Peach x almond hybrid clones are often used as rootstocks for peach. In the past, DCDSL of Pisa selected the "I.S." series of such clones, which was then tested for many years in the coastal area of Tuscany. Eight clones appeared promising for induced vigour degree and productivity. This paper reports on the results of a comparison between l.S.5 5/8, 5/18, 5/19, 5/21, 5/22 ('Sirio'), 5/23, 5/29, 5/31 and GF 677 (control) clones grafted with 'Suncrest' and planted in 1994 in a fertile soil with medium lime content of the Emilia Romagna region. Trees were planted at 4.5 x 3.0 m spacing and trained to free palmette. Every year, growth and yield parameters were recorded on each of the 12 trees per root stock: trunk cross-sectional area, canopy size, summer and winter pruning weight, number and weight of fruits. During the last two years of measurements, titratable acidity, SSC (º Brix) and flesh firmness were recorded on a sample of 50 fruits per rootstock.
Growth parameters showed that all the I.S. clones were less vigorous than GF 677 according to the following decreasing scale: GF 677 > l.S.5/23 > I.S.5/8 > I.S .5/29 > I.S.5/19 > l.S.5/21 > I.S.5/22 > I.S.5/31 > I.S.5/18. Summer and winter pruning weight was 20-70% higher in GF 677 than in I.S. clones. GF 677 confirmed its high productivity (187 kg/tree cumulated yield), followed by I.S.5/8 and l.S.5/19 clones (170 and 169 kg/tree CY respectively); in contrast, yield efficiency was much higher in less vigorous clones than in GF 677. Specifically, I.S.5/8, I.S.5/19 and I.S.5/22 ('Sirio') were the most efficient rootstocks. Good results for fruit size were achieved in I.S.5/8, I.S.5/18, 'Sirio' and GF 677 (172, 174, 175 and 178 g respectively), followed by I.S.5/29, I.S.5/31 and l.S.5/19 (169 g). 'Sirio', I.S.5/18 and I.S.5/31 also induced an earlier ripening time in 'Suncrest' in comparison to other rootstocks. I.S. clones less vigorous than GF 677 appeared useful to increase planting density while maintaining very high productivity and good fruit quality, and reducing the need for winter and summer pruning to control tree size.