Identification of mitochondrial markers for genetic traceability of European wild boars and Iberian and Duroc pigs

Iberian pigs and wild boars are the source of highly priced meat and dry-cured products. Iberian maternal origin is mandatory for labeled Iberian products, making necessary the authentication of their maternal breed origin. Discrimination between wild and domestic pig maternal origin may be useful to distinguish labeled wild boar meat obtained from hunting or farming. In order to detect useful polymorphisms to trace Iberian, Duroc and wild boar maternal lineages, we herein investigated the complete porcine mitochondrial DNA (mtDNA) using three complementary approaches. Near-complete mtDNA sequences (16989 bp), excluding the minisatellite present in the displacement loop region (D-loop), were successfully determined in six Iberian pigs, two Duroc and six European wild boars. To complete the mtDNA analysis, the D-loop minisatellite region was also analyzed in the same set of samples by amplification and capillary electrophoresis detection. Finally, the frequencies of Asian and European Cytochrome B (Cyt B) haplotypes were estimated in Iberian (n = 96) and Duroc (n = 125) breeds. Comparison of near-complete mtDNA sequences revealed a total of 57 substitutions and two Indels. Out of them, 32 polymorphisms were potential Iberian markers, 10 potential Duroc markers and 16 potential wild boar markers. Fourteen potential markers (five Iberian and nine Duroc), were selected to be genotyped in 96 Iberian and 91 Duroc samples. Five wild boar potential markers were selected and tested in samples of wild boars (73) and domestic pigs including: 96 Iberian, 16 Duroc, 16 Large White and 16 Landrace. Genotyping results showed three linked markers (m.7998C>T, m.9111T>C, m.14719A>G) absent in Duroc and present in Iberian pigs with a frequency 0.72. Six markers (m.8158C>T, m.8297T>C, m.9230G>A, m.11859A>G, m.13955T>C, m.16933T>C), three of them linked, were absent in Iberian pigs and present in Duroc with a joint frequency of almost 0.50. Finally three linked markers (m.7188G>A, m.9224T>C, m.15823A>G) were solely detected in wild boars with a frequency 0.22. The D-loop minisatellite results showed overlapping ranges of fragment sizes and suggested heteroplasmy, a result that nullify the use of this region for the development of breed diagnostic markers. The Cyt B haplotype results showed the presence of European haplotypes in Iberian while one of the Asian haplotypes was detected in Duroc with a frequency 0.22, linked to the Duroc marker m.9230G>A. Our results are valuable to resolve the problems of Iberian and wild boar maternal origin determination but additional markers are required to achieve totally useful genetic tests.