Two new grape cultivars, bud sports of Cabernet Sauvignon bearing pale-coloured berries, are the result of deletion of two regulatory genes of the berry colour locus

Amanda R. Walker, Elizabeth Lee, Simon P. Robinson

Bud sports are infrequent changes in phenotype affecting shoots of woody perennials but the molecular basis of these mutations has rarely been identified. In this report, we show that the bronze-coloured berries of the Malian cultivar, a documented bud sport of the wine grape Cabernet Sauvignon (Vitis vinifera L.), lack anthocyanins in the subepidermal cells compared to the red/black berried Cabernet Sauvignon in which both the epidermis and several subepidermal cell layers contain anthocyanin. The Malian phenotype is correlated with an alteration in the genome indicated by a reduction of hybridisation signal using a MYBA probe. In Shalistin, a white-berried bud sport of Malian, the red allele at the berry colour locus appears to have been deleted completely. These data suggest that Malian could be a L1/L2 periclinal chimera, which gave rise to Shalistin by an invasion of epidermal cells (L1) by the mutated subepidermal cells (L2). The red grape Pinot Noir has given rise to a number of pale coloured sports, although the provenance of the extant sports is not known. We show that a clone of Pinot Blanc (white-berried) does not have a deletion of the red allele of the same dimensions as that in Shalistin, though a small deletion is a likely explanation for the altered phenotype. However, the mechanism of deletion of the red allele of the berry colour locus is a possible means by which other red to white clonal mutations of grapevines have occurred.