Exploring and exploiting the resistance to Globodera pallida in potato

Abstract

The potato cyst nematodes (PCN) Globodera pallida and G. rostochiensis are economically important potato pests in almost all regions where potato is grown. Studying the composition, distribution and virulence of PCN populations in fields, and finding new sources of naturally occurring resistance in wild potato species is important for the management of these pests. In Scotland, up to three different introductions of G. pallida, determined by mitotyping, were found to be present in fields. To investigate whether cysts in a population show a correlation between mitotype and different virulence levels, “single cyst” lines were generated, mitotyped, and their virulence to different potato cultivars was determined. One mitotype was shown to correlate with G. pallida pathotype Pa3, but overall, the mitotypes are not usable as reliable virulence markers. A phylogenetic analysis was performed to determine the relationships between British G. pallida populations. In addition, single nucleotide polymorphisms (SNPs) in genomic DNA were identified that represent candidate virulence markers. A screen of wild potato germplasm was undertaken to identify new resistance against G. pallida. The diploid species Solanum spegazzinii Bitter accession 7195 shows resistance to G. pallida pathotypes Pa1 and Pa2/3. A cross and first backcross of S. spegazzinii with S. tuberosum group Phureja cultivar Mayan Gold was performed, and the level of resistance to G. pallida Pa2/3 was determined in progeny. Bulked-segregant analysis sing generic mapping enrichment sequencing and genotyping-by-sequencing was performed to identify SNPs that are genetically linked to the resistance, using S. tuberosum group Phureja clone DM1-3 516 R44 as a reference genome. These SNPs were converted into allele specific PCR assays, and the resistance was mapped using graphical genotyping. The resistance was successfully introgressed into a tetraploid potato cultivar by a tetraploid-diploid interploidy cross.