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.

Selected genotypes with the genetic background of Vitis aestivalis and Vitis labrusca are resistant to Xiphinema index

The ectoparasitic nematode Xiphinema index transmits grapevine fanleaf virus (GFLV) during feeding on grapevine roots, causing fanleaf degeneration in the plant. Hence, resistance breeding is a key to develop novel rootstocks to overcome such threats. In the past years, various grapevine species were screened, and a few candidates with partial resistance were identified. Yet, they were hardly sufficient for viticulture due to many agronomical defects. To develop reliably resistant rootstocks applicable in viticulture, multiple Vitis spp. genotypes were analyzed using root inoculation with nematodes in glass vials as an early and easy evaluation test. Resistance levels were evaluated 35 days after inoculation based on nematode reproduction factors focusing on juveniles and eggs. Infection of grapevines with GFLV was analyzed after inoculation with viruliferous X. index. With this fast screening system, putative candidates with resistances against X. index have been identified for future breeding programs. Particularly, genotypes with the genetic background of V. aestivalis and V. labrusca were found to be nematode resistant.

Distinct responses of Vitis aestivalis ‘Norton’ and Vitis vinifera ‘Kishmish Vatkana’ to seven viruses revealed by small RNA sequencing

Grapevines are frequently infected by multiple viruses. Our previous study showed that ‘Norton’ grapevine (Vitis aestivalis) is resistant to grapevine vein clearing virus, a DNA virus in the family Caulimoviridae. To study the reaction of ‘Norton’ to RNA viruses, we transferred seven RNA viruses to ‘Norton’ from ‘Kishmish Vatkana’ (‘KV’) (Vitis vinifera) via graft-transmission. We profiled viral small RNAs (vsRNAs) of the seven viruses and compared viral titers in ‘Norton’ and ‘KV’. Total vsRNAs of grapevine leafroll-associated virus 1 (GLRaV-1), GLRaV-2, GLRaV-3, grapevine virus A (GVA) and grapevine Pinot gris virus (GPGV) were significantly less abundant in ‘Norton’ than in ‘KV’, but total vsRNAs of grapevine fleck virus (GFkV) were more abundant in ‘Norton’ than in ‘KV’. Total vsRNAs of grapevine rupestris stem pitting-associated virus (GRSPaV) were not different between ‘Norton’ and ‘KV’. Grafting direction of ‘Norton’ to ‘KV’ or ‘KV’ to ‘Norton’ did not affect the quantity of vsRNAs. The genome coverage of GLRaV-1, GLRaV-2, GLRaV-3 and GVA vsRNAs was lower in ‘Norton’ than ‘KV’. The 21-nt and 22-nt classes of vsRNAs were predominant for all seven viruses. Virus quantification by qPCR indicated that GLRaV-1 was undetectable in ‘Norton’, GLRaV-2, GLRaV-3, and GVA were less abundant in ‘Norton’, but GFkV was more abundant in ‘Norton’ than in ‘KV’. These results demonstrated that ‘Norton’ grapevine suppresses GLRaV-1, GLRaV-2, GLRaV-3, and GVA, but supports GFkV in comparison with ‘KV’. This study revealed new facets of complex molecular interactions between grapevines and multiple viruses.

North American Grape ‘Norton’ is Resistant to Grapevine Vein Clearing Virus

Grapevines (Vitis spp.) host viruses belonging to 17 families. Virus-associated diseases are a constant challenge to grape production. Genetic resources for breeding virus-resistant grape cultivars are scarce. ‘Norton’ is a hybrid grape of North American Vitis aestivalis and is resistant to powdery mildew and downy mildew. In this study, we assessed resistance of ‘Norton’ to grapevine vein clearing virus (GVCV), which is prevalent in native, wild Vitaceae and in vineyards in the Midwest region of the U.S. We did not detect GVCV in ‘Norton’ as either the scion or the rootstock up to 3 years after it was grafted with a GVCV-infected ‘Chardonel’ grapevine. Upon sequencing of small RNAs, we were able to assemble the GVCV genome from virus small RNAs in GVCV-infected ‘Chardonel’ scion or rootstock, but not from grafted ‘Norton’ scion and rootstock. This study unveils a new trait of ‘Norton’ that can be used in breeding GVCV-resistant grape cultivars, and to investigate genetic mechanisms of ‘Norton’ resistance to GVCV.

High density mapping and quantitative trait loci analysis for fungal diseases in vitis aestivalis-derived 'Norton' and breeding for low palmitic acid in glycine max

Vitis aestivalis-derived 'Norton', the official grape of the State of Missouri, is grown in many U.S. regions where V. vinifera production requires extensive pesticide use for fungal disease management. To identify genetic factors of resistance to fungal diseases, a breeding population was developed from a cross between 'Norton' and 'Cabernet Sauvignon' at the Missouri State Fruit Experiment Station, resulting in 182 progenies. Utilizing this population, 19 different chromosomes of Norton, Cabernet Sauvignon and consensus were constructed using molecular/DNA markers. Downy mildew disease infection was studied 10 days after inoculation in the given population using both visual and quantitative measures. This study allowed us to discover a factor on chromosome 18 that is responsible for downy mildew resistance. Markers associated with this factor can be used to select seedling in young stage in the process of development of new cultivars. A phenotypic difference was observed for Botrytis bunch rot resistance in the same population, which will be utilized to identify corresponding genes after further analysis. Fatty acid manipulation in soybean oil by altering oil composition is an important breeding objective in the US. Reduction in saturated fatty acid particularly palmitic acid is recommended to improve cardiovascular health. In this study, we were able to identify and confirm new lines that carry low palmitic acid levels.