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Amy F. Iezzoni

The sour cherry (Prunus cerasus L.) industry in the United States is a monoculture of a 400-year-old cultivar from France named `Montmorency'. To provide a solid germplasm base to breed alternatives to `Montmorency', cherry germplasm was systematically collected over a 15-year period from its ancestral home in Central and Eastern Europe and introduced to the U.S. The strategy of germplasm collection using pollen, seed and budwood importation of highly quarantined species is discussed. Germplasm resulting from this effort is highlighted as well as an example of commercial success. Finally, the “recycling” of this immense germplasm collection to search for dwarfing precocious rootstocks for sweet cherry is described.

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Amy F. Iezzoni and Marvin P. Pritts

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Amy F. Iezzoni and Colleen A. Mulinix

Bloom times were evaluated for seedlings from four full-sib and 14 open-pollinated families of sour cherry (Prunus cerasus L.). Time of anthesis for individual seedlings ranged over 17and 16-day periods in 1989 and 1990, respectively. In both years, most seedlings bloomed later than `Montmorency', the only commercially important sour cherry cultivar in the United States. `Pitic de Iasi', the parent of the latest-blooming family, is a natural interspecific hybrid between sour cherry and the cold-hardy Russian ground cherry (P. fruticosa Pall.). Hybridization between sour and ground cherry and intense selection pressure in the colder areas of the sour cherry habitat may have favored selection of the late-blooming character.

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Thomas S. Brettin and Amy F. Iezzoni

Sour cherry (Prunus cerasus) is an allotetraploid with sweet cherry (P. avium) and ground cherry (P. fruticosa) as the proposed progenitor species. Three cpDNA markers from eight sweet, four ground, and 26 sour cherry selections were analyzed to investigate the relatedness of their cp genomes. To date, two RFLP polymorphisms have been identified with both the P2 and P4 fragments of tomato cpDNA, while four length polymorphisms of an intergenic spacer have been identified by PCR amplification. Sweet and ground cherry have different cp polymorphisms, while sour cherry individuals have been identified that have the sweet and ground cherry polymorphisms plus a unique polymorphism. Additional individuals chosen to represent the diversity within each species will be screened to provide a more complete assessment of cp diversity. In addition, progeny from a sour cherry cross where the parents have different cp polymorphisms are being evaluated to determine if the chloroplasts are exclusively maternally inherited.

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Suzanne L. Downey and Amy F. Iezzoni

Black cherry (Prunus serotina Ehrh.) is a common secondary forest species with a wide endemic distribution ranging from Nova Scotia south into Mexico, Ecuador, and Peru. Although planted in the United States for its valued lumber, black cherry is essentially a wild species with small fruit ≈6 to 10 mm in diameter. In contrast, in Mexico and Ecuador, domesticates of this species called Capulin, have much larger (2 to 2.5 cm in diameter) edible fruit. To date, no studies of the genetic diversity within North American black cherry or the ancestral origin of the Capulin types have been conducted. Simple sequence repeats (SSRs, also termed microsatellites) would be the marker of choice for such genetic diversity studies due to their hypervariability; however, generation of these sequence-based markers is expensive. Therefore, our objective was to determine if markers already identified in other Prunus L. species would be informative in black cherry. The black cherry germplasm screened consisted of selections originating from Michigan, Mexico, and Ecuador. A chloroplast DNA marker, originally generated from sour cherry (P. cerasus L.), amplified three different sized products in black cherry. Four of the eight nuclear SSR markers tested from peach [P. persica L. Batsch (Peach Group)], sour cherry, and sweet cherry (P. avium L.) also amplified and identified polymorphic markers. Together these four primer pairs resolved 54 putative alleles for the 66 black cherry accessions assayed. Success of the sweet cherry, peach, and sour cherry primers in identification of polymorphic markers in black cherry indicates it should be possible to use these markers for comprehensive molecular genetic studies in black cherry.

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Amy F. Iezzoni and Colleen A. Mulinix

Yield components were measured from 115 sour cherry (Prunus cerasus L.) hybrid seedlings from 13 full-sib families to investigate the potential of breeding for increased yield. Those families with the highest number of fruit and reproductive buds had the highest yields. In general, increased fruit size was not able to compensate for low fruit count. Fruit set and flower count per bud were inversely related, suggesting compensation between these two components. Yield components from six selections chosen for differing fruiting habits were measured for an additional 2 years. In year 1, those selections with a majority of their fruit on l-year-old wood had higher yield efficiencies (yield per branch cross-sectional area) than those with fruit on spurs; however, but year 3, the higher-yielding selections were those that fruited primarily on spurs. The data are discussed relative to selecting for yield in a sour cherry breeding program.

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James W. Olmstead, Amy F. Iezzoni and Matthew D. Whiting

Understanding the genetic control of fruit size in sweet cherry (Prunus avium L.) is critical for maximizing fruit size and profitable fresh market production. In cherry, coordinated cycles of cell division and expansion of the carpel result in a fleshy mesocarp that adheres to a stony endocarp. How these structural changes are influenced by differing genetics and environments to result in differing fruit sizes is not known. Thus, the authors measured mesocarp cell length and cell number as components of fruit size. To determine the relative genotypic contribution, five sweet cherry cultivars ranging from ≈1 to 13 g fresh weight were evaluated. To determine the relative environmental contribution to fruit size, different-size fruit within the same genotype and from the same genotype grown in different environments were evaluated. Mesocarp cell number was the major contributor to the differences in fruit equatorial diameter among the five sweet cherry cultivars. The cultivars fell into three significantly different cell number classes: ≈28 cells, ≈45 cells, and ≈78 cells per radial mesocarp section. Furthermore, mesocarp cell number was remarkably stable and virtually unaffected by the environment as neither growing location nor physiological factors that reduced final fruit size significantly altered the cell numbers. Cell length was also significantly different among the cultivars, but failed to contribute to the overall difference in fruit size. Cell length was significantly influenced by the environment, indicating that cultural practices that maximize mesocarp cell size should be used to achieve a cultivar's fruit size potential.

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Christopher M. Long, Colleen A. Mulinix and Amy F. Iezzoni

Microspore-derived callus cultures were obtained by anther culture of `Emperor Francis' sweet cherry (Prunus avium L.). Branches were removed from the field in January and March and forced in the laboratory. When the microspores reached the uninucleate stage, anthers were placed on modified Quoirin and Lepoivre liquid culture medium containing 4.4 μm BA and 4.5 μm 2,4-D. After ≈60 days, callus that emerged from the anthers was placed on woody plant medium supplemented with 1 μm 2,4-D and 3 μm 2iP and routinely transferred. The resulting 270 callus cultures were screened for two allozymes heterozygous in `Emperor Francis', Pgi-2 and 6-Pgd-1. Of the 270 callus cultures, 154 expressed only one allele each for Pgi-2 and 6-Pgd-1; thus, they were considered microspore-derived. The microspore-derived callus cultures can be used as a linkage mapping population. Chemical names used: 6-benzyladenine (BA); 2,4-dichlorophenoxyacetic acid (2,4-D); N6-(2-isopentenyl)-adenine (2iP).

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James W. Olmstead, Amy F. Iezzoni and Matthew D. Whiting

Although maximizing fruit size is critical for profitable sweet cherry (Prunusavium L.) production, little is known about the cellular differences among and between cultivars that contribute to fruit size differences. A wide range of fruit size exists among sweet cherries, and, due to cultural and environmental differences, significant variation exists among genetically identical fruit from the same cultivar. To determine the relative contributions of flesh cell number and cell size to final fruit size in sweet cherry, equatorial sections of three cultivars with a wide range in final average fruit size [`New York 54' (NY54; 1.4 g fresh weight, 11.8 mm diameter), `Emperor Francis' (EF; 6.1 g, 21.0 mm), and `Selah' (12.8 g, 25.5 mm)] were created from mature fruit. Cells intersecting a transverse line were counted and average cell length was calculated. The average cell numbers were significantly different (P ≤ 0.05) between `NY54', `EF', and `Selah' (26.7, 47.4, and 83.2, respectively), indicating that flesh cell number is the major contributor to differences in fruit size between cultivars. Flesh cell numbers of `NY54', `EF', and `Selah' were similar at bloom and increased rapidly for a short duration after fertilization, suggesting a key developmental period for fruit size differences. To determine the contribution of cell number differences to variation in fruit size within a cultivar, fruit from `Bing' and `Regina' trees exhibiting a range of size due to cultural and environmental differences were measured. In both cases, average cell number was not significantly different (P = 0.9, P = 0.3, respectively), while average cell size was (P ≤ 0.05), further indicating fruit flesh cell number is a genetically controlled trait.

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Nathanael R. Hauck, Amy F. Iezzoni, Hisayo Yamane and Ryutaro Tao

Correct assignment of self-incompatibility alleles (S-alleles) in sweet cherry (Prunus avium L.) is important to assure fruit set in field plantings and breeding crosses. Until recently, only six S-alleles had been assigned. With the determination that the stylar product of the S-locus is a ribonuclease (RNase) and subsequent cloning of the S-RNases, it has been possible to use isoenzyme and DNA analysis to genotype S-alleles. As a result, numerous additional S-alleles have been identified; however, since different groups used different strategies for genotype analysis and different cultivars, the nomenclature contained inconsistencies and redundancies. In this study restriction fragment-length polymorphism (RFLP) profiles are presented using HindIII, EcoRI, DraI, or XbaI restriction digests of the S-alleles present in 22 sweet cherry cultivars which were chosen based upon their unique S-allele designations and/or their importance to the United States sweet cherry breeding community. Twelve previously published alleles (S1, S2, S3, S4, S5, S6, S7, S9, S10, S11, S12, and S13) could be differentiated by their RFLP profiles for each of the four restriction enzymes. Two new putative S-alleles, both found in `NY1625', are reported, bringing the total to 14 differentiable alleles. We propose the adoption of a standard nomenclature in which the sweet cherry cultivars `Hedelfingen' and `Burlat' are S3S5 and S3S9, respectively. Fragment sizes for each S-allele/restriction enzyme combination are presented for reference in future S-allele discovery projects.