Alain Bouquet

Genetic dissection of a TIR-NB-LRR locus from the wild North American grapevine species Muscadinia rotundifolia identifies paralogous genes conferring resistance to major fungal and oomycete pathogens in cultivated grapevine.

The most economically important diseases of grapevine cultivation worldwide are caused by the fungal pathogen powdery mildew (Erysiphe necator syn. Uncinula necator) and the oomycete pathogen downy mildew (Plasmopara viticola). Currently, grapegrowers rely heavily on the use of agrochemicals to minimize the potentially devastating impact of these pathogens on grape yield and quality. The wild North American grapevine species Muscadinia rotundifolia was recognized as early as 1889 to be resistant to both powdery and downy mildew. We have now mapped resistance to these two mildew pathogens in M. rotundifolia to a single locus on chromosome 12 that contains a family of seven TIR-NB-LRR genes. We further demonstrate that two highly homologous (86% amino acid identity) members of this gene family confer strong resistance to these unrelated pathogens following genetic transformation into susceptible Vitis vinifera winegrape cultivars. These two genes, designated resistance to Uncinula necator (MrRUN1) and resistance to Plasmopara viticola (MrRPV1) are the first resistance genes to be cloned from a grapevine species. Both MrRUN1 and MrRPV1 were found to confer resistance to multiple powdery and downy mildew isolates from France, North America and Australia; however, a single powdery mildew isolate collected from the south-eastern region of North America, to which M. rotundifolia is native, was capable of breaking MrRUN1-mediated resistance. Comparisons of gene organization and coding sequences between M. rotundifolia and the cultivated grapevine V. vinifera at the MrRUN1/MrRPV1 locus revealed a high level of synteny, suggesting that the TIR-NB-LRR genes at this locus share a common ancestor.

QTLs for fertility in table grape (Vitis vinifera L.)

Fertility (number of inflorescences per shoot) is a trait of major importance for grapevine breeding. We present and compare the results of quantitative trait locus (QTL) detection for fertility in two table grape progenies, MTP3140 and MTP3234. Novel parental and consensus maps were built for MTP3140. We found a main QTL on linkage group (LG) 5 in both progenies, which was also the most stable one across years. It explained up to 18.5% of the total intra-cross phenotypic variance. Three other QTLs, one on LG 5 and two on LG 14, were repeated over years but were found in a single progeny. Our results suggest that QTLs effect was mainly additive. The prospects for testing candidate genes are discussed as well as the potential interest of these results for marker-assisted selection.

Selection and Application of Resistant Germplasm for Grapevine Nematodes Management

The status of selection studies on resistant grapevine rootstocks for management of root-knot nematodes Meloidogyne spp. and of Xiphinema index, vector of Grapevine fanleaf virus, is reviewed. The biology, ecology, symptomatology and control of root-knot nematodes are revised, for application in the selection and breeding of resistant rootstocks. Data on resistant Vitis and Muscadinia material, as well as on the genetics, mechanisms and durability of resistance are also provided. The pathogenicity of X. index and of other grapevine nematode vectors is then summarized, as concerns the biology, transmission and classical nematode control. Breeding efforts for selection of grape resistant rootstocks are then reported, focusing on resistance features of M. rotundifolia and V. vinifera × M. rotundifolia F1 hybrids, obtained in California and France, and new prospects are foreseen. Resistance to other nematodes and rootstock applications for control of multiple nematode pests are also discussed.

MICROPROPAGATION OF THE GRAPEVINE (Vitis spp.)

During the past decades, rapid progress has been made in the application of plant biotechnology to agriculture and horticulture, mainly with the assistance from botanists, plant physiologists and molecular geneticists who lack expertise in crop plants, crop husbandry or crop breeding. The literature is pervaded by a feeling that only a few trivial technical problems remain and we are at the threshold of a latter-day agrarian revolution. This is wishful thinking Temperate perennial fruit crops, and grapevines in particular, are subject to special circumstances that can affect or limit the use of tissue culture methods for both plant propagation and plant improvement. Substantial benefits will accrue the grapegrowing industry from further development of tissue culture but advocacy forin vitrotechniques must be tempered by an appreciation of the historical, biological, technical and economic realities of viticultural production.

Antibiotic Sensitivity of Grapevine: A Comparison Between the Effect of Hygromycin and Kanamycin on Shoot Development of Transgenic 110 Richter Rootstock (Vi tis B erlandieri x Vi tis rupestris)

The effects of kanamycin and hygromycin on the in vitro development of 110 Richter rootstock (Vitis Berlandieri x V. rupestris) and derived transgenic clones were studied in order to evaluate their suitability as selectable markers for grapevine transformation. Transgenic clones carried both the neomycin phosphotransferase gene (nptll) under the nopaline synthase promoter (pNOS) and the hygromycin phosphotransferase (hpt) gene under the cauliflower mosaic virus 35S promoter (p35S), which confer the ability to grow in the presence of kanamycin and hygromycin, respectively. Even incorporated at low concentrations, both antibiotics strongly inhibited explant development for the control clone, but hygromycin appeared much more toxic. Whereas growth was stopped with 1 μg/mL hygromycin, 16 μg/mL kanamycin was required to block shoot development. Contrary to the control plants, transgenic clones exhibited a greater tolerance to hygromycin than kanamycin. In some transgenic clones the level of resistance conferred by the nptll was not significantly advantageous in terms of their ability to grow in the presence of kanamycin. Conversely, the hpt gene provided a strong level of tolerance to hygromycin in all transgenic clones, some clones developing up to 64 μg/mL hygromycin. Strategies for selection of grapevine putative transformants with these two antibiotics are discussed.