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Spatial Distribution of the Dagger Nematode Xiphinema index and Its Associated Grapevine fanleaf virus in French Vineyard

First, second, and fifth authors: INRA, Agrocampus Rennes, UMR1099 BiO3P (Biology of Organisms and Populations applied to Plant Protection), F-35653 Le Rheu, France; fourth and seventh authors: ENITA de Bordeaux, UMR SV (Santé Végétale), F-33170 Gradignan, France; third author: Laboratory of Nematology, Wageningen University, 6709 PD Wageningen, The Netherlands; and sixth author: INRA, UMR IBSV (Biotic Interactions and Plant Health), Equipe “Interactions Plantes-Nématodes,” F-06903 Sophia-Antipolis, France.

The nematode Xiphinema index is, economically, the major virus vector in viticulture, transmitting specifically the Grapevine fanleaf virus (GFLV), the most severe grapevine virus disease worldwide. Increased knowledge of the spatial distribution of this nematode, both horizontally and vertically, and of correlative GFLV plant infections, is essential to efficiently control the disease. In two infested blocks of the Bordeaux vineyard, vertical distribution data showed that the highest numbers of individuals occurred at 40 to 110 cm depth, corresponding to the two layers where the highest densities of fine roots were observed. Horizontal distribution based on a 10 × 15 m grid sampling procedure revealed a significant aggregative pattern but no significant neighborhood structure of nematode densities. At a finer scale (≈2 × 2 m), nematode sampling performed in a third block confirmed a significant aggregative pattern, with patches of 6 to 8 m diameter, together with a significant neighborhood structure of nematode densities, thus identifying the relevant sampling scale to describe the nematode distribution. Nematode patches correlate significantly with those of GFLV-infected grapevine plants. Finally, nematode and virus spread were shown to extend preferentially parallel to vine rows, probably due to tillage during mechanical weeding.