Interaction between root-knot nematodes and Solanum spp. : variation in pathogenicity, cytology, proteins and DNA = [De interactie tussen wortelknobbelnematoden en Solanum spp. : variatie in ziekteverwekkend vermogen, cytologie, eiwitten en DNA]

This thesis describes genetic variation in the root-knot nematodes Meloidogyne hapla, M. chitwoodi and M. fallax, particularly with respect to their pathogenicity on Solanum spp. Significant differences in virulence and aggressiveness were shown to exist between and within these species. Evidence for the occurrence of pathotypes of M. chitwoodi on S. bulbocastanum was obtained. Differences in virulence corresponded to differences in overall genetic variation, revealed by 2-D protein electrophoresis. A distinct species classification for Meloidogyne spp. was obtained by AFLPs and 2-D electrophoresis. In mating experiments M.chitwoodi and M. fallax appeared to be true biological species as testified by infertility of their hybrids. Abnormalities during meiosis in oocytes of an isolate of M. hapla and in spermatocytes of isolates of M. fallax resulted in limited sexual recombination. The combination of post-reductional meiosis and the fusion of the second polar body with the egg pronucleus is probably responsable for maintenance of heterozygosity in meiotic parthenogenetic Meloidogyne. The constant production of males in these populations makes the development of homogeneous isolates impossible. A method was described to conserve nematode germplasm by long-term preservation of juveniles in liquid nitrogen.