BREEDING PIERCES DISEASE RESISTANT GRAPES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1013811
• Project No.: CA-D-VIT-7086-H
• Project Start Date: Oct 1, 2017
• Project End Date: Jun 29, 2021

Project Director
Walker, M.

Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671

Performing Department
Viticulture and Enology

Non Technical Summary
This project supports the mission of the Agricultural Experiment Station by addressing the Hatch Act area(s) of: plant and animal production, protection, and health; sustainable agricultureThe Pierce's Disease resistant winegrape breeding program has made rapid progress. Aggressive vine training and selection for precocious flowering has allowed us to reduce the seed-to-seed cycle to 2 years. The use of molecular markers to facilitate selection of PD resistant progeny as soon as the seeds germinate saves valuable time and resources. These two practices have greatly accelerated the breeding program and allowed us to produce four backcross generations with elite Vitis vinifera winegrape cultivars arriving at the 97% vinifera level in only 10 years. Without molecular breeding support, it could take 20-25 years to get to the same level of resistance and fruit quality. We have fully characterized the resistance locus from V. arizonica/candicans b43-17 and named it PdR1 (Pierce's disease resistance gene 1). We have and generated four backcross generations (BC4 - 97% vinifera). Our companion mapping/genetics project has also identified markers for a second resistant accession V. arizonica b40-14 and we are also working on developing markers for resistance from V. arizonica/girdiana b42-26. We are maintaining backcross 2 (BC2), first filial (F1) cross and backcross 1 (BC1) mapping populations from these two genetic resources to facilitate the research of our mapping/genetics companion project. We have identified 22 new resistant accessions that were collected from the southwestern United States (US) and different regions of Mexico. Many of these have very strong resistance and will be tested to verify that their resistance is different from b43-17. It is critical to exploit the resistance from these diverse genetic backgrounds to broaden the base of PD resistance winegrape breeding and allow stacking (combining) of multiple and different resistant sources into a single line to strengthen resistance. We will begin this process by testing small breeding populations. We will continuing to develop different resistance sources to the 97% vinifera level, advance those with the best fruit and wine quality, expand to small scale wine testing on campus, and advance the best to 100 vine commercial scale field and wine making tests prior to release.

Animal Health Component

0%

Research Effort Categories

Basic

20%

Applied

55%

Developmental

25%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
202	1131	1081	80%
212	4010	1081	20%

Knowledge Area
212 - Pathogens and Nematodes Affecting Plants; 202 - Plant Genetic Resources;

Subject Of Investigation
1131 - Wine grapes; 4010 - Bacteria;

Field Of Science
1081 - Breeding;

Keywords

grape breeding

pierce's disease

vitis arizonica

disease resistance

xylella fastidiosa

Goals / Objectives
The overall objective of this proposal is to develop advanced vinifera-based PD resistant winegrapes that combine resistance from different genetic backgrounds for use in PD "hot-spots" across California and the US. For this purpose, we will continue to screen promising selections at Davis and produce fruit for small-scale fermentations. The best selections from these trials will advance to commercial scale winemaking with grower/winery cooperators. In coming years, we will expand planting of the advanced vinifera-based selections with multiple vines each for small-scale wine evaluation. Our goal is to develop lines representing different PD resistance sources with diverse and elite vinifera backgrounds, stack different lines for durable field resistance, and continue to evaluate new resistant germplasm to optimize the breeding of PD resistant winegrapes.1. Identify unique sources of PD resistance with a focus on accessions collected from the southwestern United States and northern Mexico. Develop F1 and BC1 populations from the most promising new sources of resistance. Evaluate the inheritance of resistance and utilize populations from the most resistant sources to create mapping populations. 2. Provide support to the companion mapping/genetics program by establishing and maintaining mapping populations, and using the greenhouse screen to evaluate populations and selections for PD resistance.3. Develop advanced lines of PD resistant winegrapes from unique resistance sources through four backcross generations to elite V. vinifera cultivars. Evaluate and select on fruit quality traits such as color, tannin content, flavor, and productivity. Complete wine and fruit sensory analysis of advanced selections.4. Utilize marker-assisted selection (MAS) to stack (combine) different resistance loci from the BC4 generation with advanced selections containing PdR1. Screen for genotypes with combined resistances, to produce new PD resistant grapes with multiple sources of PD resistance and high quality fruit and wine.

Project Methods
We make crosses in the spring based on the results of our Xf testing from the previous year. This testing includes seedling populations from previous crosses and novel Xf resistance sources from newly characterized germplasm. We also test populations to study the reliability of markers we are developing and verify inheritance in populations from diverse genetic backgrounds. Green cuttings are used to produce five replicates of each seedling Xf resistance screening. Our screening methodology for Xf resistance under greenhouse conditions is well established (Fishleder 1999, Krivanek and Walker 2005, Krivanek et al. 2005b). It is based on the widely used needle inoculation technique of Hopkins (1980, 1984) and has been effectively in use for the past 15 years in our lab. We wait between 12 and 16 weeks post inoculation, depending upon growth rate and weather, before samples are taken for ELISA evaluation.Our aggressive training practices force about 50% of the seedlings in a given population to fruit in their second year. This fruit is evaluated for appropriate winegrape characters such as: color, juiciness, vinous flavors, appropriate berry size, skin and seed tannin maturity, and ripening dates. Resistant selections are advanced to field testing at UC Davis and selected North Coast vineyards with chronic PD pressure. We are planning to expand these test sites and include other PD hot spot areas to test PD resistant lines in natural environment under high PD pressure.Grape and wine analysis is preformed on approximately 30 promising new PD resistant genotypes each year. Standard analytical procedures (Ough and Amerine 1988; Zoecklein et al. 1990; Boulton et al. 1996; Winter et al. 2004) will be used. These include Brix, pH, TA, color, hue, phenolics as well as berry and wine sensory assessment. Small lots of wine will be produced from particularly promising PD resistant genotypes at the UCD campus winery. Micro-vinification winemaking procedures will be employed with particular attention given to capturing varietal character and minimizing oxidation. This micro-vinification at a scale of 1 to 20 L is intended for about 15 selections per year.

Progress 10/01/17 to 06/29/21

Outputs
Target Audience:This continuing grape breeding program is directed towards breeding Pierce's disease (PD) resistant winegrapes. The target audiences include grape researchers, breeders and geneticists across the US and increasingly internationally as the causal agent continues to spread. The primary product of this project will be PD resistant winegrape cultivars that compete with traditional winegrape varieties in terms of fruit and wine quality while possessing strong resistance to PD. The patents are pending on five selections (three reds and two whites), and they are being distributed by California grape nurseries. The research program also publishes genetic maps of PD resistance and details the use of linked markers in breeding. These papers are listed in earlier versions of this project. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Karla Acosta-Huerta completed her PhD on the resistance of Mexican Vitis species to PD. Several publications are expected from her studies, one of which was submitted to Theoretical and Applied Genetics. How have the results been disseminated to communities of interest?Progress on this breeding program was reported to funding agencies, the wine industry and to grape geneticists, breeders and viticulturists. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? We have screened through about 2,000 progeny from the 2009, 2010, and 2011 crosses that are 97% V. vinifera with the PdR1b resistance gene from V. arizonica b43-17. We select for fruit and vine quality and then move the best to greenhouse testing, where only those with the highest resistance to Xylella fastidiosa (Xf), after multiple greenhouse tests, are advanced to multi-vine wine testing at Davis and other test sites. To date we have identified two different PD resistance genes that exist on different chromosomes. These forms of PD resistance come from grape species native to Mexico and the southwestern United States. Because we were able to locate these resistance genes - PdR1 (Krivanek et al., 2006), and PdR2 (Riaz, et al., 2018). We have been able to use marker-assisted selection (MAS) to screen for the DNA markers linked with these PD resistance genes to greatly accelerating our breeding progress. We have evaluated many thousands of resistant seedlings for horticultural traits and fruit quality. The best of these were advanced to greenhouse testing, where only those with the strongest PD resistance after multiple greenhouse tests, were advanced to wine quality testing at Davis and at PD hot spots around California. Twenty advanced PdR1b selections have been sent to Foundation Plant Services (FPS) over the past seven winters to verify their virus-free status. Five of them have been patented and are available from certified grape nurseries. Four winegrape selections that have both PdR1 and PdR2 resistance were delivered to FPS in 2019 and 2020. This stacking of PD resistance genes should broaden the genetic base of resistance. Selections of other wild grape species are being studied and the best will be utilized in the PD resistance breeding program. We have commenced an effort to stack powdery mildew resistance from a wide range of Vitis species into our advanced selections. Three red wine grapes have been patented and released (a winegrape they are reminiscent of is in parentheses): Camminare noir (Petite Sirah, Paseante noir (Zinfandel), and Errante noir (Cabernet Sauvignon). Two white wine grapes have been patented and released: Ambulo blanc (Chardonnay) and Caminante blanc (Sauvignon blanc). Numerous tastings of these wines have rated them as indistinguishable from V. vinifera wine grapes and very high quality. Most importantly, they are highly resistant to PD and have passed many greenhouse-based tests and are symptomless after many years in very high PD pressure regions of the State and Country. 17 winegrapes and 3 rootstocks with strong resistance and very good quality have been certified or are in the process of certification at FPS. Larger scale wines are being made for final evaluations. This project has also made strong progress on the molecular genetics of PD resistance. These studies identified a dominant form of PD resistance termed PdR1 in the V. arizonica/candicans accession b43-17, which we mapped to chromosome (Ch) 14. Markers linked to PdR1 were used to breed PD resistant grapes. Over 400 accessions of Vitis species growing in the southern US and Mexico were surveyed to identify new sources of PD resistance, and 14 promising resistant accessions were identified that might be capable of broadening the genetic base of PD resistance. A limited mapping strategy utilizing markers from Ch 14 in conjunction with greenhouse screen data to determine if the PD resistance in these 14 accessions is different from the previously identified PdR1 locus. All 14 had PD resistance on Ch 14 yet were quite genetically diverse in other parts of the genome. Progress Over the past 5 years the project has: Analyzed over 400 wild grape accessions collected from Mexico and the southwest USA for resistance to Pierce's disease. Genetic maps and quantitative analysis were completed for a total of 15 wild grape accessions including b40-14, b41-13 and T03-16. The first two collected from Mexico and the latter collected from Texas. Genetic mapping (QTL) analysis identified PD resistance on chromosome (Ch) 14, that explained greater than 50% variation in three accessions. To date we have identified 13 accessions with strong PD resistance on chromosome (Ch) 14. The accession, b42-26, has small effect QTLs on four chromosomes, 8, 10, 14 and 17 with additive effect. Limited mapping strategy with phenotypic and genotypic data of Ch14 indicated that ANU67 is the only accession so far with PD resistance not linked to Ch14. Physical maps were completed for southwestern Vitis accessions b43-17 and b40-14 and sequence comparisons to the susceptible PN40024 and Cabernet Sauvignon genome sequences are preparing. Two of the candidate genes RGA14 (resistance gene analog) and 18 were sequenced and verified. Plants were transformed with each candidate resistance gene. Promising results were obtained with one RGA14 line that provided a better cane maturation index and lower ELISA readings. This finding agrees with results from sequencing of cDNA from b43-17, the original source of resistance. Results after transformed plants were inoculated with X. fastidiosa, showed the amplification of fragments that comprise sequences identical to RGA14 but different from RGA18. Two St. George RGA18 lines did not show tolerance. Co-transformations with both pCLB2301NK-14 and pCLB2301NK-18 have produced several lines of Thompson Seedless and Chardonnay that are growing in vitro and will be tested in 2021. We are also using a reverse genetic approach using CRISPR-Cas9 systems on b43-17 and U0505-01 to knock out candidate genes to expedite the process of identifying resistant candidate genes. Patents granted: Walker, M.A., A.C. Tenscher, S. Riaz and N. Romero. Pierce's disease resistant winegrape 'Camminare noir' 07355-075. PP32,929. Walker, M.A., A.C. Tenscher, S. Riaz and N. Romero. Pierce's disease resistant winegrape 'Paseante noir' 09331-047. PP33,039. Walker, M.A., A.C. Tenscher, S. Riaz and N. Romero. Pierce's disease resistant winegrape 'Errante noir' 09356-235. PP32,999. Walker, M.A., A.C. Tenscher, S. Riaz and N. Romero. Pierce's disease resistant winegrape 'Ambulo blanc' 09314-102. PP32,949. Walker, M.A., A.C. Tenscher, S. Riaz and N. Romero. Pierce's disease resistant winegrape 'Caminante blanc' 09338-016. PP33,015. Presentations June 2020 to June 2021 Walker, M.A.Sonoma Vit Tech Group. Grape breeding. June 18. Walker, M.A. Farm Call with Crop Care PD issues with Cain Cellars and Staglin, also checked on GRN plot with Bob Steinhauer, July 7. Walker, M.A. Laffort USA seminar. Grape Breeding talk, July 14. Walker, M.A. Interview for Dan Baron Podcast, July17. Walker, M.A. Farm call with Ashley Anderson, Spring Mtn PD and new varieties, August 8. Walker, M.A. Interview with Agostino Petron, PD breeding, Aug 11. Walker, M.A. PD wine tasting with Silverado Winery organized through Crop Care, Aug 21 Walker, M.A. "Office hours with Dave and Anita" talk on PD PM resistant wine grapes. Aug 25. Walker, M.A. Talk for Expo 2020 ... Can viticulture be sustainable without disease resistant varieties, Oct. 14. Walker, M.A. 2020. New PD resistant winegrapes from UCD interview with Elaine Corn, Ag Press, UC Davis, Jan. 8, 2020 Walker, M.A. Unified PD resistant Wine tasting with virtual tasting, and lecture, Jan. 28 Walker, M.A. USDA Parlier talk on "30 yrs. of grape breeding at UC Davis", Virtual talk, Feb. 16 Walker, M.A. On the Road Seminars from UC Davis, Kern County. PD resistant wine grapes are ready to plant. Mar. 16. Walker, M.A. Recent Advances Viticulture and Enology. Presentation, 30+ years of grape breeding and I'm just getting started! Apr. 8 Walker, M.A. RMI Forum - Walker/Waterhouse session. Breeding legacy, May 12. Walker, M.A. interview with Agostino Petroni PD breeding article, May 27

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Riaz S, Tenscher AC, Heinitz CC, Huerta-Acosta KG, Walker MA. Genetic analysis reveals an east-west divide within North American Vitis species that mirrors their resistance to Pierce's disease. PLoS One. 2020;15(12):e0243445. Published 2020 Dec 18. doi:10.1371/journal.pone.0243445
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Elaine A Backus, Holly J Shugart, Jose Gutierrez, Timothy A Ebert, M Andrew Walker, Field-Collected Glassy-Winged Sharpshooters (Hemiptera: Cicadellidae) Perform More Xylella fastidiosa-Inoculating Behaviors on Susceptible Vitis vinifera cv. Chardonnay Than on Resistant Vitis champinii Grapevines, Journal of Economic Entomology, Volume 114, Issue 5, October 2021, Pages 19912008, https://doi.org/10.1093/jee/toab141
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Riaz, S., CM Men�ndez, AC Tenscher, D Pap and MA Walker. 2020. Genetic mapping and survey of powdery mildew resistance in the wild Central Asian ancestor of cultivated grapevines in Central Asia. Horticultural Research 7:104
• Type: Journal Articles Status: Awaiting Publication Year Published: 2021 Citation: Riaz S, AC Tenscher, CC Heinitz, KG Huerta-Acosta, M A Walker. 2021. Genetic analysis reveals an east-west divide within North American Vitis species that mirrors their resistance to Pierces disease. PLOS ONE(In press).
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Andrew Walker, "Breeding Pirece's Disease Resistant Winegrapes", Proceedings of the 2021 Pierces Disease Research Symposium, CDFA, December 2021, Sacramento, CA
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Andrew Walker & Dario Cantu, "Molecular Breeding Support for the Development of Pierce's Disease Resistant Winegrapes", Proceedings of the 2021 Pierces Disease Research Symposium, CDFA, December 2021, Sacramento, CA

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:This continuing grape breeding program is directed towards breeding Pierce's disease (PD) resistant winegrapes. The target audiences include grape researchers, breeders and geneticists across the US and increasingly internationally as the causal agent continues to spread. The primary product of this project will be PD resistant winegrape cultivars that compete with traditional winegrape varieties in terms of fruit and wine quality while possessing strong resistance to PD. The patents are pending on five selections (three reds and two whites), and they are being distributed by California grape nurseries. The research program also publishes genetic maps of PD resistance and details the use of linked markers in breeding. These papers are listed in earlier versions of this project. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Karla Acosta-Huerta completed her PhD on the resistance of Mexican Vitis species to PD. Several publications are expected from her studies, one of which has been submitted to Theoretical and Applied Genetics. How have the results been disseminated to communities of interest?Progress on this breeding program is reported to funding agencies, the wine industry and to grape geneticists, breeders and viticulturists. What do you plan to do during the next reporting period to accomplish the goals?Transfer this breeding program to my successor.

Impacts
What was accomplished under these goals? We continue to address the long-term goals of this project: 1. Breed PD resistant winegrapes through backcross techniques using high quality V. vinifera winegrape cultivars and X. fastidiosa resistant selections and sources characterized from our previous efforts. 2. Continue the characterization of X. fastidiosa resistance and winegrape quality traits (color, tannin, ripening dates, flavor, productivity, etc.) in novel germplasm sources, in our breeding populations, and in our genetic mapping populations. 3. Understand the genetic control of PD resistance and characterize resistance in other grape species backgrounds to allow the stacking of different resistance genes to enable broad and durable resistance Breeding Pierce's disease (PD) resistant winegrapes continues to advance accelerated by aggressive vine training and selection for precocious flowering resulting in a seed-to-seed cycle of two years. To further expedite breeding progress, we use marker-assisted selection (MAS) for PD resistance genes to select resistant progeny as soon as seeds germinate. These two practices have allowed us to produce four backcross generations with elite Vitis vinifera winegrape cultivars in 10 years. We have screened through about 2,000 progeny from the 2009, 2010, and 2011 crosses that are 97% V. vinifera with the PdR1b resistance gene from V. arizonica b43-17. We select for fruit and vine quality and then move the best to greenhouse testing, where only those with the highest resistance to Xylella fastidiosa (Xf), after multiple greenhouse tests, are advanced to multi-vine wine testing at Davis and other test sites. The best of these have been advanced to field testing with commercial-scale wine production, the first of which was planted in Napa in June 2013. To date 20 scion and three PD resistant rootstocks based on PdR1b have been advanced to FPS for certification. Five of these selections have patents pending. Licenses have been granted to certified nurseries. We have mapped an alternative form of PD resistance from a different form of V. arizonica collected in Baja California - PdR2 which resides on Chromosome 8. We are now combining (stacking) PdR1b with PdR2 PD resistance have advanced these lines to the 96% V. vinifera level using MAS to confirm the presence of the two forms of resistance. Other forms of V. arizonica are being studied and we will combine multiple resistance sources to ensure durable resistance. This spring, the first three scion selections that employ both PdR1 and PdR2 resistance were delivered to FPS. Pierce's disease resistance from V. shuttleworthii and BD5-117 has also being pursued but progress has been limited by their complex multigenic resistance and the absence of associated genetic markers. Very small-scale wines from 94% and 97% V. vinifera PdR1b selections have been very good and have been received well at public tastings in Sacramento (California Association of Winegrape Growers; CAWG) and Santa Rosa (Sonoma Winegrape Commission), Napa Valley (Napa Valley Grape Growers and Winemakers Associations), Temecula (Temecula Valley Winegrape Growers and Vintners), Healdsburg (Dry Creek Valley and Sonoma Grape Growers and Winemakers), at last year's Unified Symposium and at UC Davis.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Riaz, S., CM Men�ndez, AC Tenscher, D. Pap and MA Walker. 2020. Genetic mapping and survey of powdery mildew resistance in the wild Central Asian ancestor of cultivated grapevines in Central Asia. Horticultural Research 7:104
• Type: Journal Articles Status: Accepted Year Published: 2020 Citation: Adam R. Zeilinger, A.R., C. Wallis, D. Beal, A. Sicard, A. Walker, R.P.P. Almeida. 2020. Non-linear dynamics of vector transmission of a plant pathogen: a test of theory and application to disease management. Ecosphere

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:This continuing grape breeding program is directed towards breeding Pierce's disease (PD) resistant winegrapes. The target audiences include grape researchers, breeders and geneticists across the US and increasingly internationally as the causal agent continues to spread. The primary product of this project will be PD resistant winegrape cultivars that compete with traditional winegrape varieties in terms of fruit and wine quality while possessing strong resistance to PD. The patents are pending on five selections (three reds and two whites), and they are being distributed by California grape nurseries. The research program also publishes genetic maps of PD resistance and details the use of linked markers in breeding. These papers are listed in earlier versions of this project. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Karla Acosta-Huerta is completing her PhD over the next year on the resistance of Mexican Vitis species to PD. How have the results been disseminated to communities of interest?Progress on this breeding program is reported to funding agencies, the wine industry and to grape geneticists, breeders and viticulturists. What do you plan to do during the next reporting period to accomplish the goals?This breeding program continues and is focused on combining multiple sources of PD resistance and incorporating resistance to powdery mildew into our advanced selections. We also continue to evaluate advanced selections for possible release.

Impacts
What was accomplished under these goals? We continue to address the long-term goals of this project: 1. Breed PD resistant winegrapes through backcross techniques using high quality V. vinifera winegrape cultivars and X. fastidiosa resistant selections and sources characterized from our previous efforts. 2. Continue the characterization of X. fastidiosa resistance and winegrape quality traits (color, tannin, ripening dates, flavor, productivity, etc.) in novel germplasm sources, in our breeding populations, and in our genetic mapping populations. 3. Understand the genetic control of PD resistance and characterize resistance in other grape species backgrounds to allow the stacking of different resistance genes to enable broad and durable resistance. We continue to address the long-term goals of this project: 1. Breed PD resistant winegrapes through backcross techniques using high quality V. vinifera winegrape cultivars and X. fastidiosa resistant selections and sources characterized from our previous efforts. 2. Continue the characterization of X. fastidiosa resistance and winegrape quality traits (color, tannin, ripening dates, flavor, productivity, etc.) in novel germplasm sources, in our breeding populations, and in our genetic mapping populations. 3. Understand the genetic control of PD resistance and characterize resistance in other grape species backgrounds to allow the stacking of different resistance genes to enable broad and durable resistance Breeding Pierce's disease (PD) resistant winegrapes continues to advance accelerated by aggressive vine training and selection for precocious flowering resulting in a seed-to-seed cycle of two years. To further expedite breeding progress, we use marker-assisted selection (MAS) for PD resistance genes to select resistant progeny as soon as seeds germinate. These two practices have allowed us to produce four backcross generations with elite Vitis vinifera winegrape cultivars in 10 years. We have screened through about 2,000 progeny from the 2009, 2010, and 2011 crosses that are 97% V. vinifera with the PdR1b resistance gene from V. arizonica b43-17. We select for fruit and vine quality and then move the best to greenhouse testing, where only those with the highest resistance to Xylella fastidiosa (Xf), after multiple greenhouse tests, are advanced to multi-vine wine testing at Davis and other test sites. The best of these have been advanced to field testing with commercial-scale wine production, the first of which was planted in Napa in June 2013. To date 20 scion and three PD resistant rootstocks based on PdR1b have been advanced to FPS for certification. Five of these selections have patents pending. Licenses have been granted to certified nurseries. We have mapped an alternative form of PD resistance from a different form of V. arizonica collected in Baja California - PdR2 which resides on Chromosome 8. We are now combining (stacking) PdR1b with PdR2 PD resistance have advanced these lines to the 96% V. vinifera level using MAS to confirm the presence of the two forms of resistance. Other forms of V. arizonica are being studied and we will combine multiple resistance sources to ensure durable resistance. This spring, the first three scion selections that employ both PdR1 and PdR2 resistance were delivered to FPS. Pierce's disease resistance from V. shuttleworthii and BD5-117 has also being pursued but progress has been limited by their complex multigenic resistance and the absence of associated genetic markers. Very small-scale wines from 94% and 97% V. vinifera PdR1b selections have been very good and have been received well at public tastings in Sacramento (California Association of Winegrape Growers; CAWG) and Santa Rosa (Sonoma Winegrape Commission), Napa Valley (Napa Valley Grape Growers and Winemakers Associations), Temecula (Temecula Valley Winegrape Growers and Vintners), Healdsburg (Dry Creek Valley and Sonoma Grape Growers and Winemakers), at last year's Unified Symposium and at UC Davis.

Publications

• Type: Conference Papers and Presentations Status: Accepted Year Published: 2019 Citation: Walker, A., A. Tenscher, S. Riaz, C. Ag�ero, R. Hu and N. Romero. 2019. PD resistant winegrape breeding program update. Proceedings of the 2018 PD/GWSS Symposium, Dec. 2019
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2019 Citation: Walker, M.A., D. Cantu, S. Riaz and C. Ag�ero. 2019. Molecular breeding support for the development of Pierces disease resistant winegrapes. Proceedings of the 2018 PD/GWSS Symposium, Dec. 2019
• Type: Book Chapters Status: Accepted Year Published: 2019 Citation: Walker MA, Heinitz CC, Riaz S and Uretsky J. 2019. Grape taxonomy and germplasm. In, Cantu D and Walker MA (Eds) The Grape Genome (Compendium of Plant Genomes) pp. 25  38.

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:This continuing grape breeding program is directed towards breeding Pierce's disease (PD) resistant winegrapes. The target audiences include grape researchers, breeders and geneticists across the US and increasingly internationally as the causal agent continues to spread. The primary product of this project will be PD resistant winegrape cultivars that compete with traditional winegrape varieties in terms of fruit and wine quality while possessing strong resistance to PD. The first five selections (three reds and two whites) are currently on pre-release to California grape nurseries to prepare for commercial distribution after patent and release by UC Davis. The research program also publishes genetic maps of PD resistance and details the use of linked markers in breeding. These papers are listed in earlier versions of this project. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Karla Acosta-Huerta is completing her PhD over the next year on the resistance of Mexican Vitis species to PD. How have the results been disseminated to communities of interest?Progress on this breeding program is reported to funding agencies, the wine industry and to grape geneticists, breeders and viticulturists. What do you plan to do during the next reporting period to accomplish the goals?Continue the PD breeding program objectives.

Impacts
What was accomplished under these goals? 1. Breed PD resistant winegrapes through backcross techniques using high quality V. vinifera winegrape cultivars and X. fastidiosa resistant selections and sources characterized from our previous efforts. 2. Continue the characterization of X. fastidiosa resistance and winegrape quality traits (color, tannin, ripening dates, flavor, productivity, etc.) in novel germplasm sources, in our breeding populations, and in our genetic mapping populations. 3. Understand the genetic control of PD resistance and characterize resistance in other grape species backgrounds to allow the stacking of different resistance genes to enable broad and durable resistance Breeding Pierce's disease (PD) resistant winegrapes continues to advance - accelerated by aggressive vine training and selection for precocious flowering resulting in a seed-to-seed cycle of two years. To further expedite breeding progress, we are using marker-assisted selection (MAS) for PD resistance genes to select resistant progeny as soon as seeds germinate. These two practices have allowed us to produce four backcross generations with elite Vitis vinifera winegrape cultivars in 10 years. We have screened through about 2,000 progeny from the 2009, 2010, and 2011 crosses that are 97% V. vinifera with the PdR1b resistance gene from V. arizonica b43-17. We select for fruit and vine quality and then move the best to greenhouse testing, where only those with the highest resistance to Xylella fastidiosa, after multiple greenhouse tests, are advanced to multi-vine wine testing at Davis and other test sites. The best of these have been advanced to field testing with commercial-scale wine production, the first of which was planted in Napa in June 2013. To date 20 scion and three PD resistant rootstocks have been advanced to FPS for certification. Five of these selections are now in pre-release to nurseries. Stacking of PdR1b with PD resistance from b42-26 (an alternative form of PD resistance controlled by multiple genes) has been advanced to the 96% V. vinifera level using MAS to confirm the presence of PdR1 as well as the recently discovered (see companion report) PD resistance locus on chromosome (Ch) 8 from b42-26, PdR2. Other forms of V. arizonica are being studied and the resistance of some will be genetically mapped for future efforts to combine multiple resistance sources and ensure durable resistance. Pierce's disease resistance from V. shuttleworthii and BD5-117 are also being pursued but progress is limited by their multigenic resistance and the absence of associated genetic markers. Very small-scale wines from 94% and 97% V. vinifera PdR1b selections have been very good and have been received well at public tastings in Sacramento (California Association of Winegrape Growers; CAWG) and Santa Rosa (Sonoma Winegrape Commission), Napa Valley (Napa Valley Grape Growers and Winemakers Associations), Temecula (Temecula Valley Winegrape Growers and Vintners), Healdsburg (Dry Creek Valley and Sonoma Grape Growers and Winemakers) and UC Davis.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Walker, A., A. Tenscher, S. Riaz, C. Ag�ero, R. Hu and N. Romero. 2018. PD resistant winegrape breeding program update. Proceedings of the 2018 PD/GWSS Symposium, San Diego, CA Dec. 2018
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Walker, M.A., S. Riaz and C. Ag�ero. 2018. Molecular breeding support for the development of Pierces disease resistant winegrapes. Proceedings of the 2018 PD/GWSS Symposium, San Diego, CA Dec. 2018
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Riaz S, Huerta-Acosta K, Tenscher AC, Walker MA (2018) Genetic characterization of Vitis germplasm collected from the southwestern US and Mexico to expedite Pierces disease resistance breeding. Theoretical and Applied Genetics 131: 1589-1602
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Vinifera hybrids and resistance to Pierces Disease. Annual meeting of the American Society for Enology and Viticulture-East, Charlottesville, VA July 11, 2017
• Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Controlling Pierces disease with molecular and classical breeding. European Conference on Xylella fastidiosa: Finding Answers to a Global Problem, Mallorca, Spain, November 2017
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Breeding PD resistant winegrapes  Tasting. Annual Meeting of the Georgia wine grape growers. Braselton, GA, Jan. 24, 2018