Genetic diversity of red-fleshed apples (Malus)

Abstract

Anthocyanins are flavonoid pigments imparting red, blue, or purple pigmentation to fruits, flowers and foliage. These compounds are powerful antioxidants in vitro, and are widely believed to contribute to human health. The fruit of the domestic apple (Malus x domestica) is a popular and important source of nutrients, and is considered one of the top 'functional foods'-those foods that have inherent health-promoting benefits beyond basic nutritional value. The pigmentation of typical red apple fruits results from accumulation of anthocyanin in the skin. However, numerous genotypes of Malus are known that synthesize anthocyanin in additional fruit tissues including the core and cortex (flesh). Red-fleshed apple genotypes are an attractive starting point for development of novel varieties for consumption and nutraceutical use through traditional breeding and biotechnology. However, cultivar development is limited by lack of characterization of the diversity of genetic backgrounds showing this trait. We identified and cataloged red-fleshed apple genotypes from four Malus diversity collections representing over 3,000 accessions including domestic cultivars, wild species, and named hybrids. We found a striking range of flesh color intensity and pattern among accessions, including those carrying the MYB10 R 6 allele conferring ectopic expression of a key transcriptional regulator of anthocyanin biosynthesis. Although MYB10 R 6 was strongly associated with red-fleshed fruit among genotypes, this allele was neither sufficient nor required for this trait in all genotypes. Nearly all red-fleshed accessions tested could be traced back to 'Niedzwetzkyana', a presumed natural form of M. sieversii native to central Asia.

Diversity of polyphenols in the peel of apple (Malus sp.) germplasm from different countries of origin

“…Cyanidin-3-galactoside is essentially present in cultivars with red and partially dark red peels, providing cultivar differentiation for consumers (Boyer & Liu, 2004). The apple flesh is usually colourless, although germplasm does exist where the flesh is highly pigmented (Nocker et al, 2012). This study did not include such red-fleshed cultivars.…”

Breeding depression of red flesh apple progeny containing both functional MdMYB10 and MYB110a_JP genes

“…Nearly all type 1 red flesh varieties including ‘Geneva’ were derived from ‘Niedzwetzkyana’, but the type 2 red flesh ‘Pink Pearl’ could not be traced back to ‘Niedzwetzkyana’ (Van Nocker et al. ). From the phylogenetic analysis, the wild species containing the type 1 red flesh phenotype, such as M. pumila , M. sieversii and M. mandshurica , formed one clade, while type 2 ‘Pink Pearl’ formed another clade with M. × domestica cultivars and M. sylvestris , suggesting that type 1 and type 2 are genetically distinct (Nikiforova et al.…”

“…Ancestry of 'Geneva' and 'Pink Pearl' 'Geneva' and 'Pink Pearl' are chance seedlings of M. pumila 'Niedzwetzkyana' 9 an unknown paternal parent, and 'Surprise' 9 an unknown paternal parent, respectively (Van Nocker et al 2012). Nearly all type 1 red flesh varieties including 'Geneva' were derived from 'Niedzwetzkyana', but the type 2 red flesh 'Pink Pearl' could not be traced back to 'Niedzwetzkyana' (Van Nocker et al 2012).…”

A Major QTL Controlling Earliness of Fruit Maturity Linked to the Red leaf/Red flesh Trait in Apple cv. ^|^lsquo;Maypole^|^rsquo;

“…These fragments showed polymorphism in the progeny of 'Fuji' × 'Maypole'. With regard to alleles derived from 'Maypole', the 496-bp fragment, corresponding to the R6 promoter derived from 'Baskatong' (Nocker et al, 2011), was observed only in the red leaf/red flesh progeny, whereas the 394-bp fragment, derived from 'Wijcik McIntosh', was detected in the green leaf/white flesh offspring (Fig. 2a).…”