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Among the main challenges in current viticulture, there is the increasing demand for sustainability in the protection from fungal diseases, such as downy mildew (DM) and powdery mildew (PM). Breeding disease-resistant grapevine varieties is a key strategy for better managing fungicide inputs. This study explores the diversity of grapevine germplasm (cultivated and wild) from Caucasus and neighboring areas to identify genotypes resistant to DM and PM, based on 13 Simple Sequence Repeat (SSR) loci and phenotypical (artificial pathogen inoculation) analysis, and to identify loci associated with DM and PM resistance, via Genome-Wide Association Analysis (GWAS) on Single Nucleotide Polymorphism (SNP) profiles. SSR analysis revealed resistant alleles for 16 out of 88 genotypes. Phenotypic data identified seven DM and 31 PM resistant genotypes. GWAS identified two new loci associated with DM resistance, located on chromosome 15 and 16 (designated as Rpv36 and Rpv37), and two with PM resistance, located on chromosome 6 and 17 (designated as Ren14 and Ren15). The four novel loci identified genomic regions rich in genes related to biotic stress response, such as genes involved in pathogen recognition, signal transduction and resistance response. This study highlights potential candidate genes associated with resistance to DM and PM, providing valuable insights for breeding programs for resistant varieties. To optimize their utilization, further functional characterization studies are recommended. [ABSTRACT FROM AUTHOR]

The Eurasian grapevine (Vitis vinifera), a species cultivated worldwide for high-quality wine production, is extremely susceptible to the agent of downy mildew, Plasmopara viticola. Nevertheless, germplasm from Georgia (Southern Caucasus, the first grapevine domestication centre), characterized by a high genetic variability, showed resistance traits to P. viticola. The cultivar Mgaloblishvili exhibited the most promising phenotype in terms of resistance against P. viticola. Its defence response results in: i) low disease intensity; ii) low sporulation; iii) damaged mycelium; iv) production of antimicrobial compounds such as volatile organic compounds (VOCs), whose effectiveness on the pathogen was evaluated by leafdisc assays. At the transcriptomic level, its resistance mechanism is determined by the differential expression of both resistance and susceptible genes. The resistance genes are related to: i) pathogen recognition through PAMP, DAMP and effector receptors; ii) ethylene signalling pathway; iii) synthesis of antimicrobial compounds (VOCs) and fungal wall degrading enzymes; iv) development of structural barriers (cell wall reinforcement). The first putative susceptible gene was the transcription factor VviLBDIf7 gene, whose validation was carried out by dsRNA (double-stranded RNA) assay. In this work, these unique results on plant-pathogen interaction are reviewed with the aim of developing new strategies to control the disease.

Downy mildew (caused by Plasmopara viticola) is a disease that strongly affect grapevine. To date, the use of fungicide is still the most effective way to prevent the spreading of the pathogen. However, concerns about the safety and the environmental impact of the fungicides make the search of new solutions an urgent problem. Nitrogen nutrition can be one of this. Indeed, P. viticola, that lack of some nitrogen related pathways, can take advantage of plant nitrogen. In this work, we hypothesized that P. viticola could suffer the absence of nitrogen, making the susceptible Pinot Noir cultivar less susceptible to the pathogen. Pinot noir plants were grown in hydroponic solutions with five different nitrogen concentrations (0, 0.05, 1, 2 and 5 mM) and leaf nitrogen content, photosynthetic performance, P. viticola sporulation and gene expression of four nitrogen-related genes (VvLBDIc3, VvLBDIf5, VvLBDIIa3 and VvLBDIIb2) were estimated at three different time points. Leaf nitrogen content, photosynthetic performance and disease severity were reduced at the 0 mM treatment. Nitrogen treatments modulated the expression of genes analysed. VvLBDIc3, VvLBDIf5 and VvLBDIIa3 were overexpressed at low nitrogen concentrations, suggesting a role during nitrogen starvation. While, VvLBDIIb2 was underexpressed at low nitrogen concentrations. A correlation between disease severity and gene espression has been highlighted. These data demonstrated that decrease in nitrogen content can have a positive impact on the incidence of downy mildew, stressing the importance to manage the vineyard nitrogen nutritional status and suggesting an appropriate use of fertilizers, with a beneficial impact for environment and human health. [ABSTRACT FROM AUTHOR]