://www.nature.com/nature/journal/v360/n6404/abs/360539a0.html01900nas a2200145   4500008004100000245007800041210006900119300001400188490000700202520144300209100001701652700001701669700001601686856005201702       1999                        eng d00aOrigin of a new Phytophthora pathogen through interspecific hybridization0 aOrigin of a new Phytophthora pathogen through interspecific hybr  a5878-58830 v963 aPlant disease epidemics resulting from introductions of exotic fungal plant pathogens are a well known phenomenon. An associated risk that accelerated pathogen evolution may be occurring as a consequence of genetic exchange between introduced, or introduced and resident, fungal pathogens is largely unrecognized. This is, in part, because examples of natural, interspecific hybridization in fungi are very rare. Potential evolutionary developments range from the acquisition of new host specificities to emergence of entirely new pathogen taxa. We present evidence from cytological behavior, additive nucleotide bases in repetitive internal transcribed spacer regions of the rRNA-encoding DNA (rDNA), and amplified fragment length polymorphisms of total DNA that a new, aggressive Phytophthora pathogen of alder trees in Europe comprises a range of heteroploid-interspecific hybrids involving a Phytophthora cambivora-like species and an unknown taxon similar to Phytophthora fragariae. The hybrids marked developmental instabilities, unusual morphological variability, and evidence for recombination in their internal transcribed spacer profiles indicates that they are of recent origin and that their evolution is continuing. The likelihood of such evolutionary events may be increasing as world trade in plants intensifies. However, routine diagnostic procedures currently in use are insufficiently sensitive to allow their detection.1 aBrasier, C M1 aCooke, D E L1 aDuncan, J M  uhttp://www.pnas.org/content/96/10/5878.abstract