Location: Crop Diseases, Pests and Genetics Research
2023 Annual Report
Objectives
The long-term goal of this project is development and introduction of new, high-quality and disease resistant cultivars of Prunus (almond and apricot) and Vitis (table grapes and raisins) that will sustain American agriculture and supply high quality, nutritious fruits and nuts to U.S. consumers and international markets. Further, the project will strive to identify molecular markers linked sufficiently close to fruit quality traits of interest such that marker-assisted selection will be possible in future breeding efforts. Specifically, during the next five years we will focus on the following objectives:
Objective 1: Enhance breeding efficiency for table grape fruit quality, and other priority traits, by identifying associated molecular markers, and through trials, to determine commercial acceptability of advanced table grape selections.
Sub-objective 1A: Develop segregating populations and map fruit quality traits related to flowering time, rachis architecture, and berry size.
Sub-objective 1B: Through trials, determine commercial acceptability of advanced table grape selections.
Sub-objective 1C: Identify sources of resistance and develop molecular markers associated with resistance to Botrytis cinerea.
Objective 2: Develop durable resistances to powdery mildew and Pierce’s disease in table grapes and natural dry-on-vine raisins.
Sub-objective 2A: Develop durable resistance to powdery mildew in table grapes and natural dry-on-vine raisins.
Sub-objective 2B: Identify sources of durable resistance to Pierce’s disease and determine the relative susceptibility of existing commercial cultivars.
Sub-objective 2C: Develop table grape and natural dry-on vine raisin cultivars with durable resistance to Pierce’s disease.
Objective 3: Develop, select, and evaluate new, high quality scions of Prunus, e.g., high yielding self-compatible almond and glabrous-skinned apricot.
Sub-objective 3A: Develop, select, and evaluate new high-yielding self-compatible almonds.
Sub-objective 3B: Develop, select, and evaluate new glabrous-skinned apricots.
Approach
Classical breeding has been used to create segregating populations in Prunus and Vitis where the expression of quantitative traits has been concentrated and newly available characters have been transferred into adapted germplasm. New segregating populations will be created in Vitis to develop molecular markers for fruit quality traits, rachis architecture, resistance to Botrytis, flowering time and berry size. Advanced table grape selections will be compared for production timing and fruit quality after cold storage with existing table grape cultivars through public fruit showings held during each ripening season. Commercially acceptable advanced table grape selections will be introduced as new cultivars through consensus evaluation with the table grape industry.
New powdery mildew resistance sources will be evaluated in established segregating populations, and resistant accessions will be backcrossed with high quality table grapes and natural dry on the vine raisins as molecular markers are being developed. These new resistance sources will be used along with other mapped PM resistance sources in hybridizations designed to stack the resistances for durability. Empirical screening of Vitis germplasm for reaction to Xylella fastidiosa will continue, and existing commercial table grape cultivars will be evaluated for their relative susceptibility to Pierce’s disease. Crosses will be conducted to stack Xf resistances from Vitis arizonica and southeast U.S. Vitis germplasm into hybrids with high product quality. Promising high quality accessions with will be evaluated for survival and productivity in regions with high Pierce’s disease pressure.
In Prunus, hybridizations will be performed to identify and select new high-yielding self-compatible almonds that are California-adapted and have Nonpareil-like kernel characteristics. Apricot populations will be developed through hybridization among glabrous-skinned accessions, and new glabrous apricots will be evaluated for fruit quality and productivity. Newly-available glabrous-skinned apricot accessions from Kyrgyzstan will be propagated when available from plant protective quarantine and used in hybridizations to assist in the glabrous-skinned apricot breeding effort.
Progress Report
This is the final report for project 2034-21220-007-000D, ‘Breeding Prunus and Vitis Scions for Improved Fruit Quality and Durable Pest Resistance’ that will be replaced with project 2034-21220-008-000D, ‘Breeding Prunus and Vitis to Improve Disease Resistance, Fruit Quality, and Climate Change Adaptation.’
This project had continued support from industry stakeholders to carry out hybridizations in table and raisin grapes to develop new varieties that perform better and have natural disease resistance to fungal and bacterial pathogens. However, a vector-transmitted virus impacted the progress of the project. Virus-infected grapevines (95 percent of the germplasm) were removed to protect the germplasm. Germplasm in four grapevine blocks was evaluated and hardwood cuttings were taken. Plants were propagated and are maintained in greenhouses until field blocks are prepared for new plantings. Grapevines maintained in the greenhouse will be tested for the presence of pathogenic viruses before being transplanted to the field.
In support of Objective 1, evaluations continued on advanced table grape selections. However, COVID restrictions hampered in-person evaluations and showings of grape clusters to industry stakeholders. Only two showings of selections were conducted to interested stakeholders. Six new table grape selections were identified that warrant placement in the advanced trial block for future evaluation. Due to infection by a vector-transmitted virus, all of the segregating populations developed and established for fruit quality traits including flowering time, berry shape, size, texture, color, and bud break were destroyed to protect the remaining grapevine germplasm collection in Parlier. Similarly, the grapevine population that segregated for development of resistance to Botrytis was destroyed. Virus infection disrupted the planting of the advance selection trial as well. Plant material was sent to Foundation Plant Services at the University of California, Davis, and Microparadox for disinfection after implementation of material transfer agreements. Virus-free grapevines of advance selections will be trialed in the new project 2034-21220-008-000D. A genetic map is being constructed to identify potential loci associated with resistance to powdery mildew in four genetic backgrounds (populations). The four populations were selected for computer vision phenotypic analysis to estimate powdery mildew infestation.
In support of Objective 2, for both table and raisin grapes, hybridizations were completed to develop lines that have more than one resistance locus and could provide durable resistance to powdery mildew and Pierce’s disease. Reflex-flowered vines with combination of Run1Ren1Ren4 loci were used as females in backcrosses with high quality table grapes and natural dry-on-vine raisin selections. Pollen from Run1Ren1Ren4 hybrids was also used in hybridizations with powdery mildew resistant selections of Vitis amurensis, where a new locus for powdery mildew resistance was identified and named Ren12. To increase the durability of resistance to Pierce’s disease, hybridizations were conducted to combine the two different Pierce’s disease resistance sources. Currently, resultant seeds from these hybridizations are stored in a cold room for future germinations, and seedlings will be planted in the next season. Multiple sources of Pierce’s disease resistance from V. arizonica and an interspecific hybrid V. caribae were evaluated for sensitivity to seven isolates of Xylella fastidiosa to test the durability of resistance.
Evaluation efforts continue in support of Objective 3 for the development of new self-fertile almonds and glabrous-skinned apricots. A self-fertile cultivar named Yorizane was released from the breeding program at Parlier, California, after four years of yield evaluation. Yield evaluations were conducted by the Almond Board of California-sponsored Regional Almond Variety Trials in which Yorizane was tested and compared with other Almond cultivars. Another early ripening self-fertile almond selection was identified from recent hybridizations. The new selection lacks perfect kernel quality; however, its early-ripening character makes it an attractive parent in the development of new self-fertile selections. During the 2021 fruit ripening season, several new high quality glabrous-skinned apricots were selected from segregating populations. Queries to plant protective quarantine during the early 2021 fruit season have indicated that the large-fruited Kyrgyzstan glabrous-skinned apricots are still in a juvenile stage of development and not yet ready for selection and propagation. New apricot cultivar CASTLECREST, tested previously as Y112-215-04 was released in 2022. CASTLECREST was released as a mid-season apricot suitable for fresh market production.
Accomplishments
1. Release of apricot variety Castlecrest. The California fresh fruit market desires a mid-season apricot suitable for fresh market production. ARS scientists at Parlier, California, selected a new cultivar among 24 siblings for excellent fruit quality in June 2009. Its pedigree can be traced through seven generations of apricot breeding in the central San Joaquin Valley of California. Trees exhibit intermediate vigor and have an upright growth habit. This variety can be easily maintained to provide an open center to enhance light interception by developing flower buds.
Review Publications
Massonnet, M., Riaz, S., Pap, D., Figueroa-Balderas, R., Walker, M.A., Cantu, D. 2022. 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. Frontiers in Plant Science. 13. Article 1096862. https://doi.org/10.3389/fpls.2022.1096862.
Xiao, H., Liu, Z., Wang, N., Long, Q., Cao, S., Huang, G., Liu, W., Peng, Y., Riaz, S., Walker, M.A., Gaut, B.S., Zhou, Y. 2023. Adaptive and maladaptive introgression in grapevine domestication. Proceedings of the National Academy of Sciences (PNAS). 120(24). Article e2222041120. https://doi.org/10.1073/pnas.2222041120.
Huerta-Acosta, K., Riaz, S., Tenscher, A., Walker, M.A. 2022. Genetic characterization of Pierce’s disease resistance in a Vitis arizonica/monticola wild grapevine. American Journal of Enology and Viticulture. 74(1). Article 0740003. https://doi.org/10.5344/ajev.2022.22021.
