Some aspects of resistance to and tolerance of potato cyst nematodes in potato = Enkele aspecten van resistentie tegen en tolerantie van aardappelcysteaaltjes in aardappel

Potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida , are major pests of the potato. In this thesis, research on some aspects of resistance to and tolerance of PCN is presented. The distinction of virulence groups with a hierarchical clustering procedure is proposed as an alternative for the currently distinguished pathotypes. Resistance in potato cultivars should be expressed in a quantitative way, tested against PCN populations representative of virulence groups. A previously unknown major gene for resistance to some G. pallida populations was found, thought to be derived from S.tuberosum ssp. andigena CPC 1673. Several potato cultivars appeared to carry this gene, presumably due to linkage of this gene with a trait they have been selected for. Several genotypes with G. pallida resistance from S. vernei , as currently used in potato breeding, appeared to be highly intolerant to G. pallida . Differences in tolerance between G. pallida resistant genotypes in the field were associated with differences in biomass of infested plants in the greenhouse, relatively early in growth. In progenies of crosses, tolerance and resistance appeared not to be related. Selection for tolerance in a G. pallida resistance breeding programme is advised, in order to avoid the development of resistant, but highly intolerant potato cultivars. Multiple regression analysis revealed that the tolerance of the tested genotypes was associated with the induced rate of hatching and the capacity of root growth after infection.