Tree vigour and yield of plum grown under high density planting system

During the second through sixth growing seasons, under the environmental conditions of Čačak (Serbia), tree vigour, yield (kg tree^-1 and t ha^-1), yield efficiency, biennial bearing index and fruit weight were studied in five plum cultivars ('Čačanska Rana, 'Čačanska Lepotica', 'Čačanska Najbolja', 'Čačanska Rodna' and 'Stanley') grafted on myrobalan (Prunus cerasifera Ehrh.) seedlings. Trees were planted at a spacing of 4×2 m (1,250 trees ha^-1). Five-year results showed that the final tree vigour, expressed as trunk cross-sectional area (TCSA), was the lowest in 'Čačanska Lepotica' (39.9 cm²) and the highest in 'Čačanska Rana' (75.0 cm²) and 'Čačanska Najbolja' (82.9 cm²). 'Čačanska Rodna' and 'Čačanska Najbolja' gave their first yields as early as the second year (1.08 and 1.47 kg tree^-1, respectively), whereas the first significant yields in all cultivars were obtained in the third year. Cumulative yield was the lowest in 'Čačanska Rana' (30.75 kg tree^-1 and 38.44 t ha^-1), somewhat higher in 'Čačanska Najbolja', 'Čačanska Lepotica' and 'Stanley' (43.86, 60.37 and 73.40 t ha^-1, respectively), and the highest in 'Čačanska Rodna' (66.36 kg tree^-1 and 82.95 t ha^-1). However, 'Čačanska Rodna' had the highest biennial bearing index (0.61), whereas the other cultivars exhibited a moderate or poor biennial bearing habit during the experimental years. The lowest biennial bearing index was recorded in 'Čačanska Lepotica' (0.13). Yield efficiency was the lowest in 'Čačanska Rana' (0.12 kg cm^-2) and highest in 'Čačanska Rodna' (0.41 kg cm^-2). The average fruit weight was in agreement with cultivar-specific traits, and ranged from 27.4 g in 4Čačanska Rodna' to 51.8 g in 'Čačanska Rana'.