Location: Crop Diseases, Pests and Genetics Research
2021 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
In support of Objective 1, evaluations continued on advanced table grape selections with two virtual showings of selections to interested stakeholders. Nine advanced selections and six commercial cultivars were cultured with best known practices for comparative evaluations in fruit quality characteristics and box yield. From planted seedling populations, six new advanced table grape selections were identified during 2020 that warrant placement in the advanced trial block for future evaluation. Propagation materials of the new selections have been collected to produce sufficient vines for establishment in the advanced trial block. Segregating populations for fruit quality traits including flowering time, berry shape, size, texture and color and bud break were evaluated. Genetic maps are being constructed for quantitative trait locus (QTL) analyses. A grape population segregating for powdery mildew and Botrytis resistance was evaluated for disease resistance to powdery (field) and gray mold (postharvest storage). A genetic map is being constructed to identify potential loci associated with resistance in a V. cinerea genetic background.
Hybridizations continue in both table grapes and raisins to develop durable resistances to both powdery mildew and Pierce’s disease in support of Objective 2. Reflex-flowered Run1Ren1Ren4 vines have been used as females in backcrosses with high quality table grapes and natural dry-on-vine raisin selections. Pollen from other perfect-flowered Run1Ren1Ren4 vines have been collected and shared with Vitis breeders in Minnesota and New York for use with hybrids having different combinations of powdery mildew resistance genes. Pollen from Run1Ren1Ren4 hybrids has also been used in hybridizations with powdery mildew resistant selections of V. amurensis, an as yet-to-be characterized powdery mildew resistance source. Relative to increasing durability of resistance to Pierce’s disease, hybridizations were made to combine the two different Pierce’s disease resistance sources. Pierce’s disease resistant vines with Vitis arizonica background were used as seed parents in hybridizations with Pierce’s disease resistant vines with a southeast U.S. background. Sources of Pierce’s Disease resistance from V. arizonica, southeast U.S. background 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. After four years of yield evaluation in the Almond Board of California-sponsored Regional Almond Variety Trials, the new self-fertile Yorizane cultivar has been released from the Parlier, California, breeding program. Recent hybridizations have yielded a new early-ripening self-fertile almond selection. While the new selection lacks perfect kernel quality, its early-ripening character makes it an attractive parent in the development of new self-fertile selections. Numerous backcrosses were performed during the 2021 bloom period between large-fruited apricots carrying the glabrous-skin gene (seed parent) and high quality glabrous-skinned 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.
Accomplishments
1. Self-fertile Yorizane almond. Eighty percent of the world’s almonds are grown in California with the majority of the 1.5 million acres being planted to self-infertile cultivars. The California almond industry desires new self-fertile cultivars to assist honeybees with nut set. ARS researchers in Parlier, California, developed the new self-fertile Yorizane cultivar in response to industry desires. The new cultivar has yielded well in trials throughout the San Joaquin Valley and has been rated highly in marketing potential and kernel appearance. The Yorizane release has been noted in the almond industry with dormant budwood being provided to six requesting tree nut nurseries for the development of mother trees.
2. Major source of resistance to Pierce’s Disease is resistant to multiple bacterial strains. Pierce’s Disease is a bacterial disease of grape causing loss of production. Breeding for resistance has focused on a single source in grape from Vitis arizonica. ARS Researchers in Parlier, California, tested the major source of resistance against a panel of seven different Xylella fastidiosa strains, the bacteria causing Pierce’s Disease. Little to no disease was observed in the resistant V. arizonica when challenged with each bacterial strain. This suggests that the currently used major source of resistance in grape breeding will be effective in multiple grape growing regions.
Review Publications
Bourguiba, H., Scotti, I., Sauvage, C., Zhebentvaeva, T., Ledbetter, C.A., Krska, B., Remay, A., D'Onofrio, C., Iketani, H., Christen, D., Krichen, L., Trifi-Farah, N., Liu, W., Roch, G., Audergon, J. 2020. Genetic structure of a worldwide germplasm collection of Prunus armeniaca L. reveals three major diffusion routes for the varieties issued from the species’ centre of origin. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2020.00638.
Zou, C., Karn, A., Reisch, B., Nguyen, A., Sun, Y., Bao, Y., Campbell, M.S., Church, D., Williams, S., Xu, X., Ledbetter, C.A., Patel, S., Fennell, A., Glaubitz, J., Clark, M., Ware, D., Londo, J.P., Sun, Q., Cadle Davidson, L.E. 2020. Haplotyping the Vitis collinear core genome with rhAmpSeq improves marker transferability in a diverse genus. Nature Communications. https://doi.org/10.1038/s41467-019-14280-1.
