Pathotype-specificity in potato cyst nematodes, a reconsideration

Abstract

Within the two potato cyst nematode (PCN) species, Globodera rostochiensis and G.. pallida, eight pathotypes are presently discerned by seven differential Solanum clones, whereby resistance is defined as a Pf/Pi ratio < 1 .0, and susceptibility as a ratio above 1 .0 . This pathotyping is felt to be unsatisfactory . Reconsidering the original data and data published by others resulted in the conclusion that there are only three reliably recognizable Ro-pathotypes Rol/Ro4, Ro2/Ro3 and Ro5 . The differential clones 60 .21 .19 and, 65 .346 .19 differentiate only between the two species . Within G. pallida it does not seem possible to identify pathotypes reliably . The resistance-virulence pattern is of a quantitative nature fitting a polygenic system . There appear to be pathotype-specific, effects, which are not large enough to identify and classify pathotypes reliably . It is therefore suggested to rename the Ro-pathotypes into Rol (old Rol and Ro4), Ro3 (old Ro2 and Ro3) and Ro5 (old Ro5) and to speak of more and less virulent Pa-populations .The rigorous requirements for resistance in various countries present great problems to the breeders and result in the removal of much valuable partial resistance . Especially with G. pallida these rigorous requirements are probably an obstacle rather than an encouragement to solve the pallida problem .

Assessment of the use of high-performance capillary gel electrophoresis to differentiate isolates of Globodera spp.

“…The population bottlenecks have generated a continuous range of quantitative variation in all allele frequencies. Our results confirm that there are no groups of isolates greatly different from one another, and that the protein profiles we obtained are not related to groups with distinct characteristics, namely the virulence groups or pathotypes as defined by Kort et al (1977), EPPO (1985), Nijboer and Parlevliet (1990) and Phillips and Trudgill (1998).…”

“…The analysis of the results assigned pathotypes Ro1 and Ro4 to different clusters and suggested that there is more proximity between pathotypes Ro1 and Ro5, and Ro2 and Ro4. In a similar way, Pa1 was placed close to Pa2 but both were quite far from Pa3, while in studies conducted in Europe, Pa2 was closer to Pa3 (EPPO, 1985;Nijboer & Parlevliet, 1990;Phillips & Trudgill, 1998). The Portuguese isolates fell into two main groups: i) all G. pallida isolates were grouped with 16 G. rostochiensis isolates, with two of the G. pallida isolates (PT104 and PT116) clustered together and the other (PT5701) within the G. rostochiensis isolates; and ii) the other G. rostochiensis isolates together with the eight 'pathotype' isolates (Fig.…”

“…Inter-and intra-specific variability of potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida, has been evaluated using the reaction of different potato genotypes with quantitative resistance, following several pathotype schemes (Canto Saenz & De Scurrah, 1977;Kort et al, 1977;Nijboer & Parlevliet, 1990). However, there has been much debate about their value and several studies have indicated that differences between pathotypes are unclear (Phillips & Trudgill, 1985;Trudgill, 1985;Mugniéry et al, 1989).…”

RNA interference in Pratylenchus coffeae: Knock down of Pc-pat-10 and Pc-unc-87 impedes migration

“…Host resistance can either be naturally present in the crop or be introgressed from wild relatives through conventional breeding methods, or be engineered through plant transformation. Natural resistance by breeding approaches have been successful only in few crops due to the limited range of resistance and breaking down of resistance by virulent populations [4].…”

Variation in resistance level of potato genotypes and virulence level of potato cyst nematode populations

“…The above mentioned concept of pathotypes and the classification of PCN resistance has been criticized on a number of points (Trudgill, 1985 ;Nijboer & Parlevliet, 1990) . First, for the identification of pathotypes homogeneity of virulence is required (Parlevliet, 1985), while the pathotype concept of Kort et al .…”