Identification of two novel powdery mildew resistance loci, Ren6 and Ren7, from the wild Chinese grape species Vitis piasezkii

Novel loci associated with resistance to downy and powdery mildew in grapevine

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.

Phenolic profile changes of grapevine leaves infected with Erysiphe necator

BACKGROUND

Powdery mildew in grapevine is caused by Erysiphe necator and its control requires many chemical treatments. Numerous efforts are being made to improve disease management to achieve crop sustainability goals. The exogenous induction of plant immune responses is one of the most encouraging strategies currently being developed. The objective of this research was to analyse differences in phenolic compound concentrations in E. necator-infected leaves of two varieties of Vitis vinifera, Tempranillo and Tempranillo Blanco, using ultra performance liquid chromatography coupled with mass spectrometry. To understand the susceptibility of the varieties, in vitro assays using whole leaves were done.

RESULTS

Differences in susceptibility between varieties were found in the early stage of the disease. In both varieties, total phenolic compounds were higher in infected leaves; however, hydroxycinnamic acid, anthocyanins and stilbenes were higher only in Tempranillo. Twenty-six compounds showed differential responses to the fungal disease in Tempranillo, but only two in Tempranillo Blanco: syringa resinol, which was not detected in diseased leaves; and gallocatechin, which increased at 5 days post inoculation. In Tempranillo, four anthocyanidins, six hydroxycinnamic acids, mainly feruloyl derivates, and epigallocatechin gallate were higher in infected leaves at the beginning of the infection, whereas (-)-epicatechin and protocatechuic hexoside contents were lower.

CONCLUSION

Disease-induced changes in phenolic compound biosynthesis were found. The increase in anthocyanidin content and flavan-3-ol galloylation could have a role in delaying E. necator growth in Tempranillo. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

QTL detection and candidate gene analysis of grape white rot resistance by interspecific grape (Vitis vinifera L. × Vitis davidii Foex.) crossing

Grape white rot, a devastating disease of grapevines caused by Coniella diplodiella (Speg.) Sacc., leads to significant yield losses in grape. Breeding grape cultivars resistant to white rot is essential to reduce the regular use of chemical treatments. In recent years, Chinese grape species have gained more attention for grape breeding due to their high tolerance to various biotic and abiotic factors along with changing climatic conditions. In this study, we employed whole-genome resequencing (WGR) to genotype the parents of 'Manicure Finger' (Vitis vinifera, female) and '0940' (Vitis davidii, male), along with 101 F₁ mapping population individuals, thereby constructing a linkage genetic map. The linkage map contained 9337 single-nucleotide polymorphism (SNP) markers with an average marker distance of 0.3 cM. After 3 years of phenotypic evaluation of the progeny for white rot resistance, we confirmed one stable quantitative trait locus (QTL) for white rot resistance on chromosome 3, explaining up to 17.9% of the phenotypic variation. For this locus, we used RNA-seq to detect candidate gene expression and identified PR1 as a candidate gene involved in white rot resistance. Finally, we demonstrated that recombinant PR1 protein could inhibit the growth of C. diplodiella and that overexpression of PR1 in susceptible V. vinifera increased grape resistance to the pathogen.

Discovery and genome-guided mapping of REN12 from Vitis amurensis, conferring strong, rapid resistance to grapevine powdery mildew

Powdery mildew resistance genes restrict infection attempts at different stages of pathogenesis. Here, a strong and rapid powdery mildew resistance phenotype was discovered from Vitis amurensis 'PI 588631' that rapidly stopped over 97% of Erysiphe necator conidia, before or immediately after emergence of a secondary hypha from appressoria. This resistance was effective across multiple years of vineyard evaluation on leaves, stems, rachises, and fruit and against a diverse array of E. necator laboratory isolates. Using core genome rhAmpSeq markers, resistance mapped to a single dominant locus (here named REN12) on chromosome 13 near 22.8-27.0 Mb, irrespective of tissue type, explaining up to 86.9% of the phenotypic variation observed on leaves. Shotgun sequencing of recombinant vines using skim-seq technology enabled the locus to be further resolved to a 780 kb region, from 25.15 to 25.93 Mb. RNASeq analysis indicated the allele-specific expression of four resistance genes (NLRs) from the resistant parent. REN12 is one of the strongest powdery mildew resistance loci in grapevine yet documented, and the rhAmpSeq sequences presented here can be directly used for marker-assisted selection or converted to other genotyping platforms. While no virulent isolates were identified among the genetically diverse isolates and wild populations of E. necator tested here, NLR loci like REN12 are often race-specific. Thus, stacking of multiple resistance genes and minimal use of fungicides should enhance the durability of resistance and could enable a 90% reduction in fungicides in low-rainfall climates where few other pathogens attack the foliage or fruit.

Genetic changes in the genus Vitis and the domestication of vine

The genus Vitis belongs to the Vitaceae family and is divided into two subgenera: Muscadinia and Vitis, the main difference between these subgenera being the number of chromosomes. There are many hypotheses about the origin of the genus, which have been formed with archaeological studies and lately with molecular analyses. Even though there is no consensus on the place of origin, these studies have shown that grapes have been used by man since ancient times, starting later on its domestication. Most studies point to the Near East and Greece as the beginning of domestication, current research suggests it took place in parallel in different sites, but in all cases Vitis vinifera (L.) subsp. sylvestris [Vitis vinifera (L.) subsp. sylvestris (Gmelin) Hagi] seems to be the species chosen by our ancestors to give rise to the now known Vitis vinifera (L.) subsp. vinifera [=sativa (Hegi)= caucasica (Vavilov)]. Its evolution and expansion into other territories followed the formation of new empires and their expansion, and this is where the historical importance of this crop lies. In this process, plants with hermaphrodite flowers were preferentially selected, with firmer, sweeter, larger fruits of different colors, thus favoring the selection of genes associated with these traits, also resulting in a change in seed morphology. Currently, genetic improvement programs have made use of wild species for the introgression of disease resistance genes and tolerance to diverse soil and climate environments. In addition, the mapping of genes of interest, both linked to agronomic and fruit quality traits, has allowed the use of molecular markers for assisted selection. Information on the domestication process and genetic resources help to understand the gene pool available for the development of cultivars that respond to producer and consumer requirements.

Semi-Targeted Profiling of the Lipidome Changes Induced by Erysiphe Necator in Disease-Resistant and Vitis vinifera L. Varieties

The ascomycete Erysiphe necator is a serious pathogen in viticulture. Despite the fact that some grapevine genotypes exhibit mono-locus or pyramided resistance to this fungus, the lipidomics basis of these genotypes' defense mechanisms remains unknown. Lipid molecules have critical functions in plant defenses, acting as structural barriers in the cell wall that limit pathogen access or as signaling molecules after stress responses that may regulate innate plant immunity. To unravel and better understand their involvement in plant defense, we used a novel approach of ultra-high performance liquid chromatography (UHPLC)-MS/MS to study how E. necator infection changes the lipid profile of genotypes with different sources of resistance, including BC4 (Run1), "Kishmish vatkhana" (Ren1), F26P92 (Ren3; Ren9), and "Teroldego" (a susceptible genotype), at 0, 24, and 48 hpi. The lipidome alterations were most visible at 24 hpi for BC4 and F26P92, and at 48 hpi for "Kishmish vatkhana". Among the most abundant lipids in grapevine leaves were the extra-plastidial lipids: glycerophosphocholine (PCs), glycerophosphoethanolamine (PEs) and the signaling lipids: glycerophosphates (Pas) and glycerophosphoinositols (PIs), followed by the plastid lipids: glycerophosphoglycerols (PGs), monogalactosyldiacylglycerols (MGDGs), and digalactosyldiacylglycerols (DGDGs) and, in lower amounts lyso-glycerophosphocholines (LPCs), lyso-glycerophosphoglycerols (LPGs), lyso-glycerophosphoinositols (LPIs), and lyso-glycerophosphoethanolamine (LPEs). Furthermore, the three resistant genotypes had the most prevalent down-accumulated lipid classes, while the susceptible genotype had the most prevalent up-accumulated lipid classes.

Secondary and primary metabolites reveal putative resistance-associated biomarkers against Erysiphe necator in resistant grapevine genotypes

Numerous fungicide applications are required to control Erysiphe necator, the causative agent of powdery mildew. This increased demand for cultivars with strong and long-lasting field resistance to diseases and pests. In comparison to the susceptible cultivar 'Teroldego', the current study provides information on some promising disease-resistant varieties (mono-locus) carrying one E. necator-resistant locus: BC4 and 'Kishmish vatkana', as well as resistant genotypes carrying several E. necator resistant loci (pyramided): 'Bianca', F26P92, F13P71, and NY42. A clear picture of the metabolites' alterations in response to the pathogen is shown by profiling the main and secondary metabolism: primary compounds and lipids; volatile organic compounds and phenolic compounds at 0, 12, and 48 hours after pathogen inoculation. We identified several compounds whose metabolic modulation indicated that resistant plants initiate defense upon pathogen inoculation, which, while similar to the susceptible genotype in some cases, did not imply that the plants were not resistant, but rather that their resistance was modulated at different percentages of metabolite accumulation and with different effect sizes. As a result, we discovered ten up-accumulated metabolites that distinguished resistant from susceptible varieties in response to powdery mildew inoculation, three of which have already been proposed as resistance biomarkers due to their role in activating the plant defense response.

The grape powdery mildew resistance loci Ren2, Ren3, Ren4D, Ren4U, Run1, Run1.2b, Run2.1, and Run2.2 activate different transcriptional responses to Erysiphe necator

Multiple grape powdery mildew (PM) genetic resistance (R) loci have been found in wild grape species. Little is known about the defense responses associated with each R locus. In this study, we compare the defense mechanisms associated with PM resistance in interspecific crosses segregating for a single R locus from Muscadinia rotundifolia (Run1, Run1.2b, Run2.1, Run2.2), Vitis cinerea (Ren2), V. romanetii (Ren4D and Ren4U), and the interspecific hybrid Villard blanc (Ren3). By combining optical microscopy, visual scoring, and biomass estimation, we show that the eight R loci confer resistance by limiting infection at different stages. We assessed the defense mechanisms triggered in response to PM at 1 and 5 days post-inoculation (dpi) via RNA sequencing. To account for the genetic differences between species, we developed for each accession a diploid synthetic reference transcriptome by incorporating into the PN40024 reference homozygous and heterozygous sequence variants and de novo assembled transcripts. Most of the R loci exhibited a higher number of differentially expressed genes (DEGs) associated with PM resistance at 1 dpi compared to 5 dpi, suggesting that PM resistance is mostly associated with an early transcriptional reprogramming. Comparison of the PM resistance-associated DEGs showed a limited overlap between pairs of R loci, and nearly half of the DEGs were specific to a single R locus. The largest overlap of PM resistance-associated DEGs was found between Ren3 ⁺, Ren4D ⁺, and Ren4U ⁺ genotypes at 1 dpi, and between Ren4U ⁺ and Run1 ⁺ accessions at 5 dpi. The Ren3 ⁺, Ren4D ⁺, and Ren4U ⁺ were also found to have the highest number of R locus-specific DEGs in response to PM. Both shared and R locus-specific DEGs included genes from different defense-related categories, indicating that the presence of E. necator triggered distinct transcriptional responses in the eight R loci.

Transcriptome analysis reveals pathogenesis-related gene 1 pathway against salicylic acid treatment in grapevine (Vitis vinifera L)

Salicylic acid (SA) is a well-studied phenolic plant hormone that plays an important role in plant defense against the hemi-biothrophic and biothrophic pathogens and depends on the living cells of host for the successful infection. In this study, a pathogenesis test was performed between Vitis davidii and V. vinifera cultivars against grape white rot disease (Coniella diplodiella). V. davidii was found to be resistant against this disease. SA contents were found to be higher in the resistant grape cultivar after different time points. RNA-seq analysis was conducted on susceptible grapevine cultivars after 12, 24, and 48 h of SA application with the hypothesis that SA may induce defense genes in susceptible cultivars. A total of 511 differentially expressed genes (DEGs) were identified from the RNA-seq data, including some important genes, VvWRKY1/2, VvNPR1, VvTGA2, and VvPR1, for the SA defense pathway. DEGs related to phytohormone signal transduction and flavonoid biosynthetic pathways were also upregulated. The quantitative real-time PCR (qRT-PCR) results of the significantly expressed transcripts were found to be consistent with the transcriptome data, with a high correlation between the two analyses. The pathogenesis-related gene 1 (VvPR1), which is an important marker gene for plant defense, was selected for further promoter analysis. The promoter sequence showed that it contains some important cis-elements (W-box, LS7, as-1, and TCA-element) to recruit the transcription factors VvWRKY, VvNPR1, and VvTGA2 to express the VvPR1 gene in response to SA treatment. Furthermore, the VvPR1 promoter was serially deleted into different fragments (-1,837, -1,443, -1,119, -864, -558, -436, and -192 ) bp and constructed vectors with the GUS reporter gene. Deletion analysis revealed that the VvPR1 promoter between -1837 bp to -558 bp induced significant GUS expression with respect to the control. On the basis of these results, the -558 bp region was assumed to be an important part of the VvPR1 promoter, and this region contained the important cis-elements related to SA, such as TCA-element (-1,472 bp), LS7 (-1,428 bp), and as-1 (-520 bp), that recruit the TFs and induce the expression of the VvPR1 gene. This study expanded the available information regarding SA-induced defense in susceptible grapes and recognized the molecular mechanisms through which this defense might be mediated.

Phenotyping for QTL identification: A case study of resistance to Plasmopara viticola and Erysiphe necator in grapevine

Vitis vinifera is the most widely cultivated grapevine species. It is highly susceptible to Plasmopara viticola and Erysiphe necator, the causal agents of downy mildew (DM) and powdery mildew (PM), respectively. Current strategies to control DM and PM mainly rely on agrochemical applications that are potentially harmful to humans and the environment. Breeding for resistance to DM and PM in wine grape cultivars by introgressing resistance loci from wild Vitis spp. is a complementary and more sustainable solution to manage these two diseases. During the last two decades, 33 loci of resistance to P. viticola (Rpv) and 15 loci of resistance to E. necator (Ren and Run) have been identified. Phenotyping is salient for QTL characterization and understanding the genetic basis of resistant traits. However, phenotyping remains a major bottleneck for research on Rpv and Ren/Run loci and disease resistance evaluation. A thorough analysis of the literature on phenotyping methods used for DM and PM resistance evaluation highlighted phenotyping performed in the vineyard, greenhouse or laboratory with major sources of variation, such as environmental conditions, plant material (organ physiology and age), pathogen inoculum (genetic and origin), pathogen inoculation (natural or controlled), and disease assessment method (date, frequency, and method of scoring). All these factors affect resistance assessment and the quality of phenotyping data. We argue that the use of new technologies for disease symptom assessment, and the production and adoption of standardized experimental guidelines should enhance the accuracy and reliability of phenotyping data. This should contribute to a better replicability of resistance evaluation outputs, facilitate QTL identification, and contribute to streamline disease resistance breeding programs.

Haplotype-resolved powdery mildew resistance loci reveal the impact of heterozygous structural variation on NLR genes in Muscadinia rotundifolia

Muscadinia rotundifolia cv. Trayshed is a valuable source of resistance to grape powdery mildew. It carries 2 powdery mildew resistance-associated genetic loci, Run1.2 on chromosome 12 and Run2.2 on chromosome 18. The purpose of this study was to identify candidate resistance genes associated with each haplotype of the 2 loci. Both haplotypes of each resistance-associated locus were identified, phased, and reconstructed. Haplotype phasing allowed the identification of several structural variation events between haplotypes of both loci. Combined with a manual refinement of the gene models, we found that the heterozygous structural variants affected the gene content, with some resulting in duplicated or hemizygous nucleotide-binding leucine-rich repeat genes. Heterozygous structural variations were also found to impact the domain composition of some nucleotide-binding leucine-rich repeat proteins. By comparing the nucleotide-binding leucine-rich repeat proteins at Run1.2 and Run2.2 loci, we discovered that the 2 loci include different numbers and classes of nucleotide-binding leucine-rich repeat genes. To identify powdery mildew resistance-associated genes, we performed a gene expression profiling of the nucleotide-binding leucine-rich repeat genes at Run1.2b and Run2.2 loci with or without powdery mildew present. Several nucleotide-binding leucine-rich repeat genes were constitutively expressed, suggesting a role in powdery mildew resistance. These first complete, haplotype-resolved resistance-associated loci and the candidate nucleotide-binding leucine-rich repeat genes identified by this study are new resources that can aid the development of powdery mildew-resistant grape cultivars.

Powdery Mildew Resistance Genes in Vines: An Opportunity to Achieve a More Sustainable Viticulture

Grapevine (Vitis vinifera) is one of the main fruit crops worldwide. In 2020, the total surface area planted with vines was estimated at 7.3 million hectares. Diverse pathogens affect grapevine yield, fruit, and wine quality of which powdery mildew is the most important disease prior to harvest. Its causal agent is the biotrophic fungus Erysiphe necator, which generates a decrease in cluster weight, delays fruit ripening, and reduces photosynthetic and transpiration rates. In addition, powdery mildew induces metabolic reprogramming in its host, affecting primary metabolism. Most commercial grapevine cultivars are highly susceptible to powdery mildew; consequently, large quantities of fungicide are applied during the productive season. However, pesticides are associated with health problems, negative environmental impacts, and high costs for farmers. In paralleled, consumers are demanding more sustainable practices during food production. Therefore, new grapevine cultivars with genetic resistance to powdery mildew are needed for sustainable viticulture, while maintaining yield, fruit, and wine quality. Two main gene families confer resistance to powdery mildew in the Vitaceae, Run (Resistance to Uncinula necator) and Ren (Resistance to Erysiphe necator). This article reviews the powdery mildew resistance genes and loci and their use in grapevine breeding programs.

GWAS Reveals a Novel Candidate Gene CmoAP2/ERF in Pumpkin (Cucurbita moschata) Involved in Resistance to Powdery Mildew

Pumpkin (Cucurbita moschata Duchesne ex Poir.) is a multipurpose cash crop rich in antioxidants, minerals, and vitamins; the seeds are also a good source of quality oils. However, pumpkin is susceptible to the fungus Podosphaera xanthii, an obligate biotrophic pathogen, which usually causes powdery mildew (PM) on both sides of the leaves and reduces photosynthesis. The fruits of infected plants are often smaller than usual and unpalatable. This study identified a novel gene that involves PM resistance in pumpkins through a genome-wide association study (GWAS). The allelic variation identified in the CmoCh3G009850 gene encoding for AP2-like ethylene-responsive transcription factor (CmoAP2/ERF) was proven to be involved in PM resistance. Validation of the GWAS data revealed six single nucleotide polymorphism (SNP) variations in the CmoAP2/ERF coding sequence between the resistant (IT 274039 [PMR]) and the susceptible (IT 278592 [PMS]). A polymorphic marker (dCAPS) was developed based on the allelic diversity to differentiate these two haplotypes. Genetic analysis in the segregating population derived from PMS and PMR parents provided evidence for an incomplete dominant gene-mediated PM resistance. Further, the qRT-PCR assay validated the elevated expression of CmoAP2/ERF during PM infection in the PMR compared with PMS. These results highlighted the pivotal role of CmoAP2/ERF in conferring resistance to PM and identifies it as a valuable molecular entity for breeding resistant pumpkin cultivars.

A Comparative Analysis of Microbe-Based Technologies Developed at ICAR-NBAIM Against Erysiphe necator Causing Powdery Mildew Disease in Grapes (Vitis vinifera L.)

Globally, Erysiphe necator causing powdery mildew disease in grapevines (Vitis vinifera L.) is the second most important endemic disease, causing huge economic losses every year. At present, the management of powdery mildew in grapes is largely dependent upon the use of chemical fungicides. Grapes are being considered as one of the high pesticide-demanding crops. Looking at the residual impact of toxic chemical pesticides on the environment, animal, and human health, microbe-based strategies for control of powdery mildew is an emerging technique. It offers an environment-friendly, residue-free, and effective yet safer approach to control powdery mildew disease in grapes. The mode of action is relatively diverse as well as specific to different pathosystems. Hence, the aim of this study was to evaluate the microbe-based technologies, i.e., Eco-pesticide^®, Bio-Pulse^®, and Bio-Care 24^® developed at the Plant-Microbe Interaction and Rhizosphere Biology Lab, ICAR-NBAIM, Kushmaur, against grape powdery mildew and to integrate these technologies with a safer fungicide (sulfur) to achieve better disease control under organic systems of viticulture. The experiments were conducted at four different locations, namely, the vineyards of ICAR-NRCG, Rajya Draksha Bagayatdar Sangh (MRDBS), and two farmers' fields at Narayangaon and Junnar in the Pune district of Maharashtra. A significantly lower percent disease index (PDI) was recorded on the leaves of grape plants treated with Eco-Pesticide^®/sulfur (22.37) followed by Bio-Pulse^®/sulfur (22.62) and Bio-Care 24^®/sulfur (24.62) at NRCG. A similar trend was observed with the lowest PDI on bunches of Eco-pesticide^® /sulfur-treated plants (24.71) followed by Bio-Pulse^®/sulfur (24.94) and Bio-Care^®/sulfur (26.77). The application of microbial inoculants singly or in combination with sulfur has a significant positive impact on the qualitative parameters such as pH, total soluble solids (TSS), acidity, berry diameter, and berry length of the grapes at different locations. Among all the treatments, the Bio-Pulse^®/sulfur treatment showed the highest yield per vine (15.02 kg), which was on par with the treatment Eco-Pesticide^®/sulfur (14.94). When compared with the yield obtained from the untreated control, 2.5 to 3 times more yield was recorded in the plants treated with either of the biopesticides used in combination with sulfur. Even in the case of individual inoculation, the yield per vine was approximately two times higher than the untreated control and water-treated plants across the test locations. Results suggested that microbial technologies not only protect grapevines from powdery mildew but also enhance the quality parameters with increased yield across the test locations.

Genetic Analysis of the Grapevine GATA Gene Family and Their Expression Profiles in Response to Hormone and Downy Mildew Infection

Grapevine (Vitis. vinifera L.) is one of the most economically important fruit crops throughout the world. However, grape production is increasingly impacted by numerous diseases, including downy mildew, caused by the oomycete Plasmopara viticola. In grapevine and other plants, members of the GATA family of transcription factors play key roles in light and phytohormone signaling. However, little is known about their potential roles in biotic defense responses. As a first step, we identified 27 GATA transcription factors in grapevine and defined their transcriptional responses to three biotic stress-related phytohormones (SA, MeJA, and BR) in callus cells, and challenge with P. viticola in a downy mildew-sensitive cultivar, V. vinifera ‘Pinot noir’, and a resistant cultivar, V. piasezkii ‘Liuba-8′. Many of the VvGATA genes had higher expression at 0.5 h after hormones treatments. Moreover, a group of VvGATAs was dramatically induced in ‘Liuba-8′ at 24 post infection by P. viticola. However, the same genes were significantly repressed and showed low expression levels in ‘Pinot noir’. Additionally, VvGATA27 was located in the nucleus and had transcriptional activity. Taken together, the study identified the GATA full gene families in grapes on phylogenetic analysis and protein structure. Moreover, this study provided a basis for discussing the roles of VvGATAs in response to hormones and P. viticola infection. Our results provided evidence for the selection of candidate genes against downy mildew and lay the foundation for further investigation of VvGATA transcription factors.

Extent of wild-to-crop interspecific introgression in grapevine (Vitis vinifera) as a consequence of resistance breeding and implications for the crop species definition

Over the past two centuries, introgression through repeated backcrossing has introduced disease resistance from wild grape species into the domesticated lineage Vitis vinifera subsp. sativa. Introgression lines are being cultivated over increasing vineyard surface areas, as their wines now rival in quality those obtained from preexisting varieties. There is, however, a lot of debate about whether and how wine laws defining commercial product categories, which are based on the classification of V. vinifera and interspecific hybrid grapes, should be revised to accommodate novel varieties that do not fit either category. Here, we developed a method of multilocus genotype analysis using short-read resequencing to identify haplotypic blocks of wild ancestry in introgression lines and quantify the physical length of chromosome segments free-of-introgression or with monoallelic and biallelic introgression. We used this genomic data to characterize species, hybrids and introgression lines and show that newly released resistant varieties contain 76.5-94.8% of V. vinifera DNA. We found that varietal wine ratings are not always commensurate with the percentage of V. vinifera ancestry and linkage drag of wild alleles around known resistance genes persists over at least 7.1-11.5 Mb, slowing down the recovery of the recurrent parental genome. This method also allowed us to identify the donor species of known resistance haplotypes, define the ancestry of wild genetic background in introgression lines with complex pedigrees, validate the ancestry of the historic varieties Concord and Norton, and unravel sample curation errors in public databases.

Analysis of the SC8-0071-014 and sc47-18 loci co-segregated with Ren1 gene in the genotypes of seedless grape varieties

Powdery mildew (Erysiphe necator) is one of the most common and economically significant diseases of grapes. The main method of controlling the disease is pesticide treatment. To reduce chemical treatments, it is necessary to select and introduce resistant varieties into production. DNA markers are currently actively used in the study of grape genetic resources. Seedless grape varieties are highly demanded by consumers. Ren1 is one of the known and mapped vine resistance genes to powdery mildew, inherited from V. vinifera; linked DNA markers for this resistance locus are known. A study of 34 seedless grape genotypes was carried out using DNA markers SC8-0071-014 and sc47-18 co-segregated with Ren1. In the studied sample of varieties, 12 types of alleles were identified in the sc47-18 locus and 9 types of alleles in the SC8-0071-014 locus. Target fragments, according to linked marker loci, indicating the presence of the Ren1 resistance gene, were identified in grape variety Lotus (Kriulyanskiy x Yangi Er).

Construction of a high-density genetic map and detection of a major QTL of resistance to powdery mildew (Erysiphe necator Sch.) in Caucasian grapes (Vitis vinifera L.)

BACKGROUND

Vitis vinifera L. is the most cultivated grapevine species worldwide. Erysiphe necator Sch., the causal agent of grape powdery mildew, is one of the main pathogens affecting viticulture. V. vinifera has little or no genetic resistances against E. necator and the grape industry is highly dependent on agrochemicals. Some Caucasian V. vinifera accessions have been reported to be resistant to E. necator and to have no genetic relationships to known sources of resistance to powdery mildew. The main purpose of this work was the study and mapping of the resistance to E. necator in the Caucasian grapes 'Shavtsitska' and 'Tskhvedianis tetra'.

RESULTS

The Caucasian varieties 'Shavtsitska' and 'Tskhvedianis tetra' showed a strong partial resistance to E. necator which segregated in two cross populations: the resistant genotypes delayed and limited the pathogen mycelium growth, sporulation intensity and number of conidia generated. A total of 184 seedlings of 'Shavtsitska' x 'Glera' population were genotyped through the Genotyping by Sequencing (GBS) technology and two high-density linkage maps were developed for the cross parents. The QTL analysis revealed a major resistance locus, explaining up to 80.15% of the phenotypic variance, on 'Shavtsitska' linkage group 13, which was associated with a reduced pathogen infection as well as an enhanced plant necrotic response. The genotyping of 105 Caucasian accessions with SSR markers flanking the QTL revealed that the resistant haplotype of 'Shavtsitska' was shared by 'Tskhvedianis tetra' and a total of 25 Caucasian grape varieties, suggesting a widespread presence of this resistance in the surveyed germplasm. The uncovered QTL was mapped in the region where the Ren1 locus of resistance to E. necator, identified in the V. vinifera 'Kishmish vatkana' and related grapes of Central Asia, is located. The genetic analysis conducted revealed that the Caucasian grapes in this study exhibit a resistant haplotype different from that of Central Asian grape accessions.

CONCLUSIONS

The QTL isolated in 'Shavtsitska' and present in the Caucasian V. vinifera varieties could be a new candidate gene of resistance to E. necator to use in breeding programmes. It co-localizes with the Ren1 locus but shows a different haplotype from that of grapevines of Central Asia. We therefore consider that the Caucasian resistance locus, named Ren1.2, contains a member of a cluster of R-genes, of which the region is rich, and to be linked with, or possibly allelic, to Ren1.

Grape Transcriptome Response to Powdery Mildew Infection: Comparative Transcriptome Profiling of Chinese Wild Grapes Provides Insights Into Powdery Mildew Resistance

Erysiphe necator, the fungal pathogen of grape powdery mildew disease, poses a great threat to the grape market and the wine industry. To better understand the molecular basis of grape responses to E. necator, we performed comparative transcriptome profiling on two Chinese wild grape accessions with varying degrees of resistance to E. necator. At 6-, 24-, and 96-h postinoculation of E. necator, 2,856, 2,678, and 1,542 differentially expressed genes (DEGs) were identified in the susceptible accession Vitis pseudoreticulata 'Hunan-1', and at those same time points, 1,921, 2,498, and 3,249 DEGs, respectively, were identified in the resistant accession V. quinquangularis 'Shang-24'. 'Hunan-1' had a substantially larger fraction of down-regulated genes than 'Shang-24' at every infection stage. Analysis of DEGs revealed that up-regulated genes were mostly associated with defense response and disease resistance-related metabolite biosynthesis, and such signaling genes were significantly suppressed in 'Hunan-1'. Interestingly, fatty acid biosynthesis- and elongation-related genes were suppressed by the fungus in the 'Shang-24' accession but somehow induced in the 'Hunan-1' accession, consistent with the concept that E. necator is likely to be a fatty acid auxotroph that requires lipids from the host. Moreover, genes involved in biosynthesis and signaling of phytohormones, such as jasmonic acid and cytokinin, as well as genes encoding protein kinases and nucleotide-binding domain leucine-rich repeat proteins, differentially responded to E. necator in the two wild grapes. The variation of gene regulation associated with nutrient uptake by the fungus and with signaling transduction and pathogen recognition suggests a multilayered regulatory network that works in concert to assist in the establishment of fungal pathogen infections.

Transcriptional, hormonal, and metabolic changes in susceptible grape berries under powdery mildew infection

Grapevine (Vitis vinifera) berries are extremely sensitive to infection by the biotrophic pathogen Erysiphe necator, causing powdery mildew disease with deleterious effects on grape and wine quality. The combined analysis of the transcriptome and metabolome associated with this common fungal infection has not been previously carried out in any fruit. In order to identify the molecular, hormonal, and metabolic mechanisms associated with infection, healthy and naturally infected V. vinifera cv. Carignan berries were collected at two developmental stages: late green (EL33) and early véraison (EL35). RNA sequencing combined with GC-electron impact ionization time-of-flight MS, GC-electron impact ionization/quadrupole MS, and LC-tandem MS analyses revealed that powdery mildew-susceptible grape berries were able to activate defensive mechanisms with the involvement of salicylic acid and jasmonates and to accumulate defense-associated metabolites (e.g. phenylpropanoids, fatty acids). The defensive strategies also indicated organ-specific responses, namely the activation of fatty acid biosynthesis. However, defense responses were not enough to restrict fungal growth. The fungal metabolic program during infection involves secretion of effectors related to effector-triggered susceptibility, carbohydrate-active enzymes and activation of sugar, fatty acid, and nitrogen uptake, and could be under epigenetic regulation. This study also identified potential metabolic biomarkers such as gallic, eicosanoic, and docosanoic acids and resveratrol, which can be used to monitor early stages of infection.

Vitis Species from the Southwestern United States Vary in Their Susceptibility to Powdery Mildew

The European grapevine (Vitis vinifera L.) has been cultivated in North America for about 500 years. One of the major limitations to its culture is the powdery mildew (PM) fungus, Erysiphe necator Schw. This study reports on the most extensive screening of Vitis species from the southwestern United States and northern Mexico for resistance to PM, testing 147 accessions of 13 Vitis species. In addition, Vitis vinifera cv. Carignane, a highly susceptible wine grape cultivar, was used as a reference to evaluate the effect of the inoculum 14 days postinoculation. Inoculation was done with a vacuum-operated settling tower using a broadly virulent isolate of E. necator, the C-strain. Resistant accessions (nine), moderately susceptible accessions (39), and highly susceptible accessions (99) were detected. The resistant accessions were then inoculated with an additional fungal isolate, e1-101, and they retained their resistance. Vitis species susceptibility was not associated with a North-South gradation, but Western species were more susceptible than Midwestern and Eastern species. All five of the V. monticola accessions were susceptible, as were the accessions of V. treleasei. The species V. acerifolia, V. candicans, V. cinerea, and V. × doaniana had significantly more resistant to moderately susceptible accessions compared with V. arizonica, V. berlandieri, V. californica, V. × champinii, V. girdiana, V. riparia, and V. rupestris, which had relatively more susceptible accessions than the other species. This research identified new sources of PM resistance in Vitis from the southwestern United States that could be incorporated into PM resistance breeding programs throughout the world.

High-Density Genetic Linkage Map Construction and White Rot Resistance Quantitative Trait Loci Mapping for Genus Vitis Based on Restriction Site-Associated DNA Sequencing

Grape white rot (Coniothyrium diplodiella) is a major fungal disease affecting grape yield and quality. Quantitative trait locus (QTL) analysis is an important method for studying important horticultural traits of grapevine. This study was conducted to construct a high-density map and conduct QTL mapping for grapevine white rot resistance. A mapping population with 177 genotypes was developed from interspecific hybridization of a white rot-resistant cultivar (Vitis vinifera × V. labrusca 'Zhuosexiang') and white rot-susceptible cultivar (V. vinifera 'Victoria'). Single-nucleotide polymorphism (SNP) markers were developed by restriction site-associated DNA sequencing. The female, male, and integrated maps contained 2,501, 4,110, and 6,249 SNP markers with average genetic distances of adjacent markers of 1.25, 0.77, and 0.50 cM, respectively. QTL mapping was conducted based on white rot resistance identification of 177 individuals in July and August of 2017 and 2018. Notably, one stable QTL related to white rot resistance was detected and located on linkage group LG14. The phenotypic variance ranged from 12.93 to 13.43%. An SNP marker (chr14_3929380), which cosegregated with white rot resistance, was discovered and shows potential for use in marker-assisted selection to generate new grapevine cultivars with resistance to white rot.

Search for donors of powdery mildew resistance genes among seedless and table grape varieties

Powdery mildew (Erysiphe necator) is one of the most common and economically significant diseases of grapes. Currently, the main method of controlling the disease is pesticide treatment. Breeding of resistant varieties is necessary to reduce chemical treatments. Currently, a number of grape resistance genes to powdery mildew and DNA markers for identification the allelic status of these genes are known. In a study to determine the presence of resistance loci Ren3 and Ren9, 25 genotypes of table grape varieties were analyzed, including 18 seedless varieties. DNA markers GF15-42, ScORGF15-02 were used to identify Ren3 gene, and CenGen6 – to identify Ren9 gene. DNA of cultivars Regent and Seyve Villard 12-375, which have resistance alleles, were used as positive controls. As a result of DNA marker analysis, it was determined that genotypes of table varieties Viking, Kodryanka, Moldova, Nadezhda AZOS, Original and seedless varieties Pamyati Smirnova, Kishmish Zaporozhskiy and Kishmish 342 carry loci of resistance to powdery mildew Ren3 and Ren9.

Discovery of the REN11 Locus From Vitis aestivalis for Stable Resistance to Grapevine Powdery Mildew in a Family Segregating for Several Unstable and Tissue-Specific Quantitative Resistance Loci

Race-specific resistance loci, whether having qualitative or quantitative effects, present plant-breeding challenges for phenotypic selection and deciding which loci to select or stack with other resistance loci for improved durability. Previously, resistance to grapevine powdery mildew (GPM, caused by Erysiphe necator) was predicted to be conferred by at least three race-specific loci in the mapping family B37-28 × C56-11 segregating for GPM resistance from Vitis aestivalis. In this study, 9 years of vineyard GPM disease severity ratings plus a greenhouse and laboratory assays were genetically mapped, using a rhAmpSeq core genome marker platform with 2,000 local haplotype markers. A new qualitative resistance locus, named REN11, on the chromosome (Chr) 15 was found to be effective in nearly all (11 of 12) vineyard environments on leaves, rachis, berries, and most of the time (7 of 12) stems. REN11 was independently validated in a pseudo-testcross with the grandparent source of resistance, "Tamiami." Five other loci significantly predicted GPM severity on leaves in only one or two environments, which could indicate race-specific resistance or their roles in different timepoints in epidemic progress. Loci on Chr 8 and 9 reproducibly predicted disease severity on stems but not on other tissues and had additive effects with REN11 on the stems. The rhAmpSeq local haplotype sequences published in this study for REN11 and Chr 8 and 9 stem quantitative trait locus (QTL) can be used directly for marker-assisted selection or converted to SNP assays. In screening for REN11 in a diversity panel of 20,651 vines representing the diversity of Vitis, this rhAmpSeq haplotype had a false positive rate of 0.034% or less. The effects of the other foliar resistance loci detected in this study seem too unstable for genetic improvement regardless of quantitative effect size, whether due to race specificity or other environmental variables.

Novel stable QTLs identification for berry quality traits based on high-density genetic linkage map construction in table grape

BACKGROUND

Aroma, berry firmness and berry shape are three main quality traits in table grape production, and also the important target traits in grapevine breeding. However, the information about their genetic mechanisms is limited, which results in low accuracy and efficiency of quality breeding in grapevine. Mapping and isolation of quantitative trait locus (QTLs) based on the construction of genetic linkage map is a powerful approach to decipher the genetic determinants of complex quantitative traits.

RESULTS

In the present work, a final integrated map consisting of 3411 SLAF markers on 19 linkage groups (LGs) with an average distance of 0.98 cM between adjacent markers was generated using the specific length amplified fragment sequencing (SLAF-seq) technique. A total of 9 significant stable QTLs for Muscat flavor, berry firmness and berry shape were identified on two linkage groups among the hybrids analyzed over three consecutive years from 2016 to 2018. Notably, new stable QTLs for berry firmness and berry shape were found on LG 8 respectively for the first time. Based on biological function and expression profiles of candidate genes in the major QTL regions, 3 genes (VIT_08s0007g00440, VIT_08s0040g02740 and VIT_08s0040g02350) related to berry firmness and 3 genes (VIT_08s0032g01110, VIT_08s0032g01150 and VIT_08s0105g00200) linked to berry shape were highlighted. Overexpression of VIT_08s0032g01110 in transgenic Arabidopsis plants caused the change of pod shape.

CONCLUSIONS

A new high-density genetic map with total 3411 markers was constructed with SLAF-seq technique, and thus enabled the detection of narrow interval QTLs for relevant traits in grapevine. VIT_08s0007g00440, VIT_08s0040g02740 and VIT_08s0040g02350 were found to be related to berry firmness, while VIT_08s0032g01110, VIT_08s0032g01150 and VIT_08s0105g00200 were linked to berry shape.

Genetic mapping and survey of powdery mildew resistance in the wild Central Asian ancestor of cultivated grapevines in Central Asia

Cultivated grapevines (Vitis vinifera) lack resistance to powdery mildew (PM) with few exceptions. Resistance to this pathogen within V. vinifera has been reported in earlier studies and identified as the Ren1 locus in two Central Asian table grape accessions. Other PM-resistant cultivated varieties and accessions of the wild ancestor V. vinifera subsp. sylvestris were soon identified raising questions regarding the origin of the resistance. In this study, F1 breeding populations were developed with a PM susceptible V. vinifera subsp. vinifera breeding line and a PM-resistant subsp. sylvestris accession. Genotyping was carried out with five Ren1 locus linked SSR markers. A PM resistance locus explaining up to 96% of the phenotypic variation was identified in the same genomic position, where the Ren1 locus was previously reported. New SSR marker alleles linked with the resistance locus were identified. We report results of PM resistance in multiple accessions of subsp. sylvestris collected as seed lots or cuttings from five countries in the Caucasus and Central Asia. A total of 20 females from 11 seed lots and 19 males from nine seed lots collected from Georgia, Armenia, and Azerbaijan were resistant to PM. Three male and one female plant collected as cuttings from Afghanistan and Iran were also resistant to PM. Allelic analysis of markers linked with the Ren1 locus in conjunction with disease evaluation data found a high diversity of allelic haplotypes, which are only possible via recombination events occurring over a long time period. Sequence analysis of two alleles of the SSR marker that cosegregates with the resistance found SNPs that were present in the wild progenitor and in cultivated forms. Variable levels of PM resistance among the tested accessions were also observed. These lines of evidence suggest that the powdery mildew fungus may have been present in Asia for a longer time than currently thought, giving the wild progenitor V. vinifera subsp. sylvestris time to coevolve with and develop resistance to this pathogen.

Characterization of genetic determinants of the resistance to phylloxera, Daktulosphaira vitifoliae, and the dagger nematode Xiphinema index from muscadine background

BACKGROUND

Muscadine (Muscadinia rotundifolia) is known as a resistance source to many pests and diseases in grapevine. The genetics of its resistance to two major grapevine pests, the phylloxera D. vitifoliae and the dagger nematode X. index, vector of the Grapevine fanleaf virus (GFLV), was investigated in a backcross progeny between the F1 resistant hybrid material VRH8771 (Vitis-Muscadinia) derived from the muscadine R source 'NC184-4' and V. vinifera cv. 'Cabernet-Sauvignon' (CS).

RESULTS

In this pseudo-testcross, parental maps were constructed using simple-sequence repeats markers and single nucleotide polymorphism markers from a GBS approach. For the VRH8771 map, 2271 SNP and 135 SSR markers were assembled, resulting in 19 linkage groups (LG) and an average distance between markers of 0.98 cM. Phylloxera resistance was assessed by monitoring root nodosity number in an in planta experiment and larval development in a root in vitro assay. Nematode resistance was studied using 10-12 month long tests for the selection of durable resistance and rating criteria based on nematode reproduction factor and gall index. A major QTL for phylloxera larval development, explaining more than 70% of the total variance and co-localizing with a QTL for nodosity number, was identified on LG 7 and designated RDV6. Additional QTLs were detected on LG 3 (RDV7) and LG 10 (RDV8), depending on the in planta or in vitro experiments, suggesting that various loci may influence or modulate nodosity formation and larval development. Using a Bulked Segregant Analysis approach and a proportion test, markers clustered in three regions on LG 9, LG 10 and LG 18 were shown to be associated to the nematode resistant phenotype. QTL analysis confirmed the results and QTLs were thus designated respectively XiR2, XiR3 and XiR4, although a LOD-score below the significant threshold value was obtained for the QTL on LG 18.

CONCLUSIONS

Based on a high-resolution linkage map and a segregating grapevine backcross progeny, the first QTLs for resistance to D. vitifoliae and to X. index were identified from a muscadine source. All together these results open the way to the development of marker-assisted selection in grapevine rootstock breeding programs based on muscadine derived resistance to phylloxera and to X. index in order to delay GFLV transmission.

Recent advances in biotechnological studies on wild grapevines as valuable resistance sources for smart viticulture

Cultivated grapevines, Vitis vinifera subsp. sativa, are thought to have been domesticated from wild populations of Vitis vinifera subsp. sylvestris in Central Asia. V. vinifera subsp. sativa is one of the most economically important fruit crops worldwide. Since cultivated grapevines are susceptible to multiple biotic and abiotic soil factors, they also need to be grafted on resistant rootstocks that are mostly developed though hybridization between American wild grapevine species (V. berlandieri, V. riparia, and V. rupestris). Therefore, wild grapevine species are essential genetic materials for viticulture to face biotic and abiotic stresses in both cultivar and rootstock parts. Actually, viticulture faces several environmental constraints that are further intensified by climate change. Recently, several reports on biotic and abiotic stresses-response in wild grapevines revealed accessions tolerant to different constraints. The emergence of advanced techniques such as omics technologies, marker-assisted selection (MAS), and functional analysis tools allowed a more detailed characterization of resistance mechanisms in these wild grapevines and suggest a number of species (V. rotundifolia, V. rupestris, V. riparia, V. berlandieri and V. amurensis) have untapped potential for new resistance traits including disease resistance loci and key tolerance genes. The present review reports on the importance of different biotechnological tools in exploring and examining wild grapevines tolerance mechanisms that can be employed to promote elite cultivated grapevines under climate change conditions.

Construction of a High-Density Genetic Map and Mapping of Firmness in Grapes (Vitis vinifera L.) Based on Whole-Genome Resequencing

Berry firmness is one of the most important quality traits in table grapes. The underlying molecular and genetic mechanisms for berry firmness remain unclear. We constructed a high-density genetic map based on whole-genome resequencing to identify loci associated with berry firmness. The genetic map had 19 linkage groups, including 1662 bin markers (26,039 SNPs), covering 1463.38 cM, and the average inter-marker distance was 0.88 cM. An analysis of berry firmness in the F1 population and both parents for three consecutive years revealed continuous variability in F1, with a distribution close to the normal distribution. Based on the genetic map and phenotypic data, three potentially significant quantitative trait loci (QTLs) related to berry firmness were identified by composite interval mapping. The contribution rate of each QTL ranged from 21.5% to 28.6%. We identified four candidate genes associated with grape firmness, which are related to endoglucanase, abscisic acid (ABA), and transcription factors. A qRT-PCR analysis revealed that the expression of abscisic-aldehyde oxidase-like gene (VIT_18s0041g02410) and endoglucanase 3 gene (VIT_18s0089g00210) in Muscat Hamburg was higher than in Crimson Seedless at the veraison stage, which was consistent with that of parent berry firmness. These results confirmed that VIT_18s0041g02410 and VIT_18s0089g00210 are candidate genes associated with berry firmness.

Identification of Selective Sweeps in the Domesticated Table and Wine Grape (Vitis vinifera L.)

Grapevine (Vitis vinifera) is one of the most important fruit species in the Classical Mediterranean world. It is thought to have been domesticated 6,000-8,000 years ago in the Near East. However, the domestication of its wild relative into wine grapes or table grapes remains largely unknown. In this study, we analyzed 30 table grapes, 30 wine grapes, 30 dual-purpose grape accessions, as well as 30 wild relatives (Vitis vinifera ssp. sylvestris). The phenotypic comparison showed striking differences in berry weight, acidity and the content of aroma. Based on a total of 7,522,958 single-nucleotide polymorphisms, we identified several significant selective sweep regions for table and wine grapes. Besides the well-known sex-determination locus on chromosome 2, the other four highest signals shared by table and wine grapes could not be linked to the known QTLs. The identification of these genomic regions under selection sweep may reveal agronomically important traits that have been selected during grape domestication. This information not only sheds light on the mechanisms of adaptions and diversification, but also guide the genetic improvement in breeding programs.

Emergent Ascomycetes in Viticulture: An Interdisciplinary Overview

The reduction of pesticide usage is a current imperative and the implementation of sustainable viticulture is an urgent necessity. A potential solution, which is being increasingly adopted, is offered by the use of grapevine cultivars resistant to its main pathogenic threats. This, however, has contributed to changes in defense strategies resulting in the occurrence of secondary diseases, which were previously controlled. Concomitantly, the ongoing climate crisis is contributing to destabilizing the increasingly dynamic viticultural context. In this review, we explore the available knowledge on three Ascomycetes which are considered emergent and causal agents of powdery mildew, black rot and anthracnose. We also aim to provide a survey on methods for phenotyping disease symptoms in fields, greenhouse and lab conditions, and for disease control underlying the insurgence of pathogen resistance to fungicide. Thus, we discuss fungal genetic variability, highlighting the usage and development of molecular markers and barcoding, coupled with genome sequencing. Moreover, we extensively report on the current knowledge available on grapevine-ascomycete interactions, as well as the mechanisms developed by the host to counteract the attack. Indeed, to better understand these resistance mechanisms, it is relevant to identify pathogen effectors which are involved in the infection process and how grapevine resistance genes function and impact the downstream cascade. Dealing with such a wealth of information on both pathogens and the host, the horizon is now represented by multidisciplinary approaches, combining traditional and innovative methods of cultivation. This will support the translation from theory to practice, in an attempt to understand biology very deeply and manage the spread of these Ascomycetes.

Candidate genes for grape white rot resistance based on SMRT and Illumina sequencing

BACKGROUND

White rot is one of the most dangerous fungal diseases and can considerably affect grape berry production and quality. However, few studies have focused on this disease, and thus, finding candidate white rot resistance genes is of great importance for breeding resistant grapevine cultivars. Based on field observations and indoor experiments, the cultivars "Victoria" and "Zhuosexiang" showed significant differences in white rot resistance. For understanding the molecular mechanisms behind it, different phenotypes of grapevine leaves were used for RNA sequencing via Illumina and single-molecule real-time (SMRT) sequencing technology.

RESULTS

A transcript library containing 53,906 reads, including known and novel transcripts, was constructed following the full-length transcriptome sequencing of the two grapevine cultivars. Genes involved in salicylic acid (SA) and jasmonic acid (JA) synthesis pathways showed different expression levels. Furthermore, four key transcription factors (TFs), NPR1, TGA4, Pti6, and MYC2, all involved in the SA and JA signal pathways were identified, and the expression profile revealed the different regulation of the pathogenesis related protein1 (PR1) resistance gene, as mediated by the four TFs.

CONCLUSIONS

Full-length transcript sequencing can substantially improve the accuracy and integrity of gene prediction and gene function research in grapevine. Our results contribute to identify candidate resistance genes and improve our understanding of the genes and regulatory mechanisms involved in grapevine resistance to white rot.

The cytological basis of powdery mildew resistance in wild Chinese Vitis species

The wild Chinese grapevines (Vitis spp.) show varying levels of resistance to powdery mildew caused by Erysiphe necator that is an economically important disease of cultivated grapevines (Vitis vinifera). However, little information is available regarding the cytological mechanisms of powdery mildew resistance in these wild relatives. Here, we studied the cytological responses of three wild Chinese grapevine accessions after they were infected with E. necator (En) NAFU1 in comparison to the susceptible V. vinifera cv. 'Thompson Seedless' grape. The hyphal growth and sporulation of En NAFU1 were significantly restricted in wild species compared to 'Thompson Seedless', which appears to be associated with early cell wall deposition at the attempt sites, encasement of haustoria, and hypersensitive response-like cell death of penetrated epidermal cells. Moreover, endogenous free salicylic acid (SA) was more abundant in wild Chinese Vitis species than in 'Thompson Seedless' under pathogen-free condition. During En NAFU1 colonization, SA conjugates accumulated higher in wild grapevines than in 'Thompson Seedless'. In addition, the species-specific expression patterns of defense-associated genes during En NAFU1 colonization indicated that mechanisms underlying powdery mildew resistance are divergent among different wild Chinese Vitis species. These results contribute to understanding of mechanisms underlying defense responses of wild Chinese Vitis species against powdery mildew.

Grape (Vitis vinifera) VvDOF3 functions as a transcription activator and enhances powdery mildew resistance

DOF proteins are plant-specific transcription factors that play vital roles in plant development and defense responses. However, DOFs have primarily been investigated in model plants, and fairly limited research has been performed on grape (Vitis vinifera). In this study, we isolated and characterized a C₂-C₂ zinc finger structural DOF gene, VvDOF3, from the grape cultivar Jingxiu. The VvDOF3 protein showed nuclear localization and transcriptional activation ability, indicating that it functions as a transcription factor. The VvDOF3 gene was rapidly induced by exogenous salicylic acid (SA), jasmonic acid (JA), and powdery mildew infection. Overexpression of VvDOF3 in Arabidopsis thaliana enhanced resistance to Golovinomyces cichoracearum. Expression of the SA-responsive defense-related gene PR1 and the concentration of SA were up-regulated in transgenic Arabidopsis plants overexpressing VvDOF3. Together, these data suggest that VvDOF3 functions as a transcription factor in grape and enhances powdery mildew resistance through the SA signaling pathway.

A High-Throughput Phenotyping System Using Machine Vision to Quantify Severity of Grapevine Powdery Mildew

Powdery mildews present specific challenges to phenotyping systems that are based on imaging. Having previously developed low-throughput, quantitative microscopy approaches for phenotyping resistance to Erysiphe necator on thousands of grape leaf disk samples for genetic analysis, here we developed automated imaging and analysis methods for E. necator severity on leaf disks. By pairing a 46-megapixel CMOS sensor camera, a long-working distance lens providing 3.5× magnification, X-Y sample positioning, and Z-axis focusing movement, the system captured 78% of the area of a 1-cm diameter leaf disk in 3 to 10 focus-stacked images within 13.5 to 26 seconds. Each image pixel represented 1.44 μm² of the leaf disk. A convolutional neural network (CNN) based on GoogLeNet determined the presence or absence of E. necator hyphae in approximately 800 subimages per leaf disk as an assessment of severity, with a training validation accuracy of 94.3%. For an independent image set the CNN was in agreement with human experts for 89.3% to 91.7% of subimages. This live-imaging approach was nondestructive, and a repeated measures time course of infection showed differentiation among susceptible, moderate, and resistant samples. Processing over one thousand samples per day with good accuracy, the system can assess host resistance, chemical or biological efficacy, or other phenotypic responses of grapevine to E. necator. In addition, new CNNs could be readily developed for phenotyping within diverse pathosystems or for diverse traits amenable to leaf disk assays.

R-Loci Arrangement Versus Downy and Powdery Mildew Resistance Level: A Vitis Hybrid Survey

For the viticulture of the future, it will be an essential prerequisite to manage grapevine diseases with fewer chemical inputs. The development and the deployment of novel mildew resistant varieties are considered one of the most promising strategies towards a sustainable viticulture. In this regard, a collection of 102 accessions derived from crossing Vitis hybrids with V. vinifera varieties was studied. In addition to the true-to-type analysis, an exhaustive genetic characterization was carried out at the 11 reliable mildew resistance (R) loci available in the literature to date. Our findings highlight the pyramiding of R-loci against downy mildew in 15.7% and against powdery mildew in 39.2% of the total accessions. The genetic analysis was coupled with a three-year evaluation of disease symptoms in an untreated field in order to assess the impact of the R-loci arrangement on the disease resistance degree at leaf and bunch level. Overall, our results strongly suggest that R-loci pyramiding does not necessarily mean to increase the overall disease resistance, but it guarantees the presence of further barriers in case of pathogens overcoming the first. Moreover, our survey allows the discovery of new mildew resistance sources useful for novel QTL identifications towards marker-assisted breeding.

Genetic diversity and parentage analysis of grape rootstocks

The maternal and paternal parentage of 36 rootstocks was determined and verified. The results of this study indicate that existing grape rootstocks are closely related to each other and have a narrow genetic background. Rootstocks are used to protect grapevines from biotic and abiotic stresses including phylloxera, nematodes, viruses, limestone-based soils, salinity and drought. The most important rootstocks were developed from three grape species between the 1890s and the 1930s in European breeding programs. In this report, we developed nuclear and chloroplast SSR fingerprint data from rootstock selections maintained in germplasm collections, compared them to develop a reference dataset, and carried out parentage analysis to resolve previously reported, and determine new, breeding records. We refined and updated the parentage of 26 rootstocks based on 21 nuclear and 14 chloroplast markers. Results indicate that 39% of the genetic background of analyzed rootstocks originated from only three accessions of three grape species: Vitis berlandieri cv. Rességuier 2, V. rupestris cv. du Lot and V. riparia cv. Gloire de Montpellier. Results determined that Rességuier 2 is the maternal parent for 14 commercial rootstocks, 9 of which are full-sibs with Gloire de Montpellier as the paternal parent. Similarly, du Lot is the paternal parent of nine rootstocks. The pedigree information for 28 rootstocks was determined or corrected in this study. The previously reported pedigree information for eight of the rootstocks was correct. The results found that the world's existing rootstocks have a narrow genetic base derived from only a few American grape species. Future rootstock breeding efforts should use a more diverse array of species to combat a changing climate and pest pressure.

Determination of downy and powdery mildew resistance of some Vitis spp

The Black Sea region of Turkey receives an annual rainfall of 2000-2500 mm and viticulture in the region depends on the rainfall limits significantly. In this study, the resistance of eighty different Vitis species and cultivars/genotypes to downy and powdery mildew was assessed using Marker Assisted Selection coupled with inoculation observations. Six Simple Sequence Repeats (SSR) and one Sequence Characterized Amplified Region (SCAR) markers were developed for different resistance loci (Run1, Rpv1, Ren1, Rpv3, Ren3) from different Vitis genetic resources. Eight of the cultivars/genotypes were characterised as resistant to downy mildew, seven were resistant to powdery mildew, and four were resistant to both diseases. These results, taken together with the disease inoculation observations, revealed ‘Köfteci Üzümü’ (Vitis labrusca) and ‘Giresun 3’ (Vitis labrusca) were the most resistant cultivars/genotypes.

Facing Climate Change: Biotechnology of Iconic Mediterranean Woody Crops

The Mediterranean basin is especially sensitive to the adverse outcomes of climate change and especially to variations in rainfall patterns and the incidence of extremely high temperatures. These two concurring adverse environmental conditions will surely have a detrimental effect on crop performance and productivity that will be particularly severe on woody crops such as citrus, olive and grapevine that define the backbone of traditional Mediterranean agriculture. These woody species have been traditionally selected for traits such as improved fruit yield and quality or alteration in harvesting periods, leaving out traits related to plant field performance. This is currently a crucial aspect due to the progressive and imminent effects of global climate change. Although complete genome sequence exists for sweet orange (Citrus sinensis) and clementine (Citrus clementina), olive tree (Olea europaea) and grapevine (Vitis vinifera), the development of biotechnological tools to improve stress tolerance still relies on the study of the available genetic resources including interspecific hybrids, naturally occurring (or induced) polyploids and wild relatives under field conditions. To this respect, post-genomic era studies including transcriptomics, metabolomics and proteomics provide a wide and unbiased view of plant physiology and biochemistry under adverse environmental conditions that, along with high-throughput phenotyping, could contribute to the characterization of plant genotypes exhibiting physiological and/or genetic traits that are correlated to abiotic stress tolerance. The ultimate goal of precision agriculture is to improve crop productivity, in terms of yield and quality, making a sustainable use of land and water resources under adverse environmental conditions using all available biotechnological tools and high-throughput phenotyping. This review focuses on the current state-of-the-art of biotechnological tools such as high throughput -omics and phenotyping on grapevine, citrus and olive and their contribution to plant breeding programs.

Introgression reshapes recombination distribution in grapevine interspecific hybrids

In grapevine interspecific hybrids, meiotic recombination is suppressed in homeologous regions and enhanced in homologous regions of recombined chromosomes, whereas crossover rate remains unchanged when chromosome pairs are entirely homeologous. Vitis rotundifolia, an American species related to the cultivated European grapevine Vitis vinifera, has a high level of resistance to several grapevine major diseases and is consequently a valuable resource for grape breeding. However, crosses between both species most often lead to very few poorly fertile hybrids. In this context, identifying genetic and genomic features that make cross-breeding between both species difficult is essential. To this end, three mapping populations were generated by pseudo-backcrosses using V. rotundifolia as the donor parent and several V. vinifera cultivars as the recurrent parents. Genotyping-by-sequencing was used to establish high-density genetic linkage maps and to determine the genetic composition of the chromosomes of each individual. A good collinearity of the SNP positions was observed between parental maps, confirming the synteny between both species, except on lower arm of chromosome 7. Interestingly, recombination rate in V. rotundifolia × V. vinifera interspecific hybrids depends on the length of the introgressed region. It is similar to grapevine for chromosome pairs entirely homeologous. Conversely, for chromosome pairs partly homeologous, recombination is suppressed in the homeologous regions, whereas it is enhanced in the homologous ones. This balance leads to the conservation of the total genetic length of each chromosome between V. vinifera and hybrid maps, whatever the backcross level and the proportion of homeologous region. Altogether, these results provide new insight to optimize the use of V. rotundifolia in grape breeding and, more generally, to improve the introgression of gene of interest from wild species related to crops.

Genome-wide characterization revealed role of NBS-LRR genes during powdery mildew infection in Vitis vinifera

NBS-LRR comprises a large class of disease resistance (R) proteins that play a widespread role in plant protection against pathogens. In grapevine, powdery mildew cause significant losses in its productivity and efforts are being directed towards finding of resistance loci or genes imparting resistance/tolerance against such fungal diseases. In the present study, we performed genome-wide analysis of NBS-LRR genes during PM infection in grapevine. We identified 18, 23, 12, 16, 10, 10, 9, 20 and 14 differentially expressed NBS-LRR genes in response to PM infection in seven partially PM-resistant (DVIT3351.27, Husseine, Karadzhandal, Khalchili, Late vavilov, O34-16, Sochal) and 2 PM-susceptible (Carignan and Thompson seedless) V. vinifera accessions. Further, the identified sequences were characterized based on chromosomal locations, physicochemical properties, gene structure and motif analysis, and functional annotation by Gene Ontology (GO) mapping. The NBS-LRR genes responsive to powdery mildew could potentially be exploited to improve resistance in grapes.

Cgr1, a ripe rot resistance QTL in Vitis amurensis 'Shuang Hong' grapevine

Ripe rot is a serious grapevine disease in Vitis L. and Muscadinia (Planch.) Small. However, resistance to this disease has been reported in some oriental Vitis species. To identify resistance-related Quantitative Trait Loci (QTLs) from the Chinese grape species V. amurensis, an F₁ population of V. vinifera 'Cabernet Sauvignon' × V. amurensis 'Shuang Hong' was used to map the ripe rot resistance loci expected in 'Shuang Hong' grape. A total of 7598 single nucleotide polymorphisms (SNPs) between the parents were identified in our previous study, and 934 SNPs were selected for genetic map construction. These SNPs are distributed across the 19 chromosomes covering a total of 1665.31 cM in length, with an average of 1.81 cM between markers. Ripe rot resistance phenotypes among the hybrids were evaluated in vitro using excised leaves for three consecutive years from 2016 to 2018; a continuous variation was found among the F₁ hybrids, and the Pearson correlation coefficients of the phenotypes scored in all three years were significant at the 0.01 level. Notably, the first QTL reported for resistance to grape ripe rot disease, named Cgr1, was identified on chromosome 14 of 'Shuang Hong' grapevine. Cgr1 could explain up to 19.90% of the phenotypic variance. In addition, a SNP named 'np19345' was identified as a molecular marker closely linked to the peak of Cgr1 and has the potential to be developed as a marker for the Cgr1 resistance haplotype.

Construction of a highly saturated Genetic Map for Vitis by Next-generation Restriction Site-associated DNA Sequencing

BACKGROUND

High-saturate molecular linkage maps are an important tool in studies on plant molecular biology and assisted breeding. Development of a large set of single nucleotide polymorphisms (SNPs) via next-generation sequencing (NGS)-based methods, restriction-site associated DNA sequencing (RAD-seq), and the generation of a highly saturated genetic map help improve fine mapping of quantitative trait loci (QTL).

RESULTS

We generated a highly saturated genetic map to identify significant traits in two elite grape cultivars and 176 F₁ plants. In total, 1,426,967 high-quality restriction site-associated DNA tags were detected; 51,365, 23,683, and 70,061 markers were assessed in 19 linkage groups (LGs) for the maternal, paternal, and integrated maps, respectively. Our map was highly saturated in terms of marker density and average "Gap ≤ 5 cM" percentage.

CONCLUSIONS

In this study, RAD-seq of 176 F₁ plants and their parents yielded 8,481,484 SNPs and 1,646,131 InDel markers, of which 65,229 and 4832, respectively, were used to construct a highly saturated genetic map for grapevine. This map is expected to facilitate genetic studies on grapevine, including an evaluation of grapevine and deciphering the genetic basis of economically and agronomically important traits. Our findings provide basic essential genetic data the grapevine genetic research community, which will lead to improvements in grapevine breeding.

Ectopic expression of Arabidopsis broad-spectrum resistance gene RPW8.2 improves the resistance to powdery mildew in grapevine (Vitis vinifera)

Powdery mildew is the most economically important disease of cultivated grapevines worldwide. Here, we report that the Arabidopsis broad-spectrum disease resistance gene RPW8.2 could improve resistance to powdery mildew in Vitis vinifera cv. Thompson Seedless. The RPW8.2-YFP fusion gene was stably expressed in grapevines from either the constitutive 35S promoter or the native promoter (NP) of RPW8.2. The grapevine shoots and plantlets transgenic for 35S::RPW8.2-YFP showed reduced rooting and reduced growth at later development stages in the absence of any pathogens. Infection tests with an adapted grapevine powdery mildew isolate En NAFU1 showed that hyphal growth and sporulation were significantly restricted in transgenic grapevines expressing either of the two constructs. The resistance appeared to be attributable to the ectopic expression of RPW8.2, and associated with the enhanced encasement of the haustorial complex (EHC) and onsite accumulation of H₂O₂. In addition, the RPW8.2-YFP fusion protein showed focal accumulation around the fungal penetration sites. Transcriptome analysis revealed that ectopic expression of RPW8.2 in grapevines not only significantly enhanced salicylic acid-dependent defense signaling, but also altered expression of other phytohormone-associated genes. Taken together, our results indicate that RPW8.2 could be utilized as a transgene for improving resistance against powdery mildew in grapevines.

Construction of a high-density genetic map for grape using specific length amplified fragment (SLAF) sequencing

Genetic maps are important tools in plant genomics and breeding. We report a large-scale discovery of single nucleotide polymorphisms (SNPs) using the specific length amplified fragment sequencing (SLAF-seq) technique for the construction of high-density genetic maps for two elite wine grape cultivars, ‘Chardonnay’ and ‘Beibinghong’, and their 130 F₁ plants. A total of 372.53 M paired-end reads were obtained after preprocessing. The average sequencing depth was 33.81 for ‘Chardonnay’ (the female parent), 48.20 for ‘Beibinghong’ (the male parent), and 12.66 for the F₁ offspring. We detected 202,349 high-quality SLAFs of which 144,972 were polymorphic; 10,042 SNPs were used to construct a genetic map that spanned 1,969.95 cM, with an average genetic distance of 0.23 cM between adjacent markers. This genetic map contains the largest molecular marker number of the grape maps so far reported. We thus demonstrate that SLAF-seq is a promising strategy for the construction of high-density genetic maps; the map that we report here is a good potential resource for QTL mapping of genes linked to major economic and agronomic traits, map-based cloning, and marker-assisted selection of grape.

RUN1 and REN1 Pyramiding in Grapevine (Vitis vinifera cv. Crimson Seedless) Displays an Improved Defense Response Leading to Enhanced Resistance to Powdery Mildew (Erysiphe necator)

Fungal pathogens are the cause of the most common diseases in grapevine and among them powdery mildew represents a major focus for disease management. Different strategies for introgression of resistance in grapevine are currently undertaken in breeding programs. For example, introgression of several resistance genes (R) from different sources for making it more durable and also strengthening the plant defense response. Taking this into account, we cross-pollinated P09-105/34, a grapevine plant carrying both RUN1 and REN1 pyramided loci of resistance to Erysiphe necator inherited from a pseudo-backcrossing scheme with Muscadinia rotundifolia and Vitis vinifera 'Dzhandzhal Kara,' respectively, with the susceptible commercial table grape cv. 'Crimson Seedless.' We developed RUN1REN1 resistant genotypes through conventional breeding and identified them by marker assisted selection. The characterization of defense response showed a highly effective defense mechanism against powdery mildew in these plants. Our results reveal that RUN1REN1 grapevine plants display a robust defense response against E. necator, leading to unsuccessful fungal establishment with low penetration rate and poor hypha development. This resistance mechanism includes reactive oxygen species production, callose accumulation, programmed cell death induction and mainly VvSTS36 and VvPEN1 gene activation. RUN1REN1 plants have a great potential as new table grape cultivars with durable complete resistance to E. necator, and are valuable germplasm to be included in grape breeding programs to continue pyramiding with other sources of resistance to grapevine diseases.

Genetic dissection of powdery mildew resistance in interspecific half-sib grapevine families using SNP-based maps

Quantitative trait locus (QTL) identification in perennial fruit crops is impeded largely by their lengthy generation time, resulting in costly and labor-intensive maintenance of breeding programs. In a grapevine (genus Vitis) breeding program, although experimental families are typically unreplicated, the genetic backgrounds may contain similar progenitors previously selected due to their contribution of favorable alleles. In this study, we investigated the utility of joint QTL identification provided by analyzing half-sib families. The genetic control of powdery mildew was studied using two half-sib F₁ families, namely GE0711/1009 (MN1264 × MN1214; N = 147) and GE1025 (MN1264 × MN1246; N = 125) with multiple species in their ancestry. Maternal genetic maps consisting of 1077 and 1641 single nucleotide polymorphism (SNP) markers, respectively, were constructed using a pseudo-testcross strategy. Ratings of field resistance to powdery mildew were obtained based on whole-plant evaluation of disease severity. This 2-year analysis uncovered two QTLs that were validated on a consensus map in these half-sib families with improved precision relative to the parental maps. Examination of haplotype combinations based on the two QTL regions identified strong association of haplotypes inherited from 'Seyval blanc', through MN1264, with powdery mildew resistance. This investigation also encompassed the use of microsatellite markers to establish a correlation between 206-bp (UDV-015b) and 357-bp (VViv67) fragment sizes with resistance-carrying haplotypes. Our work is one of the first reports in grapevine demonstrating the use of SNP-based maps and haplotypes for QTL identification and tagging of powdery mildew resistance in half-sib families.

A stilbene synthase allele from a Chinese wild grapevine confers resistance to powdery mildew by recruiting salicylic acid signalling for efficient defence

Stilbenes are central phytoalexins in Vitis, and induction of the key enzyme stilbene synthase (STS) is pivotal for disease resistance. Here, we address the potential for breeding resistance using an STS allele isolated from Chinese wild grapevine Vitis pseudoreticulata (VpSTS) by comparison with its homologue from Vitis vinifera cv. 'Carigane' (VvSTS). Although the coding regions of both alleles are very similar (>99% identity on the amino acid level), the promoter regions are significantly different. By expression in Arabidopsis as a heterologous system, we show that the allele from the wild Chinese grapevine can confer accumulation of stilbenes and resistance against the powdery mildew Golovinomyces cichoracearum, whereas the allele from the vinifera cultivar cannot. To dissect the upstream signalling driving the activation of this promoter, we used a dual-luciferase reporter system in a grapevine cell culture. We show elevated responsiveness of the promoter from the wild grape to salicylic acid (SA) and to the pathogen-associated molecular pattern (PAMP) flg22, equal induction of both alleles by jasmonic acid (JA), and a lack of response to the cell death-inducing elicitor Harpin. This elevated SA response of the VpSTS promoter depends on calcium influx, oxidative burst by RboH, mitogen-activated protein kinase (MAPK) signalling, and JA synthesis. We integrate the data in the context of a model where the resistance of V. pseudoreticulata is linked to a more efficient recruitment of SA signalling for phytoalexin synthesis.