Growth, yield and fruit quality of 'Tropic Snow' peach on size-controlling rootstocks under dry Mediterranean climates

A six-year trial was carried out to evaluate the vegetative and productive performance of low-chill, early-ripening 'Tropic Snow' peach grown on five peach x almond rootstocks, different for their vigor. The study was conducted in south-western Sicily using 45 V-trained peach trees planted in 2005 and grafted on GF677, the most common rootstock in Sicily, and four low-vigor rootstocks selected at the Department of Agricultural, Food and Environmental Sciences, University of Pisa, namely IS 5/8 (Polluce), IS 5/19 (Castore), IS5/23, and IS5/29. Trunk circumference, winter and summer pruning weight, total number and weight of fruits per tree, and major fruit quality traits were recorded starting at the 3rd leaf. After fruit harvest in the 5th leaf, irrigation was withheld during the dry summer period (July-September). All IS selections reduced trunk cross-sectional area (TCSA) and pruning weight compared to GF677, with IS5/23 reducing TCSA by 62% and Castore, Polluce and IS5/29 by 32% by the 8th leaf. Yield efficiency was inversely related to tree vigor, with IS5/23 inducing the highest increase over GF677. Trees on IS5/23 exhibited 24-28% reductions of crop load and yield, whereas only IS5/29 increased fruit size compared to GF677. Postharvest water deficit induced significant yield declines in GF677, IS5/29 and IS5/23 in the following year. Low-vigor trees on Castore, Polluce and IS5/23 were more sensitive to changes in stomatal conductance in terms of carbon fixation, performing better than trees on GF677 and IS5/29 under non-limiting water conditions. Only minor rootstock effects on fruit quality were observed, with IS5/23 reducing significantly the final grower's profit. Overall, all low-vigor rootstocks performed decently, and in particular IS5/29 exhibited a good compromise between growth reduction, yield and fruit size, whereas Castore and Polluce may represent valid alternatives to GF677 for early peach production in dry Mediterranean areas.