Integrative taxonomic approach and molecular phylogeny for identification of dagger and needle nematode species infesting grapevine soils in Portugal.

Abstract

“Dagger” (Xiphinema spp.) and “needle” (Longidorus spp., Paralongidorus spp.) nematodes are one of the most economically important parasitic nematode groups in grapevine worldwide. They are polyphagous root ectoparasites causing severe damage to plants by their direct feeding, and in addition some species can transmit plant viruses. Grapevine fanleaf virus (GFLV) is transmitted by Xiphinema index, and it is one of the most economically important viral diseases affecting grapevine in many Mediterranean grapevine growing regions. Nematode surveys have been conducted from 2015 to 2017 during the spring and autumn seasons in the main Portuguese grapevine-growing areas. An integrative taxonomic approach based on the combination of morphometric and morphological characterizations with molecular analysis using ribosomal DNA (rDNA) sequences from ITS regions and D2–D3 expansion segments of the 28S gene were used for species delimitation and identification. A high biodiversity of longidorid nematode species was found, higher in dagger than needle nematodes. Xiphinema pachtaicum, X. santos and X. index are the most frequent dagger nematodes found in Portuguese vineyards, while relatively to needle nematodes L. vineacola is the most common species found. Severe nematode infestations were found in grapevine soils in the oldest vineyard regions, highlighting X. index by its phytopathological importance. Disease symptoms were observed on aboveground plant parts of the infected grapevines with X. index, displaying a yellow mosaic pattern in leaves, characteristic of infections by GFLV.