Stone Fruit Breeding Research Articles

Genetic resources of the genus Prunus L. and their role in stone fruit breeding

Stone fruits such as apricot, cherry plum, cherry, peach, plum, and sweet cherry are highly popular in the Russian Federation. They are cultivated in the industrial gardens of large agricultural producers, as well as the plantings on farms and household plots. The fruits of these species can be consumed fresh for a considerable period of time. The application of some processing methods (cooling, freezing, and storage in a special atmosphere) significantly extends this period. Stone fruits are also suitable for producing a wide variety of processed products. The biochemical composition of fruits determines their high energy value and dietary properties. The representatives of the genus Prunus L. exhibit great genetic diversity. Due to their high polymorphy, they cover a large area. In regions with favorable weather and climatic growth conditions, stone fruits constitute the main industrial varieties. High requirements for industrial varieties determine the relevance of breeding improvement of available varieties. Representatives of the genus Prunus are characterized by a long juvenile period, different ploidy of species, high incompatibility, as well as heterozygosity for a large number of traits with a comparatively small number of identified genes. This fact significantly complicates genetic studies. The assortment of stone fruit crops in central Russia was renewed in several main directions. Most varieties were created through intervarietal crosses within a species. The current breeding work is aimed at creating new stone fruit species, as well as at improving the existing assortment. Along with the crossing of geographically distant varieties within a species, distant hybridization is one of the promising directions. In this way, new cultivated species were created, e.g., Russian plum (P. rossica Erem.), which is widely used in plantings. Such varieties are characterized by an attractive appearance, large size, pleasant aroma, and great flavor of fruits, as well as resistance to frost and rotting.

Embryo rescue in stone fruit breeding: specifics and application success

The development of stone fruit varieties that meet modern production requirements is a labor-intensive process involving low yields of progeny obtained through controlled intraspecific and interspecific hybridization, which can take up to 25 years. The non-viability of hybrid seeds is caused by the abortion of the embryo that does not have time to complete its morphophysiological development and endosperm abortion in interspecific hybrids. It is possible to preserve hybrids having a unique combination of traits by removing embryos derived from interspecific and intergeneric crossing that are unable to survive in vivo or when using conventional methods for breeding embryos at early developmental stages and placing them under in vitro conditions for further development. On the basis of literary sources, the study aims to analyze growth media, conditions of their application, and time of embryo placement under in vitro conditions designed to preserve immature embryos and create hybrids of stone fruit crops, as well as to identify the most effective in vitro embryo isolation schemes for further use in the breeding process. The analytical review used open sources containing information on the composition of the most commonly used growth media, their compositions, modifications, application conditions, time of embryo placement under in vitro conditions for common peach (Prunus persica (L.) Batsch.), common apricot (P. armeniaca L.), common plum (P. domestica L.), Chinese plum (P. salicina Lindl.), cherry plum (P. cerasifera Ehrh.), sloe (P. spinosa L.), sour cherry (P. cerasus L.), sweet cherry (P. avium (L.) L.), as well as electronic scientific libraries (eLibrary, Scopus, and Google Scholar). The performed analysis of works revealed the following media as optimal for sustaining the development of embryos: common peach – modified growth medium Woody Plant (up to 100 % of preserved embryos); common apricot – modified Monnier (up to 92.4 % of preserved embryos); sour cherry, sweet cherry, plum, and interspecific hybrids – different variants of Murashige and Skoog (over 70 % of preserved embryos). The used modifiers include 6-benzylaminopurine (6-BAP), gibberellic acid (GA), kinetin, peracetic acid, carbohydrates, L-glutamine, iron chelate, ascorbic acid, thiamine, glutamic acid, tryptophan, casein hydrolysate, etc. The time of placement under in vitro conditions varies from 28 days (sour cherry) to 99 days (common peach) depending on the crop. Stratification in the dark at +4…+5 ℃ prior to development increases the yield of viable embryos. The optimal photoperiod for in vitro embryo cultivation ranges from 12 (common peach) to 16 (cherry plum, sour cherry, sweet cherry, and interspecific hybrids) hours. As a result of selection from the fund of hybrids obtained through embryo preservation, one common peach variety (Krymskii Shedevr) and three sweet cherry varieties (Vesnyany Naspivy, Prizerka, and Uslada), recommended for the North Caucasus region, were included in the State Register of Breeding Achievements approved for use; two common plum varieties (Tulitsa and Velichavaya) were included into the Register of Protected Breeding Achievements for the Central Region.

Survey of Xylella fastidiosa Infection in Prunus Germplasm in Gainesville, FL, USA

The pathogen Xylella fastidiosa is a xylem-restricted, gram-negative bacterium that is known to cause diseases of many cultivated plant species. Recent outbreaks of X. fastidiosa diseases in Europe have brought attention to the impact of this pathogen, especially to perennial crops. Among the Prunus genus, X. fastidiosa is known to have a wide range of hosts, including plum, almond, peach, cherry, and apricot. Infected trees have reduced fruit quality, possibly resulting in unmarketable fruits, as well as reduced lifespan. There are no curative management options for X. fastidiosa diseases in Prunus; therefore, development of resistant or tolerant cultivars through breeding represents an efficient option to reduce the impact of this pathogen. In this context, the main objective of this study was to determine the occurrence of X. fastidiosa in germplasm of the Stone Fruit Breeding Program at the University of Florida located in Gainesville, FL, USA, under natural infection conditions. A total of 43 individuals representing 10 different genotypic groups within the Prunus genus were tested for the presence of X. fastidiosa. Additionally, we report a novel and easy sampling method using sawdust collected from tree trunks for the detection of this pathogen in Prunus and the development of an endogenous control for improving the diagnosis of this pathogen using real-time polymerase chain reactions. Our results showed a high incidence of X. fastidiosa in the germplasm tested, with more than 65% of the samples positive for the presence of the bacterial pathogen. However, X. fastidiosa was not detected in most of the P. mume samples tested, whereas almost all the P. mume × P. armeniaca hybrids were positive. Negative individuals were also identified in P. avium, P. campanulata, P. umbellata, and P. salicina × P. ceracifera. These trees have been planted in the field, exposed to natural infection for 4 to 11 years, and are considered to show field resistance. Finally, primers and probes based on the Prunus COX gene developed in this study can be used as an internal amplification control to enhance the interpretation of results of X. fastidiosa detection assays using sawdust samples.

Growth, yield, and biochemical behaviors of important stone fruits affected by plant genotype and environmental conditions

Stone fruit breeders face a significant challenge in obtaining new and high-yielding cultivars, and utilizing unknown ones. Among stone fruit, peaches and nectarines are the most prominent fruits. To address this issue, three independent experiments were conducted on various peach and nectarine cultivars and genotypes at two locations in Iran during 2018–2019 and 2019–2020 using a randomized complete block design with three replications. The results showed significant variations in growth, yield, and biochemical behaviors among the different genotypes and cultivars. 'Henri' was found to have superior yield, tissue firmness, and total soluble solids. Additionally, certain peach cultivars, such as 'Fayette', 'Sorkho-Sefid-Mashhad', and 'Shandabad', had higher yield efficiency than the control cultivar 'J.H. Hale'. Furthermore, 'PMsh-5′ had higher levels of ascorbic acid, antioxidant capacity, and carotenoids. 'Haj-Kazemi' had the tallest average tree height, trunk diameter, and crown of the tree in Golmakan, while 'Anjiri-Zaferani' had the highest levels of total soluble solids, flavor index, and pH. Based on these findings, 'Flamino', 'Nectared', and 'Henri' are recommended as the best nectarine cultivars in Mashhad due to their high pomological and phenological traits. 'Shasta', 'Sorkho-Sefid Mashhad', and 'Suncrest', as well as 'Fayette' and 'Shandabad-Hasteh-Joda' peaches, are recommended as superior cultivars for Mashhad and Golmakan, respectively. This study highlights the importance of selecting appropriate cultivars for optimal growth and yield and emphasizes the need for further research in stone fruit breeding.

Assessment of Prunus Rootstock Accessions Using Chloroplast and Nuclear Microsatellites

Abstract A rootstock collection of Prunus species and hybrids is maintained at the U.S. Department of Agriculture stone fruit breeding program at Byron, GA. We genotyped 66 Prunus rootstock accessions and clones using chloroplast and nuclear microsatellites in this study. Chloroplast microsatellites revealed that the accessions belong to four previously defined maternal lineage groups (MLG-1 to -4) and five new ones (MLG-9 to -13). MLG-1 and -2 share the same chloroplast alleles of ‘Chinese Cling’ peach (Prunus persica) derived scions and American scions and rootstocks related to early European introductions, respectively. MLG-3 included ‘Guardian’ rootstock and its descendants. MLG-4 had a single genotype, ‘Okinawa’, that is the maternal parent of ‘Flordaking’. MLG-9 and MLG-11 to -13 included hybrids with different plums (Prunus salicina, Prunus cerasifera, Prunus tomentosa, or Prunus angustifolia) in their maternal parentage. MLG-10 included hybrids from almond (Prunus. dulcis) in the maternal parentage. The neighbor-joining phylogenetic tree based on nuclear microsatellite genotyping data showed several clusters. Cluster I included only one scion cultivar Elberta from MLG-1. Clusters II, III, and V contained peach accessions mostly in MLG-2. Clusters IV and VI included accessions mostly in MLG-3. Cluster VII included most accessions of plum-peach hybrid origin and those found within MLG-13. Cluster VIII was found to be mixed with different plum-peach hybrids and hybrids from other Prunus species, most of which were found in MLG-10, -11, and -12. Most accessions in Cluster IX were related to plums in MLG-11 and a few accessions in MLG-9.

‘Crimson Joy’ Peach

The U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) stone fruit breeding program at Byron, GA, is one of the few public programs that remain active in developing new peach cultivars adapted to the southeastern climate and suitable for the regional shipping industry. The “prince” series peach cultivars, most of which produce large, firm, melting, freestone fruit with yellow flesh, normal acidity, and high blush, were released to meet this need (Okie, 1993; Okie and Layne, 2008a, 2008b; Okie et al., 1982; Okie and Reilly, 1987). As a continuation of this effort, ‘Crimson Joy’ (tested as BY99P3866) is released, along with two other “Joy” cultivars (Chen and Okie, 2020a, 2020b). This cultivar has a chilling requirement estimated at ≈700 chill hours (CH) and is suited for areas with medium to high chill accumulation. ‘Crimson Joy’ is well adapted to the southeastern climate, has performed well in Georgia and South Carolina, and is suggested for trial wherever ‘GaLa’ or ‘Harvester’ are grown.

Florida Peach and Nectarine Varieties

The Florida stone fruit breeding program began in 1952, under the direction of Dr. Ralph Sharpe. The major goal of Dr. Sharpe’s breeding program was to take advantage of the climate in Florida to provide early, high-quality fruit to the market (Sherman et. al., 1996). In 1966, Dr. Wayne Sherman became the leader of the stone fruit breeding program, and he continued to focus on breeding for low-chill peach cultivars with non-melting flesh that perform well in Florida’s subtropical climate. The current stone fruit breeder, Dr. Jose Chaparro, has overseen and initiated research to bring in unique plant material that focuses on large, high-quality fruit with disease resistance and low chilling requirements. Peaches and nectarines are the same species, Prunus persica, but nectarines differ from peaches in that they lack “peach fuzz.” Therefore, the following discussion applies to both peaches and nectarines, but in most cases reference will be made only to peaches. This 17-page publication is a minor revision written by Ali Sarkhosh, Mercy Olmstead, Jose Chaparro, Pete Andersen, and Jeff Williamson, and published by the Horticultural Sciences Department, October 2018. Cir1159/MG374: Florida Peach and Nectarine Varieties (ufl.edu)

Growing Plums in Florida

Plums could be a potential crop for growers and homeowners in Florida and other mild winter areas throughout the Gulf coast, but many plum varieties from the west coast will not consistently perform well enough in Florida to produce fruit. However, the University of Florida's stone fruit breeding program has developed cultivars that improve the potential for growing plums in Florida and other mild winter areas that have high disease pressure. These cultivars are recommended for trial in Florida. The names of all University of Florida plum cultivars begin with the prefix 'Gulf.' These cultivars are Japanese type plums (Prunus salicina Lindl.) and have resistance to plum leaf scald (Xylella fastidiosa) and bacterial spot (Xanthomonas campestris). Fruit size is satisfactory (about 1½ to 2 inches in diameter) with good fruit quality. They ripen in early to late May, approximately two weeks before plums from other areas arrive in the marketplace. This 13-page publication is a minor revision written by A. Sarkhosh, M. Olmstead, E. P. Miller, P. C. Andersen, and J. G. Williamson, and publsihed by the Horticultural Sciences Department, September 2018. HS895/HS250: Growing Plums in Florida (ufl.edu)

Florida Peaches: A Perfect Snack

For many years peach orchards were limited to geographic areas with an adequate number of hours below 45 degrees Fahrenheit, during the colder months, also known as “Chill hours” (University of Florida, Institute of Food and Agricultural Sciences, 2017). In 1952, a stone fruit breeding program started at the University of Florida with a goal of breeding trees which would produce peaches and nectarines to grow in Florida (Olmstead, Chaparro, Anderson, Williamson, & Ferguson, 2016). In recent decades, horticulturalists have developed peach varieties requiring fewer chill hours. This trait now allows peaches to be commercially produced in Florida (Olmstead et al., 2016). Growing peaches in Florida has been identified as a practical option for citrus farmers who have lost groves to citrus greening. As a result, much of the peach production in Florida is centralized areas where citrus was once prevalent, Central and South Central Florida. However, there are also some peach orchards in North and North Central Florida (Olmstead et al., 2016).
 
 The growing conditions in Florida, have given Florida peaches unique characteristics that make them an ideal spring-time snack. In this document, we will discuss the unique Florida peach, including its smaller size, seasonality, tree-ripened sweetness, and health benefits. Lastly, we will leave you with recommendations to keep your Florida peaches fresh as long as possible.

Genetic diversity in peach [Prunus persica (L.) Batsch] at the University of Florida: past, present and future

The University of Florida (UF) stone fruit breeding and genetics program was created in 1952 to develop early ripening stone fruit cultivars with high quality, adaptation to summer rainfall, low chilling requirements, and the ability to withstand high disease pressure. Diverse germplasm sources were used to introduce desirable traits in UF breeding pool. The main objective of this research was to determine the genetic diversity and population structure of the breeding germplasm, and to search for loci under selection. A total of 195 peach genotypes were used: UF cultivars and advanced selections (n = 168), cultivars and selections from the UF-UGA-USDA joint breeding effort (n = 13), landrace cultivars (n = 4), high-chilling cultivars released by NCSU (n = 5), and related Prunus (n = 5) species. A total of 36 SSR markers distributed across the peach genome amplified 423 alleles. An average of 18 genotypes were detected per marker: A (number of observed alleles) of 11.43, Ae (effective number of alleles) of 2.58, Ho (observed heterozygosity) of 0.4, He (expected heterozygosity) of 0.52, F (Wright’s fixation index) of 0.25, and PIC (polymorphism information content) of 0.48. UPGMA cluster analysis based on Nei’s genetic distance represented best the known pedigree information for the germplasm pools. Two major groups were observed across the germplasm corresponding to melting and non-melting flesh cultivars/selections. Population structure results supported these two major groups. Several loci closely located to genome regions where different phenotypic traits have been previously mapped were detected to be under selection.

TexFirst, an Early-ripening, Low-chill Peach for the Subtropics

This peach tree [Prunus persica (L.) Batsch] originated in the Stone Fruit Breeding Program at Department of Horticultural Sciences at Texas A&M University, located in College Station, TX. The seed parent was the Thai Tiger peach TXW1193-1 (Byrne and Boonprakob, 2008), a cultivar jointly released by Texas A&M University and Kasetsart University (Kampangsaen, Nakhonpathom, Thailand). Open-pollinated seed from Thai Tiger TXW1193-1 was planted in a highdensity fruiting nursery at College Station in 1996. From this progeny, the seedling denominated as TX1A95 was selected for its early maturity, good productivity, yellow ground color, round shape, high red overcolor, and excellent firmness. It was propagated asexually by budding and has been evaluated in Texas and California.

Check Digits for Detecting Recording Errors in Horticultural Research: Theory and Examples

Check digit technology is frequently used in commercial applications such as shipping labels and credit cards to flag errors in numbers as they are used. Most systems use modular arithmetic to calculate a check digit from the digits in the identification number. Check digits are little used in horticultural research because the guidelines for implementing them are neither well known nor readily accessible. The USDA–ARS stone fruit breeding program at Byron, Ga., plants thousands of trees annually, which are identified using a 2-digit year prefix followed by a sequential number that identifies the tree location in the rows. Various records are taken over the life of the tree including bloom and fruit characteristics. Selected trees are propagated and tested further. To improve the accuracy of our records we have implemented a system which uses a check number which is calculated from the identification number and then converted to a letter that is added onto the end of the identification number. The check letter is calculated by summing the products of each of the digits in the number multiplied by sequential integers, dividing this sum by 23, and converting the remainder into a letter. Adding a single letter suffix is a small change and does not add much complexity to existing data collection. The types of errors caught by this system are discussed, along with those caught by other common check digit systems. Check digit terminology and theory are also covered.

PROGRESS AND PROSPECTS IN STONE FRUIT BREEDING

PROGRESS AND PROSPECTS IN STONE FRUIT BREEDING

THE ITALIAN NATIONAL PEACH BREEDING PROJECT

In 1994 the Ministry for Agricultural and Forestry Policy (Mi.P.A.F.) has financed a national research program named “Fruit Growing”, coordinated by the Istituto Sperimentale per la Frutticoltura (ISF) and composed of several projects relevant to stone fruit breeding, pome fruit breeding, rootstock breeding, strawberry breeding, tree training, post harvest, and marketing. Working groups on peach are active within the stone fruit and rootstock breeding projects. The main objectives of the breeding programs were: improved fruit quality, resistance or tolerance to diseases and pests (both for scions and rootstocks), suitability for difficult soils (for rootstocks). Nine units, belonging to Mi.P.A.F. (Fruit Tree and Plant Pathology Research Institutes) and University (Bologna, Florence and Pisa), were involved. Up to now, 7 peach cultivars, 1 nectarine and 2 rootstocks have been commercially released and several scion advanced selections are under evaluation for brown rot, leaf curl, green aphid resistance or tolerance, and rootstock selections for chlorosis, asphixya, nematodes, Armillaria and Phytophthora resistance or tolerance.

Developing a quantitative method to evaluate peach (Prunus persica) flesh mealiness

A quantitative method to measure peach flesh mealiness based on free juice was developed. Free juice was measured by subjecting fruit tissue to a pressing force of 667 N for 1 min before centrifugation. After this extraction, the juice was collected and centrifuged at 6000g for 10 min. The supernatant was weighed and used to represent the free juice from the total initial tissue. The percentage of free juice was more sensitive and it had a higher correlation to mealiness measured visually and by a trained panel than the extractable juice method. Our work also demonstrated that trained judges were able to perceive mealiness earlier than visual mealiness symptoms were expressed. This free juice measurement provides an objective and accurate method to evaluate mealiness potential of stone fruit breeding lines and fruit biochemical and/or physiological changes during postharvest storage. © 2002 Elsevier Science B.V. All rights reserved.

Three New Peaches and a Nectarine for the Southeastern United States

Four new varieties have been released from the USDA–ARS Stone Fruit Breeding program located in central Georgia. All are adapted to the humid Southeastern U.S. climate. `Rubyprince' is an early yellow-fleshed peach with excellent size, firmness, and color. The slow-softening fruit ripens in early June at Byron, about with `Dixired', but is slightly lower chilling (about 800 h below 45 °F). `Blazeprince' is a very firm yellow-fleshed peach with a solid red blush that ripens in late mid-season between `Harvester' and `Redglobe'. It is susceptible to bacterial spot disease similar to `O'Henry'. It requires about 850 chill hours. `Southern Pearl' is a large white-fleshed, mid-season peach with very good acid flavor and medium firmness. It ripens about with `Harvester' or `Redhaven'. Chilling requirement is only about 650 h, similar to `Springcrest'. `Juneprincess' nectarine ripens in about the same season as `Southern Pearl' and produces large, attractive, firm fruit that is less prone to rain cracking than many nectarines. Skin color is bright red, typical of California nectarines, with yellow flesh. Chilling requirement is about 850 h.

`Black Ruby', a Japanese-type Plum Adapted to the Humid Southeastern United States

`Black Ruby' is the newest plum released by the USDA stone fruit breeding program at Byron. This variety has large, firm fruit that ripens in early July, about 1 week after `Santa Rosa'. Fruit has reddish-black skin and yellow flesh. Eating quality is very good. `Black Ruby' has an upright tree similar to `Santa Rosa', except that tree health and vigor are much better than `Santa Rosa'. USDA has been breeding plums for the humid Southeast for 30 years. Goals are to combine large, firm, high-quality fruit with a disease-resistant tree that will live 8 to 10 years. Most plum varieties are short-lived in our area due to disease caused by Xanthomonas, Pseudomonas, and Xylella. Most existing varieties adapted to our climate have fruit unsuitable for commercial production. Previous USDA releases include “green plum” types `Robusto' (1980) and `Segundo' (1984); a yellow plum, `Byrongold' (1985); a black shipping plum, `Explorer' (1980); and the blood-fleshed, high-quality `Rubysweet' (1989).

`Black Ruby', a Japanese-type Plum Adapted to the Humid Southeastern United States

`Black Ruby' is the newest plum released by the USDA stone fruit breeding program at Byron. This variety has large, firm fruit that ripens in early July, about 1 week after `Santa Rosa'. Fruit has reddish-black skin and yellow flesh. Eating quality is very good. `Black Ruby' has an upright tree similar to `Santa Rosa', except that tree health and vigor are much better than `Santa Rosa'. USDA has been breeding plums for the humid Southeast for 30 years. Goals are to combine large, firm, high-quality fruit with a disease-resistant tree that will live 8 to 10 years. Most plum varieties are short-lived in our area due to disease caused by Xanthomonas, Pseudomonas, and Xylella. Most existing varieties adapted to our climate have fruit unsuitable for commercial production. Previous USDA releases include “green plum” types `Robusto' (1980) and `Segundo' (1984); a yellow plum, `Byrongold' (1985); a black shipping plum, `Explorer' (1980); and the blood-fleshed, high-quality `Rubysweet' (1989).

A Pedigree Tracing Program for Use with dBASE III and dBASE IV Software

Breeding programs maintain extensive pedigree files for genetic studies, determination of coancestry coefficients, planning crosses, and quick reference (Barr, 1983; Bell et al., 1980; Byrne, 1989; Scorza et al., 1985). This information is also used to trace pedigrees and produce graphic lineages. The tracing of a pedigree from a large file is often done by hand or with a mainframe computer (Bell et al., 1980; Scorza et al., 1985). The process, although not complex, can be cumbersome and inconvenient. There is a trend now to use microcomputers with large-capacity storage media (e.g., hard disks) that can store extensive data files. With them, researchers have the advantage of being able to interact with the computer in a more convenient and efficient manner using sophisticated, menu-driven software packages. Researchers at the Stonefruit Breeding Program, Texas A&M Univ., have developed a computer program named “PED” in the dBASE III/dBASE IV (Ashton-Tate Corp., Torrance, Calif.) programming language that searches a dBASE pedigree data file and quickly produces a four-generation graphic family tree (Fig. 1) on the screen or for printing (Liskin, 1986). Pedigree data are

THE EFFECTS OF MILD WINTER WEATHER CONDITIONS ON PEACH FRUIT SHAPE

Mild winter weather conditions reduce fruit yield and quality of many peach cultivars grown in the Medium Chill Region of the United States. Peach fruit shape instability limits marketing options for growers in this region. The Stonefruit Breeding Program at Texas A&M University evaluated a wide range of peach cultivars and breeder selections from throughout the world during the mild winters of 1988-198 9 and 1989-1990. Fruit shape response was highly variable among genotypes with similar chilling requirements. The implication of this is that the potential is high for eliminating fruit shape instability due to highly variable winter conditions in the Medium Chill Peach Production Region.