Obligatory amphimixis and variation in chromosome number within and among South American populations of Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944 (Nematoda&COLFAML; Pratylenchidae)

There are conflicting opinions concerning the reproductive mode and the taxonomic status of Nacobbus aberrans, so we have addressed these issues by an experimental approach based on the inoculation of immature and vermiform females in in vitro conditions. Complementary information on chromosome number was provided. Five South American populations of Nacobbus aberrans were tested. No population was observed to be able to reproduce by parthenogenesis in in vitro conditions. The basic haploid chromosome number seems to be seven, at least for four of the five populations studied. However, all populations had individuals with haploid chromosome numbers ranging from five to eight, six to eight being the most frequent number, regardless of the 'race' group or the native country. The variation in the chromosome number suggests that N. aberrans may be considered as a set of different karyological genetic entities.