Topic: Towards an understanding of the Grapevine Pinot gris virus pathosystem: a study of transmission by the vector mite Colomerus vitis
Dates: 1 November 2024 – 31 October 2027
CBGP supervisors: D. Navia & P. Augé
University : Institut Agro, Montpellier

The identification of strategies for managing phytoviruses depends on an understanding of epidemiological aspects, and in particular on a thorough knowledge of vectors and their interactions within the pathosystem. This PhD project focuses on the Grapevine Pinot Gris virus (GPGV) – Colomerus vitis mite – and grapevine pathosystem. GPGV is an emerging phytovirus in grapevines, associated with Pinot Gris disease (PGD), the vector-related aspects of which are still poorly understood. To date, the only identified vector of GPGV is the Colomerus vitis mite, a pest belonging to the family Eriophyidae. The overall aim of the project is to fill a number of gaps in our understanding of GPGV transmission by the C. vitis mite.

Three objectives are proposed, which will serve to improve both fundamental and practical knowledge, thereby enabling stakeholders in the wine industry to better manage this vector. The trials will comprise both controlled laboratory studies and field trials. We therefore propose:

1. to investigate the vector competence of the two C. vitis genetic lineages (G1 and G5) most prevalent in France for the transmission of GPGV. The hypothesis is that the two lineages exhibit different transmission efficiencies.
2. to study virus-vector interactions within the GPGV pathosystem under controlled conditions, to assess the mode of GPGV transmission by C. vitis and to determine the main transmission parameters (e.g. acquisition time).
3. to assess the spread of GPGV via the C. vitis vector within and between plots.

The hypothesis is that the diversity of the flora in and around vineyards could influence the spatial distribution of the vector and, consequently, of the virus. The strategies for achieving the three proposed objectives are as follows: transmission trials and laboratory analyses will be conducted at the UMR CBGP; the transmission efficiency of GPGV will be assessed for the two dominant C. vitis genetic lineages in France (G1 and G5) on Pinot Noir or Vermentino grape varieties, chosen to express different symptom patterns and to be susceptible to erinosis.

To study the potential of C. vitis to transmit GPGV, three parameters will be determined:

1. the acquisition window (PAA);
2. the inoculation window (PAI);
3. transmission efficiency.

The mode of transmission will be investigated using transmission electron microscopy. Sentinel plants will be used to study the intra- and inter-plot spread of GPGV. The study will be conducted on two groups of plots, located in two wine-growing regions with different climatic conditions: Languedoc/Provence and Champagne. Vector dispersal will also be studied using water traps for airborne eriophyids, as well as a method for tracking C. vitis mites labelled with albumin.

This is a multidisciplinary project and will be co-led by Marie-Stéphane Tixier (acarology, ecology) at Institut Agro Montpellier; co-supervised by Olivier Lemaire (plant pathology, virology) at INRAE Grand-Est Colmar and Anne-Sophie Spilmont (virology, biotic and abiotic decline, imaging) at IFV.