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The potato cyst nematodes ( PCN) Globodera rostochiensis and Globodera pallida are significant pests of potatoes worldwide. The most effective control methods are crop rotation and the deployment of resistant varieties. Complete resistance to G. rostochiensis based on a single resistance gene has successfully been integrated into many varieties. However, resistance to G. pallida has not been as successful to date, with current varieties only exhibiting partial resistance. Combining partially effective quantitative trait loci ( QTLs) for resistance can increase the strength and breadth of the resistance. An additive effect on resistance has previously been demonstrated on combining two QTLs from Solanum tuberosum subsp. andigena ( Gpa IV s adg) and Solanum vernei ( Gpa5). However, populations of G. pallida can be quite divergent and it was unclear whether the relative effects of the individual QTLs and the combined additive effect would be consistent across different G. pallida Pa2/3 populations. Using a mapping population segregating for both QTLs, the effect of the QTLs individually and combined was examined on four UK-derived field populations of G. pallida pathotype Pa2/3, and the relative effects of the individual QTLs and the additive effect of the combination found to be consistent across all populations. [ABSTRACT FROM AUTHOR]

Four field populations of the nematode Globodera pallida were subjected to selection pressure for increased reproductive ability by rearing sub-populations continuously on four partially resistant potato genotypes for 12 generations. The resistance was derived from either Solanum vernei or from S. tuberosum spp. andigena CPC2802. After the 12th generation the original and sub-populations of nematodes were assessed for their reproductive ability on a susceptible genotype and on each of the partially resistant genotypes. Selection pressure was shown to have increased reproductive ability but the increases were specific to the source of resistance used. The average increase on the ex S. vernei clones was from 11% reproduction by the unselected populations to 35·5% reproduction after selection. On the clones derived from CPC2802, which had higher levels of resistance, the increases were larger with an average of 6·6% reproduction for the unselected but 47·4% reproduction after selection. The response to selection differed amongst the initial field populations with some rates of reproduction increased to as much as 79%. A RAPD based analysis of the original and sub-populations after selection indicated small but consistent changes in the genetic structure, which could have been a result of the selection pressure per se and/or the bottlenecks that the populations had gone though. [ABSTRACT FROM AUTHOR]