Genetic diversity of Xiphinema pachtaicum and Xiphinema index populationsbased on mitochondrial and nuclear DNA variation

Abstract: The dagger nematodes Xiphinema pachtaicum and X. index are one of the mostwidespread and frequently occurring Xiphinema species co-infesting vineyards and other cropsand natural habitats worldwide. The prevalence of X. pachtaicum and the importance of X. indexas a virus-vector, together with the possibility of the latter being an introduced species andoccupying a more restricted habitat than X. pachtaicum make them interesting nematodes for thestudy of population genetics. The primary objective of this study was to determine the geneticstructure of X. pachtaicum and X. index populations using nine and seven populations,respectively, from different “wine of denomination of origin (D.O.) zones” in Spain and Sardinia(Italy), by the study of the mitochondrial (cytochrome oxidase c subunit 1 or COI) and nuclear(D2-D3 expansion segments of 28S rDNA) markers. Both Xiphinema species showed low intraspecificdivergence among COI sequences, ranging from 0.2% (1 base substitution) to 2.3% (10substitutions) in X. pachtaicum, and from 0.2% (1 base substitution) to 0.4% (2 substitutions) inX. index. Population genetic structure with a significant variation among populations within D.O.zones and within populations were found for both species. Nevertheless, molecular differencesamong grapevine-growing areas were not significant. It is hypothesized that this genetic structuremay have been originated by extensive and continuous grapevine cultivation in the sampledgeographic areas, as well as inadequate sanitation practices during long periods. Results alsodemonstrated that the two DNA regions studied are suitable diagnostic markers for X. index andX. pachtaicum.