Effect of Rootstocks and Irrigation Rate on Vigor and Productivity of Sweet Cherry

The commercial adoption of relatively new rootstocks such as Gisela and Grand Manil (GM) has been limited in Bulgaria sweet cherry (P. avium L.) industry despite their ability to induce precocity and reduce scion vigor compared to the standard Mazzard (P. avium L.). These trees are frequently more vulnerable to various stressors and especially to the dryness of soil. For this reason, many cherry growers have focused on the construction of irrigation systems. The influence of Gisela 5, GM61/1, GM79 and GM9 rootstocks and irrigation rate onto vegetative growth, yield and quality of 'Burlat', 'Regina' and 'Bing' sweet cherry cultivars was studied during six years after grafting. The experiment was performed at the Fruit Growing Institute (Plovdiv, Bulgaria), on an alluvial-meadow soil (Fluvisol). The trees were planted at 5 m x 3 m (667 trees/ha). Two irrigation regimes were examined during the growing season: 100 and 50 % of the estimated crop evapotranspiration (ETc). The trees on Gisela 5 and GM 79 responded the most obviously to experimental irrigation rates. It was found that trunk cross sectional area and canopy volume of the trees grown in water deficit conditions were significantly lower than those in 100 % ET. Irrigation of trees on GM61/1 and GM 9 had no significant influence on the ranking of cultivar vigor. Among rootstocks, cumulative yield per tree was highest with Gisela 5 and lowest with GM 9. However, the cumulative yield on Gisela 5 was lower when applying deficit irrigation, in comparison with optimal irrigation regime (100 % ET).