'Star 50' and 'Star 74': New dwarfing grape rootstocks

As part of a breeding programme initiated in 1990 to develop dwarfing stocks for Vitis vinifera, commercial rootstocks under self-or open-pollination led to 400 seedlings, subsequently tested via cuttings for rooting ability and graft compatibility with wine grape 'Cabernet Sauvignon', 'Chardonnay', 'Sangiovese' and table grape 'Muscat de Hambourg'. In a second step, the 'Sangiovese'-grafted cuttings that performed best were tested for vigour and resistance to high concentration of active limestone in comparison with 7 commercial stocks. The 26 best-performing grafted accessions, together with the 7 commercial stocks grafted with 'Sangiovese', were planted in field to test the long-term induced effects on scion. This trial resulted in the selection of two stocks bred by self-fertilisation with 'Binova', a hermaphrodite flower-bud mutation of 'SO4'. The two new stocks were commercially denominated 'Star 50' and 'Star 74'. Both are marked by good vigour control, good lime tolerance and proved capable of controlling 'Sangiovese's excessive cropping while improving its grape composition.