ntegrative approach and molecular barcoding of dagger and needle nematodes infesting grapevine soils in Portugal

Abstract

Dagger (Xiphinema spp.) and needle (Longidorus spp., Paralongidorus spp.) nematodes are two of the main groups of parasitic nematodes in grapevines worldwide, causing severe damage to plants by their direct feeding; in addition, some species may transmit plant viruses. Some of these nematode species are included in the list of quarantine organisms in many countries. Grapevine fanleaf virus (GFLV) is specifically transmitted by Xiphinema index, and it is one of the most harmful viruses to vineyards wordwide. Despite their phytopathological importance, this research area has been deserted for over fifteen years in Portugal. In recent years, plant health of the Portuguese vineyards has declined, characterized mainly by reduced vigor in plants. Thus, the main objective is to determine the ocurrence and distribution of longidorids infesting vineyards from Portugal. Nematode surveys have been conducted since 2015 on 30 commercial vineyards of the main Controlled Denomination of Origin (DOC) zones of Portugal. Results: The use of an integrative strategy, based on the combination of morphometric and morphological characterizations with molecular analysis using barcode regions such as the ribosomal DNA segments (rDNA) (D2–D3 regions of the 28S gene, ITS1 region, and 18S gene), has allowed the identification of collected longidorid species, associated with severe infestations found in grapevine soils in the studied DOC areas. We emphasize the successful identification and detection of Xiphinema index due to its phytopathological importance. The most important longidorid nematodes detected, in order of decreasing frequency of total soil infestation, were Xiphinema pachtaicum, X. index, X. santos, Xiphinema sp., and X. italiae. Significance: Our study highlights the validity of using an integrative approach based on the combination of morphological data and molecular barcodes for the correct and timely identification of this group of nematode species characterized by high morphological similarity and phenotypic plasticity. The high prevalence of X. index makes this species a severe threat to grapevine production in Portugal.