Vegetative and productive performances of 'Kordia' and 'Regina' sweet cherry cultivars grafted on four clonal rootstocks in the Alpe Adria region

The sweet cherry rootstock experiment was conducted in six locations in the Alpe Adria region: Verona and Sondrio (Italy), Bilje and Maribor (Slovenia), Haidegg (Austria) and Zagreb (Croatia). Four clonal rootstocks (‘Gisela^® 5’, ‘Gisela^® 6’, ‘Piku 1’, ‘PHL-C’), grafted with ‘Kordia’ and ‘Regina’ cultivars were compared. After eight years of testing, the behaviour of both cultivars showed no substantial differences, even though significant interactions were observed in some parameters, which lead to further analysis of rootstock, location and year effect. None of rootstocks showed superior performance in all parameters. ‘PHL-C’ was the least interesting, as it had the lowest cumulative yield and yield efficiency along with high mortality and the highest sucker formation. In general, a positive correlation between tree vigour and fruit weight was observed. Among other three rootstocks (‘Gisela 5’, ‘Gisela 6’ and ‘Piku 1’), the only significant difference is a significantly lower vegetative growth of ‘Gisela 5’, with the same yield efficiency, fruit weight, cumulative yield and tree mortality compared to ‘Gisela 6’ and ‘Piku 1’. The results show that rootstock 
’Gisela 5’ performs well in good pedoclimatic conditions, while in suboptimal conditions it does not perform so well, thus it is advisable to use ‘Gisela 6’ or ‘Piku 1’ for such locations. High mortality of ‘PHL-C’ was observed on all locations. The results of Sondrio, where tree mortality was the highest, show that none of tested rootstocks was tolerant to replant disorder.