Contrasting Susceptibilities to Flavescence Dorée in Vitis vinifera, Rootstocks and Wild Vitis Species

Abstract

Flavescence dorée (FD) is a quarantine disease of grapevine, involving interactions between the plants, leafhopper vectors, and FD phytoplasma. Characterizing the susceptibility of vine varieties could limit disease propagation. After extensive surveys in vineyards, we showed that Cabernet Sauvignon (CS) is highly susceptible, with a high proportion of symptomatic branches and phytoplasma titers, in contrast to Merlot (M). Localized insect transmissions and grafting showed that phytoplasma circulate in the whole plant in the CS cultivar, but in M they are restricted to the transmission point. Insect-mediated transmission under high confinement mimicking natural conditions confirmed these phenotypes and allowed the classification of 28 Vitis accessions into three distinct categories, according to the percentage of infected plants and their phytoplasma titers. Reduced symptoms, low phytoplasma titers, and low percentages of infected plants were found to be associated in the Vitis vinifera cultivars tested. Interestingly, the low susceptibility of M was observed for one of its parents, i.e., Magdeleine Noire des Charentes. Rootstocks and their Vitis parents, although having high percentages of infected plants and intermediate to high phytoplasma titers, shared a symptomless response. This is troubling, because rootstocks can constitute a silent reservoir of contamination in mother plants or when they grow wild nearby vineyards. Altogether, data suggest distribution of genetic traits within the Vitis genus involved in insect-mediated phytoplasma transmission, multiplication, circulation, and symptom development.

Flavescence Dorée Phytoplasma Has Multiple ftsH Genes that Are Differentially Expressed in Plants and Insects

“…Indeed, comparing the two pathosystems allowed us to determine if there were any differences in the expression of ftsH genes in the natural hosts as compared to the experimental ones. The presence of FDP in the different samples was verified by a qPCR test [36], and the determined phytoplasma titers varied between 1.07 × 10 +05 and 2.17 × 10 +05 phytoplasma/mgFW in grapevine (mean 1.30 × 10 +05 ), 2.83x10 +06 and 5.27 × 10 +06 phytoplasma/insect in S. titanus (mean 4.11 × 10 +06 ), 1.13 × 10 +06 and 3.74 × 10 +06 phytoplasma/mgFW in broad bean (mean 2.56 × 10 +06 ), and 2.65 × 10 +04 and 1.4 × 10 +05 phytoplasma/insect in E. variegatus (mean 5.79 × 10 +04 ). Healthy samples, either plant or insect, did not show any amplification.…”

“…E. variegatus were reared on oat and broad bean while S. titanus natural vectors was reared on grapevine (Cabernet Sauvignon and Riparia Gloire de Montpellier). After hatching, S. titanus were infected by feeding on infected broad bean for six days (125 insects per broad bean showing symptoms) followed by a latency period of 4 weeks on grapevine (Cabernet Sauvignon) under confined greenhouse conditions [36]. After this latency period, seven S. titanus insects were encaged on each two months old healthy grapevine for one week to obtain inoculated grapevines.…”

Conventional and novel approaches for managing “flavescence dorée” in grapevine: knowledge gaps and future prospects

“…The use of tolerant plant material is often referred to as a promising approach for phytoplasma‐associated field disease control (Seemüller & Harries, ; Jarausch et al ., ). However, care must be taken, because symptomless infected grapevines and rootstocks may contribute to disease dispersion (Eveillard et al ., ). Therefore, although tolerant plants might be an appealing complement to other FD management methodologies, it is important to guarantee that these plants would not represent phytoplasma reservoirs constituting a masked hotspot.…”

“…Susceptibility may be linked to morphological and physiological differences in the plant, which are ultimately determined by the genetic background of each cultivar, and also on how they respond to the environment in which they are grown. It Plant Pathology (2019) 68, 3-17 may also be linked to their response to specific phytoplasma effectors and how these interact with the host plant (Eveillard et al, 2016). Thus, in order to understand the differences in susceptibility to FD, it is important to look at the molecular aspects of the host as well as of the pathogen at a genomic, transcriptomic, proteomic and metabolomic level, as described below.…”

“…This source of resistance would have the great advantage that the commercial traits of the cultivar (scion) remain unchanged. However, a recent study has shown that rootstocks may carry high phytoplasma titres, potentially constituting a silent reservoir of infection (Eveillard et al, 2016).…”