Virulence of Canarian Populations of Potato Cyst Nematodes (Globodera Spp.)

The virulence spectrum of the potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis, from the Island of Tenerife was assessed and compared with that found in Europe. Within the G. rostochiensis populations, all the Canarian populations, with the exception of one (R2), were avirulent to the H1 resistance gene and therefore belong to the virulence group Ro1/Ro4. Within the G. pallida populations from Tenerife it was apparent that the virulence gene which overcomes the H2 resistance gene is present only at a low frequency. Four populations, P4, P7, P8 and P13, would be classified as pathotype Pa1. A wide range of variation in virulence against clones derived from S. vernei was observed, indicating a continuum of virulence, rather than discrete pathotypes. There was some correlation between the fitness of the populations on the hosts derived from S. vernei and those with no resistance, but less correlation between virulence on the ex-S. vernei clones and one derived from ex-S. tuberosum ssp. andigena CPC 2802. The reproduction of the G. pallida populations on three ex-S. vernei clones also indicated that increasing resistance is predominantly additive and that the nature of virulence towards the three ex-S. vernei clones tested is similar. The differences in the multiplication of the populations on a particular clone may reflect the number of resistance genes present in the clone. A clone derived from ex-S. tuberosum ssp. andigena CPC 2802 was comparatively uniformly resistant to all the populations. Its resistance appears to be different from that in the ex-S. vernei clones and to interact with at least in part, different genes in G. pallida for virulence. The nature of resistance in the different clones tested and aspects concerning the epidemiology of potato cyst nematodes are discussed.