Tree growth, productivity and fruit size of 'Čačanska Lepotica' and 'Čačanska Najbolja' plums as influenced by rootstock

From the first to the tenth year after planting the impact of four rootstocks [‘Pixy’, ‘St. Julian A’, ‘Fereley’ and ‘Myrobalan’ seedling (Prunus cerasifera Ehrh.)] on tree vigour (assesed as trunk cros sectional area), yield tree^‑1 and unit area^‑1, cumulative yield, yield efficiency, biennial bearing index and fruit weight of plum cultivars ‘Čačanska Lepotica’ and ‘Čačanska Najbolja’ under Čačak conditions (Serbia) were investigated. Trees were grown under high density planting system and spaced at 4.0×1.8 m (1,380 trees ha^-1). Results showed that ‘Myrobalan’ seedling induced the highest tree vigour of both evaluated cultivars whereas cultivars had the smalest trees on ‘Pixy’. Cultivars grafted on ‘St. Julian A’ and ‘Fereley’ had medium tree vigour. Individually, the most vigorous trees had ‘Čačanska Najbolja’ grafted on ‘Myrobalan’ seedling (106.40 cm²), while ‘Čačanska Lepotica’ grafted on ‘Pixy’ rootstock was vigourless (24.43 cm²). ‘Čačanska Najbolja’on ‘Fereley’ had the highest, while ‘Čačanska Lepotica’ on ‘Pixy’ had the lowest cumulative yield. Biennial bearing index was significantly smaller in ‘Čačanska Lepotica’ than in ‘Čačanska Najbolja’ (0.27 and 0.37, respectively). Regarding rootstocks, values of biennial bearing index varied from 0.31 (‘St. Julian A’ and ‘Fereley’) to 0.37 (‘Pixy’). Fruit weight of ‘Čačanska Najbolja’ was significantly higher than ‘Čačanska Lepotica’. Both cultivars on ‘Pixy’ gave smaller fruits in comparison with ‘Myrobalan’ seedling, ‘St. Julian A’ and ‘Fereley’ with no significant differences among them.