Varietal Differences in the Flavonol Content of Mulberry (Morus spp.) Leaves and Genetic Analysis of Quercetin 3-(6-Malonylglucoside) for Component Breeding

The varietal differences in the flavonol glycosides rutin, isoquercitrin, kaempferol 3-(6-rhamnosylglucoside), quercetin 3-(6-malonylglucoside), astragalin, quercetin 3-(6-acetylglucoside), and kaempferol 3-(6-malonylglucoside) contained in mulberry leaves were elucidated. This information was used for breeding mulberry cultivars with a high concentration of functional components. The flavonol content, composition, and proportion in leaves varied widely. 'Kobuchizawa 1' had the highest level of total flavonols (1819 mg/100 g of dry weight), 5 times higher than that of 'Mikurasima 15' (393 mg/100 g of dry weight). Quercetin 3-(6-malonylglucoside) was the most abundant flavonol, although it was not found in all cultivars. Quercetin 3-(6-acetylglucoside) was only found in 'Keguwa'. From the quercetin 3-(6-malonylglucoside) content in crossbred offspring, malonyltransferase, an enzyme involved in quercetin 3-(6-malonylglucoside) synthesis, was acquired according to Mendelian inheritance. An offspring with a higher quercetin 3-(6-malonylglucoside) level than both parents was obtained from the crossing. This suggested that crossbreeding was effective for acquiring cultivars with a higher content of quercetin 3-(6-malonylglucoside).