Location: Plant Genetic Resources Unit (PGRU)Title: Genetic diversity of dihydrochalcone content in Malus germplasm
Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2018
Publication Date: 4/7/2018
Citation: Gutierrez, B.L., Brown, S., Zhong, G., Chao, C.T. 2018. Genetic diversity of dihydrochalcone content in Malus germplasm. Genetic Resources and Crop Evolution. 65(5):1485-1502.
Interpretive Summary: Phloridzin is an important nutritional compound produced in apple peels and vegetative tissues. We surveyed apple accessions from the Plant Genetic Resources Unit (PGRU) Malus collection, and observed a broad range of concentrations of 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 apples. 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: The dihydrochalcone phloridzin (phloretin 2'-O-glucoside) is abundant in Malus (Mill.) species including the cultivated apple, M.×domestica (Borkh.). Phloridzin has health benefits including anti-cancer, antioxidant, and anti-diabetic properties. Phloridzin has potential in breeding for apple nutritional improvement. While the biosynthetic steps of phloridzin are known, little is known about its genetics or biochemical regulation. This research explores the genetic diversity of phloridzin content in Malus germplasm. Phloridzin content was measured using High Performance Liquid Chromatography (HPLC) in leaf samples for three years in 345 accessions, representing 29 species and 16 interspecific hybrids from the USDA Malus germplasm collection. Leaf phloridzin content ranged from 17.3 to 113.7 mg/g and genotype accounted for 62% of the observed variation. Between-year correlations were high (r = 0.70), indicating seasonal stability. In addition to phloridzin, the dihydrochalcones sieboldin (3-hydroxyphloretin 4'-O-glucoside) and trilobatin (phloretin 4'-O-glucoside) were detected in certain accessions. These compounds distinguish some Malus species, with sieboldin or trilobatin replacing phloridzin in some accessions. Within the collection sampled, 274 accessions (79%) contained phloridzin as the primary dihydrochalcone, 29 (8%) contained sieboldin and trilobatin, and 44 (13%) contained phloridzin, sieboldin, and trilobatin. Extensive qualitative and quantitative variation in dihydrochalcone content was identified in this germplasm survey.