GENETIC IMPROVEMENT OF SOUR CHERRY AND CHERRY ROOTSTOCKS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1019472
• Project Start Date: Jul 1, 2019
• Project End Date: Sep 30, 2021
• Program Code: [(N/A)]- (N/A)

Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824

Performing Department
Horticulture

Non Technical Summary
The sour and sweet cherry industries are important contributors to Michigan's fruit production. To remain profitable in a global economy, the Michigan cherry industries must produce excellent quality fruit and mitigate risks due to diseases, pests and climatic stresses. The Michigan sour cherry industry, which represents approximately 70 percent of the U.S. production, is essentially a monoculture of the 400 year-old cultivar, 'Montmorency'. Unfortunately this provides an ideal environment for extensive crop losses due to unfavorable weather conditions and insect and disease threats. This was realized in 2002 and 2012 when floral spring freeze damage resulted in near complete crop losses. In the last five years, a new invasive insect, spotted winged Drosophila (SWD), has moved into Michigan with a devastating impact on the sour cherry industry. Female SWD lay eggs in the cherry fruit and the larvae can grow quickly, with up to 11 generations in a season, causing producers to need to spray pesticide as often as once a week. Because insect pressure and pesticide costs increase exponentially as the season progresses, there is intense interest in the development of sour cherry cultivars that ripen significantly ahead of 'Montmorency'. For diseases, the most important threat is cherry leaf spot as failure to control the causal fungus results in early defoliation leading to poor fruit quality and loss of winter hardiness. Chemical controls are costly, management can be challenging depending upon weather conditions and potential regulatory changes threaten use of certain classes of controlling chemicals. Fortunately sour cherry selections exist that are being used as parents to donate late bloom time, early maturity time and cherry leaf spot tolerance with the goal of combining these risk-mitigating traits with productivity and superior fruit quality.A second disease threat to the Michigan sweet and sour cherry industries is the soil-borne root rot fungus, Armillaria. Orchards infected with Armillaria have a gradual tree loss until the orchard is prematurely abandoned and removed. Because Armillaria is persistent in the soil and there are no cultural practices to manage the disease, infected orchard sites can no longer be used for cherry production, and frequently the land is sold for development. No resistant cherry rootstocks are available; however, tolerance is present in plum species. Therefore crosses are being attempted between cherry and plum to develop Armillaria tolerant rootstocks that are graft compatible with sweet and sour cherry.All sour cherry and the majority of sweet cherry trees in Michigan are on standard size rootstocks, with trees only coming into commercial production by years five to six. Recently there is interest in using dwarfing precocious rootstocks to enable 'Montmorency' trees to be planted at high densities and harvested in year three with an over-the-row harvester. Precocious, dwarfing rootstocks also allow fresh market sweet cherry growers to adopt high efficiency orchards systems and enhance profitability through earlier and increased yields, higher quality fruit, and reduced unit cost of production. Currently five Michigan State University cherry rootstocks that induce scion dwarfing and precocity have been released and they are currently being tested for their ability to increase the profitability of sweet and sour cherry production.Both the scion and rootstock breeding programs will be more efficient and effective using knowledge of the genetic control of important breeding trait targets. The availability of genetic maps and whole genome sequences has led to a rapid increase in the pace of genetic discovery. As genetic discoveries are made, they will be translated into breeding application. This includes using DNA-based knowledge to choose breeding parents, design crosses, and pre-select seedlings for field planting thereby culling those predicted to be undesirable.

Animal Health Component

80%

Research Effort Categories

Basic

20%

Applied

80%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
201	1112	1081	100%

Knowledge Area
201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
1112 - Cherry;

Field Of Science
1081 - Breeding;

Keywords

fruit breeding

cherry

disease resistance

rootstocks

Goals / Objectives
The overall goal is to develop new commercial sour cherry cultivars and rootstocks that increase industry profitability and sustainability. Specific goals are to: (1) Develop commercial sour cherry cultivars for Michigan and areas of similar climate while maintaining acceptable yields through improving fruit quality, cherry leaf spot resistance and spring frost avoidance. (2) Develop new cherry rootstocks that are tolerant to Armillaria and/or promote precocious scion flowering and dwarfing. (3) Discover and utilize new genetic knowledge to enhance the effectiveness of the MSU breeding programs.

Project Methods
SOUR CHERRY BREEDING: The breeding program consists of five activities: (1) germplasm collection, (2) hybridization, (3) seedling evaluation {pest and stress resistance, productivity, and fruit quality}, (4) advanced testing, and (5) cultivar release. The first stage, germplasm collection, was completed in 1998 with an exchange trip to Russia. Hybridizations have been made each spring and will continue using pollen from superior individuals identified in the breeding program. The resulting seedlings will be grown in a greenhouse at MSU Campus. Those families predicted to be segregating for self-in/compatibility and dark flesh color will be subject to DNA testing to identify undesirable individuals. Those individuals predicted to have the undesired trait will be discarded prior to field planting at MSU's Clarksville Research Center. Seedlings predicted to be especially useful due to their combination of alleles will be budded on precocious rootstocks to accelerate flowering and fruiting. Additional DNA tests for high priority traits will also be implemented as they become available.Seedlings planted in the field will be evaluated for numerous horticultural traits including: bloom date, harvest date, fruiting habit, and 11 fresh and 5 frozen fruit quality characteristics. In years with particularly high disease pressure or abiotic stress, the seedlings will be evaluated for their field resistance. Superior selections will be propagated and planted at 5 test sites in Michigan. Upon acceptable performance in these sites, 15 trees each will be propagated and planted at 6 second test evaluation sites in Michigan. These test sites will provide additional locations to observe these selections plus sufficient trees for yield data, mechanical harvesting and fruit for pilot processing trials. Once a selection has performed well in the disease screen and second test sites, it will be considered as a candidate for cultivar release.To assist in the advanced testing and to provide input for commercialization, a Sour Cherry Breeding Advisory Committee of six Michigan growers and processors was formed that meets annually. At this meeting, A. Iezzoni and the Advisory Committee review the progress and plans in the breeding program and sample fruit of the advanced selections. Suggested changes are implemented in the next growing season.BREEDING ARMILLARIA RESISTANT CHERRY ROOTSTOCK: Crosses between cherry and plum accessions from the National Clonal Germplasm repository that have exhibited in vitro tolerance to Armillaria are being undertaken. Any seed that is obtained will be germinated in vitro due to the high value of the hybrids. In addition, representatives of cherry species growing on Armillaria infected sites in the cherry orchard regions of Michigan will be identified, and the seed will be collected. The resulting seedlings from the crosses and collections will also be germinated in vitro to enable early screening for Armillaria. Any promising seedlings will be increased via cuttings or meristem cultivar to provide plants for evaluation for tree survival and health in Armilaria infected sites.BREEDING DWARFING PRECOCIOUS CHERRY ROOTSTOCKS: The suitability of the five MSU cherry rootstocks to enable an over-the-row production system are being evaluated in existing trials at MSU's Northwest Horticultural Research Center and grower trials planted in Michigan. Yield/trunk cross-sectional area will be recorded from trees in these trials along with fruit quality parameters (size, firmness, and soluble solids). The suitability of the MSU cherry rootstocks to enable a pedestrian sweet cherry orchard system are also being evaluated in trials planted in Washington and Oregon and as part of the NC140 sweet and sour cherry trials, led by NC140 project participants. In both the sour and sweet cherry trials, the control rootstocks include individuals from the Gisela® series. Results will be compiled yearly to assess whether any of the five MSU cherry rootstocks continue to have promise for high density orchard systems. Trees on the MSU cherry rootstocks are already available from licensed nurseries in the U.S. Therefore, if any of the MSU rootstocks are shown to have commercial utility, there will be no extra lag time for producers to obtained virus-certified trees on the MSU rootstocks.CHERRY GENETICS:Discovery of major loci and desirable alleles controlling horticulturally important traits: Progeny populations segregating for critical fruit quality traits (fruit firmness, shape and size; pit freestone/clingstone and shape), and CLS tolerance are available at the Clarksville Research Center. Phenotypic data for these traits will be collected for two years (starting in 2019). Test individuals will be genotyped using the RosBREED Infinium Ilumina array v.2 (Peace et al., 2012; Vanderzande et al., 2019) and QTL analyses will be performed as in Cai et al. (2017). If functional alleles are identified for any of the QTL that explain over at least 10% of the phenotypic variation for the trait in at least one population, DNA markers will be designed and used to conduct marker-assisted selection. To aid in the determination of the causal genes underlying the QTL, RNA expression profiles using RNA-Seq will be obtained from a fruit development time course series for a minimum of six individuals that exhibit different phenotypes and functional alleles for these traits. The resulting reads will be mapped to the three sweet cherry reference maps, one of which is published (Shirasawa et al., 2017) and two of which are in progress (E. Dirlewanger, pers. comm., M. Morgante, pers. comm.). Transcript abundances will be estimated and used to suggest candidate genes and causal variants that underlie the targeted QTLs.Dissecting the chromosome 4 bloom and maturity time QTL cluster: Offspring from populations segregating for late bloom time will be genotyped as described above and phenotyped for both bloom and maturity time to identify individuals that bloom late but ripen mid- or late-season. Those rare offspring may have a recombination at this QTL cluster. The QTL cluster will be sequenced from these offspring and their parents to fully describe the cis-configuration of the involved haplotypes. This will allow the precise location of any recombinations and aid in refining the location of the bloom and maturity time QTLs. The expected outcomes will be knowledge of alleles for loci that contribute to late flowering and early ripening, and the characterization of individuals with rare favorable allele combinations that become can be used as parents in the breeding program and also be tested for their potential as new cultivars.

Progress 07/01/19 to 09/30/21

Outputs
Target Audience:Target audiences included Prunus breeders and allied scientists, cherry growers, processors and marketing organizations, the tree fruit nursery industry, and consumers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One graduate student contributed to this work. How have the results been disseminated to communities of interest?Communities of interest received project results via presentations at industry meetings in December and January, a field day in August and through numerous one-on-one grower and processor interactions. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Sour cherry breeding: Sour cherry seedlings planted in the field were evaluated for numerous horticultural traits including bloom time, maturity time, fresh and frozen fruit quality characteristics, and reaction to cherry leaf spot. Cherry leaf spot tolerance exhibited in some sour cherry germplasm is hypothesized to be controlled by genetic factors from sweet cherry, as sweet cherry is one of the progenitor species of sour cherry. Due to pressure from the new invasive insect, Spotted Winged Drosophila (SWD), there is interest in identifying individuals that bloom late and ripen early. Harvesting sour cherry at an earlier time in the season has the potential to increase grower profitability due to fewer sprays required to control this insect threat, along with less insect pressure. Unfortunately, late bloom time is associated with late ripening time; however, offspring that had the desired bloom and maturity times and good fruit quality were identified. This year, two additional selections that exhibit tolerance to cherry leaf spot and have excellent eating quality and phenology traits, were budded to provide trees for advanced testing. Breeding Armillaria tolerant cherry rootstocks: Loss of sweet and sour cherry trees to Armillaria root rot is a severe threat to the future of the cherry industries in Michigan as there are no cultural practices or resistant rootstocks that can mitigate the tree loss and many fruit sites could be lost to cherry production. Therefore breeding Armillaria tolerant cherry rootstocks is a high priority. In Prunus, Armillaria tolerance has been identified in P. cerasifera, and this tolerance is likely due to its ability to wall off fungal invasion. Unfortunately, P. cerasifera is not graft compatible with cherry. Therefore, in 2021, crosses were made between P. cerasifera and three cherry species with the goal of combining tolerance to Armillaria with graft compatibility. Putative hybrid seeds are being germinated by collaborators at Clemson Univ. and confirmed hybrids will enter a phenotyping pipeline. Dwarfing precocious rootstocks: Five MSU cherry rootstocks that increase scion precocity and induce scion dwarfing have been patented and licensed to commercial nurseries. All five rootstocks are candidates for use in high density sweet cherry plantings. Two more MSU cherry rootstocks that result in semi-dwarf trees have been identified and patents have been applied for. These rootstocks may be suitable for sour cherry and medium vigor sweet cherry planting systems. Cherry genetics: Sour cherry is an allotetraploid species resulting from an interspecific cross between sweet cherry (P. avium) and ground cherry (P. fruticosa). One of the biggest challenges of sour cherry breeding is low fruit set, which may be due to irregular chromosome pairing and separation at meiosis causing a loss in fertility. These meiotic irregularities could be caused by unbalanced subgenome dosages resulting from progenitor introgressions and/or biased fractionation of subgenomes following hybridization. Our goal was to investigate the subgenome origin of the sour cherry cultivar 'Montmorency' to determine if it exhibits balanced subgenome dosage. This project was enabled by the availability of the new 'Montmorency' reference genome, a new draft genome of P. fruticosa, and the Tieton v2.0 reference genome for P. avium. Using these sequences, a list of gene orthologs was identified across the three genomes and rates of synonymous mutation (Ks) were used to assign progenitor species origin to 63.8 percent of the genes on the 'Montmorency' genome. Results indicated that 'Montmorency' exhibited an overall higher content of P. avium-derived genes, suggesting that sour cherry has had more introgressions with P. avium than P. fruticosa in the wild, has experienced biased fractionation resulting in preferential retention of the P. avium subgenome, or some combination of the two events.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Iezzoni AF, McFerson J, Luby J, Gasic K, Whitaker V, Bassil N, Yue C, Gallardo K, McCracken V, Coe M, Hardner C, Zurn JD, Hokanson S, van de Weg E, Jung S, Main D, da Silva Linge C, Vanderzande S, Davis TM, Mahoney LL, Finn C, Peace C. (2020) RosBREED: bridging the chasm between discovery and application to enable DNA-informed breeding in rosaceous crop. Horticulture Research 7:177 doi.org/10.1038/s41438-020-00398-7
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Ljubojevic M, Sebolt A, Ognjanov V, Iezzoni A. (2021) Heritability of anatomical characteristics in cherry interspecific hybrids. Journal of Plant Growth Regulation https://doi.org/10.1007/s00344-021-10357-8
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Vanderzande S, Zheng P, Cai L, Barac G, Gasic K, Main D, Iezzoni A, Peace C (2020)The cherry 6+9K SNP array: a cost-effective improvement to the cherry 6K SNP array for genetic studies. Scientific Reports 10:7613. doi.org/10.1038/s41598-020-64438-x
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Devkota P, Iezzoni A. Gasic K, Reighard G, Hammerschmidt R (2020) Evaluation of the susceptibility of Prunus rootstock genotypes to Armillaria and Desarmillaria species. Eur J Plant Pathology 158:177193 doi.org/10.1007/s10658-020-02065-y

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

Outputs
Target Audience:Target audiences included Prunus breeders and allied scientists, cherry growers, processors and marketing organizations, the tree fruit nursery industry, and consumers. Changes/Problems:Covid 19 restrictions on research hampered out ability to repeat a RNA flower and fruit growth and development time course of field grown materials. This work is planned for 2021. What opportunities for training and professional development has the project provided?One graduate student contributed to this work. How have the results been disseminated to communities of interest?Communities of interest received project results via presentations at industry meetings in December and February and through a video postings for a "virtual field day". What do you plan to do during the next reporting period to accomplish the goals?Sour cherry breeding: Hybridizations will be made in the spring between individuals projected to be superior parents. This will include seedlings previously identified that are late blooming and early ripening. The resulting seedlings will be grown in a greenhouse at the MSU campus. Seedlings from families predicted to be segregating for self-in/compatibility, dark flesh color, and P. canescens-derived cherry leaf spot resistance will be screened using DNA markers to identify undesirable individuals. Those individuals predicted to have the undesirable traits will be discarded prior to field planting at MSU's Clarksville Research Center. Seedlings predicted to be especially useful due to their combination of alleles will be budded on precocious rootstocks to accelerate flowering and fruiting. Seedlings planted in the field in prior years will be evaluated for numerous horticultural traits including bloom date, harvest date, fruiting habit, and fresh and frozen fruit quality characteristics. Superior selections will be propagated and planted at test sites in Michigan to provide additional locations to observe these selections plus sufficient trees for yield data, mechanical harvesting and fruit for pilot processing trials. Cherry rootstock breeding: Armillaria resistance: To breed new Armillaria resistant rootstocks, crosses will again be attempted between cherry and plum clones suspected to exhibit tolerance to Armillaria. The yield of viable seeds from these interspecific crosses is very low; hence, continued efforts to generate as many interspecific hybrids as possible is necessary. Dwarfing precocious rootstocks: The suitability of the MSU candidate cherry rootstocks to enable an over-the-row production system for sour cherry and a pedestrian orchard for sweet cherry will be evaluated in existing trials in Michigan. Yield and trunk cross-sectional area will be recorded from trees in these trials along with fruit quality traits. Cherry genetics: Investigations will focus on a genomic region on linkage group 4 where major loci controlling bloom time, maturity time and fruit firmness co-locate. RNA will be sampled from a time course over the fruit and development period to provide gene expression data. DNA sequence will be queried to identify genomic variants associated with the different functional haplotypes for these loci. In addition, the presence of subgenome dominance for this region in tetraploid sour cherry will be investigated. The ultimate goals are to identify genetic factors that control trait variation and to develop DNA markers that can be used for marker-assisted breeding.

Impacts
What was accomplished under these goals? Sour cherry breeding: Sour cherry seedlings planted in the field were evaluated for numerous horticultural traits including bloom time, maturity time, fresh and frozen fruit quality characteristics, and reaction to cherry leaf spot. Donor sources used for cherry leaf spot were the wild species Prunus canescens (resistance) and sweet cherry (tolerance). Due to pressure from the new invasive insect, Spotted Winged Drosophila (SWD), there is interest in identifying individuals that bloom late and ripen early. Harvesting sour cherry at an earlier time in the season has the potential to increase grower profitability due to fewer sprays required to control this insect threat, along with less insect pressure. Unfortunately, late bloom time is associated with late ripening time; however, offspring that had the desired bloom and maturity times and good fruit quality were identified and advanced along with five other individuals that had excellent fruit quality targeting the fresh market. Rootstock breeding: Armillaria resistance: Six Michigan field trials were planted in 2016 to determine if the putatively Armillaria resistant species P. maackii has commercial potential as a rootstock for cherry production. To date, several trees of P. maackii and the susceptible control, P. mahaleb, have died and Armillaria has been isolated from the dead roots. Although P. maackii roots have been shown to produce unique antifungal compounds, it appears as if this defense mechanism is insufficient under high pathogen pressure. In 2020, Montmorency trees on P. mahaheb rootstock tended to have higher yields than trees on P. maackii rootstocks, despite the P. maackii trees being larger. Taken together, these results suggest that P. maackii may not be a suitable alternative cherry rootstock. P. cerasifera exhibited tolerance to Armillaria following in vitro inoculation, which is likely due to its ability to wall off fungal invasion. Unfortunately, P. cerasifera is not graft compatible with cherry. Therefore, in 2019 and again in 2020, crosses were made between P. cerasifera and three cherry species with the goal of combining tolerance to Armillaria with graft compatibility. Putative hybrids have been germinated in vitro by collaborators at Clemson Univ. and will enter a phenotyping pipeline. Dwarfing precocious rootstocks: Five MSU cherry rootstocks that increase scion precocity and dwarfing have entered the second testing phase.For sour cherry, yield data was obtained from existing rootstocks trials at the Michigan State University Northwest Horticultural Research Center. The findings indicated that the MSU rootstocks are suitable for an over-the-row harvest planting system compared to the sour cherry commercial standard non-dwarfing rootstock, P. mahaleb, but productivity and tree stress tolerance varied among the five rootstocks. An additional eight trials planted in 2017, compare the MSU rootstocks and other size controlling rootstocks with both sweet and sour cherry scions in Washington, Oregon and Michigan. The MSU rootstocks are also included in NC140 trials in Washington, Michigan, Wisconsin, New York, and Utah. Cherry genetics: Genome sequence data is being analyzed from an array of cherry individuals representing the different linkage group 4 haplotypes to enable the identification of genomic variants associated with the major bloom time, maturity time and fruit firmness loci that map to this region. In 2020, this analysis was broadened to include a comparison of the peach linkage group 4 region.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Calle, A., Cai, L., Iezzoni, A., W�nsch, A. 2020. Genetic dissection of bloom time in low chilling sweet cherry (Prunus avium L.) using a multi-family QTL approach. Front. Plant Sci. 10: article 1647, doi.org/10.3389/fpls.2019.01647.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Pinosio, S., Marroni, F., Zuccolo, A., Vitulo, N., Mariette, S., Sonnante, G., Aravanopoulos, F.A., Ganopoulos, I., Palasciano, M., Vidotto, M., Magris, G., Iezzoni, A., Vendramin, G.G., Morgante, M. 2020. A draft genome of sweet cherry (Prunus avium L.) reveals genome-wide and local effects of domestication. The Plant Jour. 103:1420-1432.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Calle, A., Balas, F., Cai, L., Iezzoni, A., Lopez-Corrales, M., Serradilla, M.J., Wunsch, A. 2020. Fruit size and firmness QTL alleles of breeding interest identified in a sweet cherry Ambrun�s � Sweetheart population. Mol. Breeding 40, 86. https://doi.org/10.1007/s11032-020-01165-1
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Zurn, J.D., Driskill, M., Jung, S., Main, D., Yin, M.H., Clark, M.C., Cheng, L., Ashrafi, H., Aryal, R., Clark, J.R., Worthington, M., Finn, C.E., Peace, C., Iezzoni, A., Bassil, N. 2020. A Rosaceae family-level approach to identify loci influencing soluble solids content in blackberry for DNA-informed breeding. G3 (Bethesda) doi: 10.1534/g3.120.401449
• Type: Conference Papers and Presentations Status: Other Year Published: 2020 Citation: Gasic, K., Cai, L., Rhoades, K. E. B., Da Silva Linge, C., Li, Z., Saski, C., McCord, P. Iezzoni, A. F. (Aug. 2020) Haplotype Diversity of a QTL Hotspot on Chromosome 4 in Peach and Sweet Cherry. Talk presented at the meeting of the American Society of Horticulture Science, virtual meeting.

Progress 07/01/19 to 09/30/19

Outputs
Target Audience:Target audiences included Prunus breeders and allied scientists, cherry growers, processors and marketing organizations, the tree fruit nursery industry, and consumers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A technician, one graduate students and two undergraduate students contributed to this work. How have the results been disseminated to communities of interest?Communities of interest received project results via presentations at industry meetings and field days. What do you plan to do during the next reporting period to accomplish the goals?Sour cherry breeding: Hybridizations will be made in the spring between individuals projected to be superior parents. This will include seedlings previously identified that are late blooming and early ripening. The resulting seedlings will be grown in a greenhouse at the MSU campus. Seedlings from families predicted to be segregating for self-in/compatibility, dark flesh color, and P. canescens-derived cherry leaf spot resistance will be screened using DNA markers to identify undesirable individuals. Those individuals predicted to have the undesirable traits will be discarded prior to field planting at MSU's Clarksville Research Center. Seedlings predicted to be especially useful due to their combination of alleles will be budded on precocious rootstocks to accelerate flowering and fruiting. Seedlings planted in the field in prior years will be evaluated for numerous horticultural traits including bloom date, harvest date, fruiting habit, and fresh and frozen fruit quality characteristics. Superior selections will be propagated and planted at test sites in Michigan to provide additional locations to observe these selections plus sufficient trees for yield data, mechanical harvesting and fruit for pilot processing trials. Cherry rootstock breeding: Armillaria resistance: Field trials were planted in 2016 to test the potential resistance of P. maackii to Armillaria. Growth, tree health, tree survival and horticultural performance will continue to be monitored for the 'Montmorency' P. maackii and P. mahaleb trees planted at the Armillaria sites and for the P. maackii trees with 'Montmorency' scion. Any dead trees will be evaluated to determine the cause of death. To breed new Armillaria resistant rootstocks, crosses will be attempted between cherry and plum clones suspected to exhibit tolerance to Armillaria. Dwarfing precocious rootstocks: The suitability of the MSU candidate cherry rootstocks to enable an over-the-row production system for sour cherry and a pedestrian orchard for sweet cherry will be evaluated in existing trials in Michigan, Washington, and Oregon. Yield and trunk cross-sectional area will be recorded from trees in these trials along with fruit quality traits. Cherry genetics: Investigations will focus on a genomic region on linkage group 4 where major loci controlling bloom time, maturity time and fruit firmness co-locate. DNA sequence data obtained in 2019 will be queried to identify genomic variants associated with the different functional haplotypes for these loci. The ultimate goals are to identify the genomic bases of the functional alleles and develop DNA markers that can be used for marker-assisted breeding.

Impacts
What was accomplished under these goals? Sour cherry breeding: Sour cherry seedlings planted in the field were evaluated for numerous horticultural traits including bloom time, maturity time, fresh and frozen fruit quality characteristics, and reaction to cherry leaf spot. Donor sources used for cherry leaf spot were the wild species Prunus canescens (resistance) and sweet cherry (tolerance). Due to pressure from the new invasive insect, Spotted Winged Drosophila (SWD), there is interest in identifying individuals that bloom late and ripen early. Harvesting sour cherry at an earlier time in the season has the potential to increase grower profitability due to fewer sprays required to control this insect threat, along with less insect pressure. Unfortunately, late bloom time is associated with late ripening time; however, three offspring that had the desired bloom and maturity times and good fruit quality were identified for advancement. Breeding efficiency was increased by the use of DNA tests for fruit flesh color and Prunus canescens-derived cherry leaf spot resistance. Seedlings from crosses that were predicted to segregate for these traits were screened using DNA tests and only those seedlings with the desirable fruit color and disease resistance alleles were planted in the breeding orchard. Rootstock breeding: Armillaria resistance: Six Michigan field trials were planted in 2016 to determine if the putatively Armillaria resistant species P. maackii has commercial potential as a rootstock for cherry production. To date, several trees of P. maackii and the susceptible control, P. mahaleb, have died and Armillaria has been isolated from the dead roots. Although P. maackii roots have been shown to produce unique antifungal compounds, it is possible that this defense mechanism is insufficient under high pathogen pressure. Armillaria inoculation experiments of P. cerasifera suggest that this plum species may be a good source of tolerance due to its ability to wall off fungal invasion. Unfortunately, P. cerasifera is not graft compatible with cherry. Therefore, in 2019, crosses were made between P. cerasifera and three cherry species with the goal of combining tolerance to Armillaria with graft compatibility. Dwarfing precocious rootstocks: Five MSU cherry rootstocks that increase scion precocity and dwarfing have entered the second testing phase. For sweet cherry, three trials comparing the MSU cherry rootstocks with other size controlling rootstocks were planted in grower orchards in spring 2015 in Oregon (one site) and Washington (two sites). The trees were planted and trained according to high density orchard systems to determine the rootstocks and training systems most likely to result in profitable production. Yield data indicated that these rootstocks grown in high density production systems would result in an increase in fruit production in years 2 and 3 compared to production in 3 to 5 for standard orchard systems. For sour cherry, yield data was obtained from existing rootstocks trials at the Michigan State University Northwest Horticultural Research Center. The findings indicated that the MSU rootstocks are suitable for an over-the-row harvest planting system compared to the sour cherry commercial standard non-dwarfing rootstock, P. mahaleb, but productivity and tree stress tolerance varied among the five rootstocks. An additional eight trials planted in 2017, compare the MSU rootstocks and other size controlling rootstocks with both sweet and sour cherry scions in Washington, Oregon and Michigan. The MSU rootstocks are also included in NC140 trials in Washington, Michigan, Wisconsin, New York, and Utah. Cherry genetics: Phenotypic data was recorded for sour cherry progeny populations segregating for high priority traits to include bloom date, maturity date and fruit firmness. Major loci controlling these three traits have been show to cluster on cherry linkage group 4 and haplotypes associated with the phenotypic variation for these major loci were determined. Genome sequence data was obtained from an array of cherry individuals representing the different linkage group 4 haplotypes to enable the identification of genomic variants associated with trait variation for these major bloom time, maturity time and fruit firmness loci.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Goeckeritz C, Azmi A, Iezzoni A, Hollender C. 2019. Untangling the mechanism of bloom time differences in a population of tart cherry (Prunus cerasus). FASEB  The Mechanisms in Plant Development Conference, Olean, NY.