Phloridzin is a phenolic compound unique to apple (Malus domestica (Suckow) Borkh.) and its wild relatives. Since its discovery, phloridzin has been researched for its nutraceutical properties, including anti-diabetic, anti-cancer, and antioxidant activities, making phloridzin a potential target for nutritional improvement in new apple cultivars. However, phloridzin accumulates at significantly lower concentrations in fruit than in vegetative tissues and seeds. In ‘Golden Delicious’ and its sports, we observed higher phloridzin content in peels of sports with a cuticle disorder termed russet. In russeted apples, the smooth, waxy fruit cuticle is partially or entirely replaced by a corky layer, induced through environmental and genetic effects. To understand the variation of phloridzin content and fruit russet in apple fruit, we surveyed 108 accessions with variation in russeting from the USDA-ARS Malus germplasm collection in Geneva, NY. Russeting in apple fruit ranged from 0 to 100%, and phloridzin content ranged from 24.3 to 825.0 μg/g in peels. Mean phloridzin content varied significantly between russeting groups; in groups with light (0–5%), medium–high (70–80%), and high (90–100%) russeting mean phloridzin content was 115.2, 591.2, and 378.8 μg/g, respectively. We observed that genetic factors and russeting are strong predictors of phloridzin content in peels, but not fruit flesh or leaves. Conversely, other peel phenolics are negatively associated with russeting. We observed variable phloridzin content related to russet incidence during fruit development in ‘Golden Delicious’ (low to medium russet) and its sports, ‘Empress Spur’ (low russet), ‘Razor’ (complete russet), and ‘Sergeant Russet’ (medium to high russet).

Dihydrochalcones (DHCs) are a distinctive characteristic of Malus species, with phloridzin as the major DHC in most Malus species, including cultivated apple. DHCs in apple have unique chemical properties with commercial and nutritional value and may yield important insights into the evolution and physiology of apple. A few species produce sieboldin and trilobatin instead of phloridzin, and interspecific hybridization produce offspring with combinations of phloridzin, sieboldin, and trilobatin. Using Malus prunifolia PI 89816 as a common male parent, five F1 populations were developed to understand the genetic basis of these DHCs in Malus. We measured DHC content in each population and observed segregation into five distinct DHC profiles, which fit a model for three independently segregating loci. QTL associated with DHC content were identified on linkage groups 7 and 8 of the Malus genome using linkage analysis with a cross of NY-152 by M. prunifolia PI 589816 and association mapping with a Malus germplasm collection. In addition to DHC segregation, we observed variation in the relative proportions of phloridzin, sieboldin, and trilobatin. The QTL identified represent a critical step in understanding the genetic controllers of DHC content in Malus.

Dihydrochalcones, beneficial phenolic compounds, are abundant in Malus Mill. species, particularly in vegetative tissues and seeds. Phloridzin (phloretin 2′-O-glucoside) is the primary dihydrochalcone in most Malus species including cultivated apple, Malus × domestica Borkh. A few species contain sieboldin (3-hydroxyphloretin 4′-O-glucoside) or trilobatin (phloretin 4′-O-glucoside) in place of phloridzin, and interspecific hybrids may contain combinations of phloridzin, sieboldin, and trilobatin. Proposed health benefits of phloridzin include anti-cancer, antioxidant, and anti-diabetic properties, suggesting the potential to breed apples for nutritional improvement. Sieboldin and trilobatin are being investigated for nutritional value and unique chemical properties. Although some of the biosynthetic steps of dihydrochalcones are known, little is known about the extent of variation within Malus germplasm. This research explores the genetic diversity of leaf dihydrochalcone content and composition in Malus germplasm. Dihydrochalcone content was measured using high performance liquid chromatography (HPLC) from leaf samples of 377 accessions, representing 50 species and interspecific hybrids from the USDA-Agricultural Research Service (ARS) National Plant Germplasm System Malus collection. Within the accessions sampled, 284 accessions contained phloridzin as the primary dihydrochalcone, one had only trilobatin, two had phloridzin and trilobatin, 36 had sieboldin and trilobatin, and 54 had all three. Leaf phloridzin content ranged from 17.3 to 113.7 mg/g with a heritability of 0.76 across all accessions. Beyond the potential of dihydrochalcones for breeding purposes, dihydrochalcone composition may be indicative of hybridization or species misclassification.

Apple (Malus × domestica Borkh.) is one of the top three US fruit crops in production and value. Apple production has high costs for land, labor and inputs, and orchards are a long-term commitment. Production is dominated by only a few apple scion and rootstock cultivars, which increases its susceptibility to dynamic external threats. Apple crop wild relatives, including progenitor species Malus sieversii (Ledeb.) M. Roem., Malus orientalis Uglitzk., Malus sylvestris (L.) Mill., and Malus prunifolia (Willd.) Borkh., as well as many other readily hybridized species, have a wide range of biotic and abiotic stress resistances as well as desirable productivity and fruit quality attributes. However, access to wild materials is limited and wild Malus throughout the world is at risk of loss due to human encroachment and changing climatic patterns. The USDA-ARS National Plant Germplasm System (NPGS) Malus collection, maintained by the Plant Genetic Resources Unit in Geneva, NY, US is among the largest collections of cultivated apple and Malus species in the world. The collection currently has 5004 unique accessions in the field and 1603 seed accessions representing M. × domestica, 33 Malus species, and 15 hybrid species. Of the trees in the field, 3,070 are grafted and are represented by a core collection of 258 individuals. Many wild species accessions are represented as single seedlings (non-grafted). The crop vulnerability status of apple in the US is moderate because although there are a few breeders developing new commercial cultivars who also access Malus species, threats and challenges include new diseases, pests, and changing climate combined with industry needs and consumer demands, with a limited number of cultivars in production.

Despite the demonstrated importance of gibberellins (GAs) as regulators of fruit tree stature, information on their in vivo metabolism in apple vegetative tissues is still lacking. To determine whether the GA content and metabolism differs between dwarf and standard phenotypes and the influence of rootstocks, [ 14 C]GA 12, a common precursor of all GAs in higher plants , was applied to vigorously growing apple ( Malus ×domestica ) shoots collected from the scion cultivar Redcort on MM.106, a growth-promoting rootstock, and dwarf and standard seedlings on their own roots from progeny 806 (a cross between a breeding selection with reduced stature and an advanced breeding selection with a standard tree form). Twenty-one metabolites were identified by high-performance liquid chromatography (HPLC) and used as tracers for the purification of endogenous GAs. The existence of endogenous and [ 2 H]-labeled GA 12 , GA 15 , GA 53 , GA 44 , GA 19 , GA 20 , and GA 3 was demonstrated by gas chromatography–mass spectrometry (GC-MS); GA 20 was the major GA present, with slightly less GA 19 and GA 44 , and with GA 3 present at approximately one-third the level of GA 20 . Despite specific searching, neither GA 4 , GA 7 , GA 1 , nor GA 29 was found, showing that [ 14 C]GA 12 is metabolized mainly through the 13-hydroxylation pathway and that GA 3 is a bioactive GA in apple vegetative tissues. The invigorating rootstock led to a slow GA metabolic rate in ‘Redcort’. For self-rooted plants, the same GAs were identified in dwarf and standard seedlings from progeny 806, although standard plants metabolized at twice the speed of dwarf plants. Young branches of dwarf 806 plants treated with GA 3 were one-third longer with more nodes but similar in internode length. We conclude that the dwarf phenotype in progeny 806 is not caused by a lack of certain GAs in the GA biosynthesis pathway downstream of GA 12 .

The USDA - Specialty Crop Research Initiative-funded RosBREED project is focused on enabling marker-assisted breeding in the Rosaceae. New molecular tools for selection need to be developed before this technology will be widely accepted and applied to apple breeding programs. As well as detailed genotypic data of interrelated progenies, parents and ancestor cultivars, fully descriptive phenotypic data also need to be collected. For apple, fruit phenotyping begins at harvest, followed by 10 and 20 weeks regular storage, each followed by 7 days shelf life at room temperature. The standardized phenotyping protocols agreed by breeding teams in Washington, Minnesota and New York states will be presented in this paper.

The modulus and breaking strength of the skins of different apples were measured: McIntosh, Red Delicious, and Empire stored under controlled atmosphere; McIntosh stored at 1.7°C without atmospheric control, and Honey Crisp and Crimson Gala grown under light and heavy crop conditions. The moduli of the skins of Honey Crisp and Crimson Gala were lower (P < 0.05), than those of Empire, McIntosh, and Red Delicious. Peak puncture force values of McIntosh, Red Delicious, and Empire were lower (P < 0.05) than those of Crimson Gala and Honey Crisp; the contribution of the skin of the Honey Crisp apples to the peak force was least among all the studied apples.

The plant family Rosaceae consists of over 100 genera and 3,000 species that include many important fruit, nut, ornamental, and wood crops. Members of this family provide high-value nutritional foods and contribute desirable aesthetic and industrial products. Most rosaceous crops have been enhanced by human intervention through sexual hybridization, asexual propagation, and genetic improvement since ancient times, 4,000 to 5,000 B.C. Modern breeding programs have contributed to the selection and release of numerous cultivars having significant economic impact on the U.S. and world markets. In recent years, the Rosaceae community, both in the United States and internationally, has benefited from newfound organization and collaboration that have hastened progress in developing genetic and genomic resources for representative crops such as apple (Malus spp.), peach (Prunus spp.), and strawberry (Fragaria spp.). These resources, including expressed sequence tags, bacterial artificial chromosome libraries, physical and genetic maps, and molecular markers, combined with genetic transformation protocols and bioinformatics tools, have rendered various rosaceous crops highly amenable to comparative and functional genomics studies. This report serves as a synopsis of the resources and initiatives of the Rosaceae community, recent developments in Rosaceae genomics, and plans to apply newly accumulated knowledge and resources toward breeding and crop improvement.

A multi-site experiment to evaluate the performance of 23 apple (Malus x domestica Borkh.) cultivars was established in 1999. The purpose was to evaluate new and promising cultivars and breeding selections in a range of geographical and climatic areas within North America. All trees were propagated on M.9T337 and minimally pruned to encourage early bearing. 'Pinova' and 'Cripp's Pink' had the most flower clusters in the first year after planting. At the end of the fifth growing season 'Cripp's Pink' trees were among the largest while NY 65707-19 and 'Minnewashta' were the smallest. CQR10T17 and 'Golden Delicious' had the greatest cumulative yield. 'Pinova' had the highest yield efficiency and highest mean number of fruit per year. The largest fruit were produced on NY 75907-49. Three breeding selections NJ 90, NY 65707-19 and NY 75907-49 had pre-harvest fruit drop in excess of 20%. 'Chinook' had the heaviest annual crop load but also had the smallest fruits. 'Minnewashta' and 'Silken' were the earliest blooming cultivars while 'Runkel' bloomed the latest. Across all sites the average days from bloom to harvest was 184 days for 'Cripp's Pink' making it the latest cultivar to mature and probably not suited to be grown in more northern regions of the continent.

The NE-183 regional project was established in 1994 with its primary objective to evaluate horticultural characteristics and pest susceptibility of new apple (Malus x domestica Borkh.) cultivars and advanced selections at numerous locations throughout the United States and Canada to determine both limitations and positive attributes of these cultivars. The project was established because many new apple cultivars were available but there was no established mechanism to provide unbiased evaluation to aid orchardists in making informed decisions about what apple cultivars have the greatest likelihood of being successful. There were two types of plantings: horticulture and pest susceptibility. Pest susceptibility plantings were intended to assess natural susceptibility of cultivars to insects and diseases. The horticulture plantings were intended to evaluate horticultural characteristics, fruit quality and sensory characteristics of the cultivars. The first NE-I 83 cultivar planting was established in 1995 at 28 locations in 18 states or Canadian provinces. A second group of 23 cultivars was planted in 1999. This article summarizes the rationale for initiating the NE-183 project, and lists the cultivars, locations and overall project design for the 1999 planting.