Because differing opinions have been expressed concerning the taxonomic status of Nacobbus aberrans, experiments based on crossing combinations of different N. aberrans populations were undertaken. Five (N1 to N5) South American populations differing in their host preference (N1, N2, N3 able to infect potato and sugarbeet; N4, N5 able to infect sugarbeet, but not potato) were reciprocally crossed. Three populations assigned to different race groups, N1 (Bolivia, potato group), N2 (Peru, potato group) and N4 (Peru, sugar beet group) were readily able to cross between each other and to give fertile and viable progeny, regardless of their geographical origin, race group and for most of the crossing combination ([female] × [male]). When crossing a sugar beet population (unable to develop on potato) as female with a male from a potato population, the progeny was able to develop on potato. The N5 population, which belongs to the sugarbeet group from Argentina, was able to cross with other populations, but the progenies obtained were always infertile and nonviable. This population should be considered as a separate species. These findings provide evidence that the N. aberrans complex in South America comprises at least two species.
