Abstract
Although the use of natural resistance is the most effective management approach against the potato cyst nematode (PCN) Globodera pallida, the existence of pathotypes with different virulence characteristics constitutes a constraint towards this goal. Two resistance sources, GpaV (from Solanum vernei) and H3 from S. tuberosum ssp. andigena CPC2802 (from the Commonwealth Potato Collection) are widely used in potato breeding programmes in European potato industry. However, the use of resistant cultivars may drive strong selection towards virulence, which allows the increase in frequency of virulent alleles in the population and therefore, the emergence of highly virulent nematode lineages. This study aimed to identify Avirulence (Avr) genes in G. pallida populations selected for virulence on the above resistance sources, and the genomic impact of selection processes on the nematode. The selection drive in the populations was found to be specific to their genetic background. At the genomic level, 11 genes were found that represent candidate Avr genes. Most of the variant calls determining selection were associated with H3-selected populations, while many of them seem to be organised in genomic islands facilitating selection evolution. These phenotypic and genomic findings combined with histological studies performed revealed potential mechanisms underlying selection in G. pallida.
Highlights
Pests and pathogens of plants can engage in complex relationships with their hosts to establish conditions to enable survival and reproduction, whereas plants invest energy in their defence strategiesGenes 2020, 11, 1429; doi:10.3390/genes11121429 www.mdpi.com/journal/genesGenes 2020, 11, 1429 to counteract them
The G. pallida populations from The James Hutton Institute potato cyst nematode (PCN) collection used were Lindley, Newton and two sub-populations generated by selection on partially resistant germplasm (n-11305 and n-11415)
In order to confirm that H3-mediated resistance is based on a typical R gene response rather than a general toxicity to invading nematodes, the histology and ultrastructure of the interaction were compared between G. pallida and the susceptible S. tuberosum cv
Summary
Genes 2020, 11, 1429 to counteract them During these interactions, pathogen-derived effectors promote virulence by suppressing or evading activated host defence responses. An effector recognised as part of a resistance response is termed an avirulence (avr) factor, and their interaction with the cognate R gene product is usually highly specific [2,3,4]. These interactions have been summarised as part of the zig zag model [2]. It has been estimated that 9% of global potato production is lost annually to these two species [5]. The degree of resistance they confer can vary and may diminish during the successive crosses that are performed to produce commercially attractive cultivars
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