Genetic Diversity of Dihydrochalcone Content in Malus Germplasm

The dihydrochalcone phloridzin (phloretin 2ʹ-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 4ʹ-O-glucoside) and trilobatin (phloretin 4ʹ-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.