Location: Plant Genetic Resources Unit (PGRU)Title: Increased Phloridzin content associated with russeting in apple fruit
Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2018
Publication Date: 8/21/2018
Citation: Gutierrez, B.L., Zhong, G., Brown, S. 2018. Increased Phloridzin content associated with russeting in apple fruit. Genetic Resources and Crop Evolution. 65(8):2135-2149.
Interpretive Summary: Phloridzin is an important nutritional compound produced in apple peels and vegetative tissues. Article highlights a germplasm survey of apple accessions from the PGRU Malus collection. We observed a broad range of concentrations for phloridzin from apple fruit and leaves. From our survey we identified an association between phloridzin content and a peel disorder termed russeting; when peels russet, phloridzin content increases. We describe the chemical variation associated with russeting in apple. Currently, little is known about how phloridzin is regulated in apple; some genes associated with biosynthesis are known, and nothing has been reported about what may cause concentrations to vary between tissue types. Our results identified genetic resources which could be used for further biochemical and genetic studies into phloridzin. Additionally, we propose that genes associated with apple russeting should be investigated as regulators of phloridzin content. A greater understanding of the genetic controls of phloridzin could lead to nutritionally enhanced apple cultivars.
Technical Abstract: Phloridzin is a phenolic compound, unique to apple (Malus ×domestica 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. We observed that genetic factors and russeting are strong predictors of phloridzin content in peels, but not fruit flesh or leaves. Other peel phenolics are negatively associated with fruit russeting in apple. Following changes in phloridzin content 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), we observed variable phloridzin content related to russet incidence.