Tree vegetative and generative properties and their inter-correlations for prospective apple cultivars under two training systems for young trees

Little information is available on vegetative and generative performance of apple cultivars during the early growth of trees in orchards. The aim of this five-year study was to evaluate 2 vegetative (trunk cross sectional area (TCSA) and tree height (TH)) and 7 generative parameters (tree yield (TY), fruit number per tree (FNT), crop load (CL), fruit diameter (FD), shape index (SI), fruit surface color (FSC) and fruit color intensity (FCI)) and their inter-correlations (Pearson correlation, regression analyses and PCA) for young apple trees, on 9 apple cultivars (‘Jugala’, ‘Galaval’, ‘Gala Venus Fengal’, ‘Gala Decarli-Fendeca’, ‘Gala Schnitzer (S) Schniga’, ‘Fuji September Wonder’, ‘Crimson Crisp (Co-op 39)’, ‘Jeromine’, and ‘Red Idared’) in a slender spindle training system (2597 trees ha−1) and on 4 apple cultivars (‘Wilton’s Red Jonaprince’, ‘Red Cap Valtod (S)’, ‘Early Red One’, and ‘Red Topaz’) in a super spindle training system (5194 trees ha−1) in Eastern Hungary. The strongest vegetative growth was observed in ‘Red Idared’, while the weakest was in ‘Early Red One’. Most ‘Gala’ mutants showed high yields in all years, except for ‘Galaval’. On the 6 year-old trees, the lowest tree yield was found in ‘Fuji September Wonder’ (8.2 kg tree−1), while the highest was found in ‘Gala Venus Fengal’ (35.8 kg tree−1). The lowest fruit number per tree (15 fruit tree−1) was found in ‘Jeromine’, while the highest (222 fruit tree−1) was in ‘Gala Venus Fengal’. The highest crop load was found in ‘Gala Venus Fengal’ (12.72 fruit per cm2 TCSA), while the lowest was in ‘Jeromine’ (2.13 fruit per cm2 TCSA). The smallest fruit diameter (66.3 mm) was recorded in ‘Gala Schnitzer (S) Schniga’, while highest (93.6 mm) was in ‘Red Idared’. The lowest shape index (0.73) was found in ‘Red Topaz’, while the highest (0.92) was in ‘Red Idared’. The majority of the cultivars reached very good fruit surface color (80–100%). The lowest fruit surface color (40%) was observed in ‘Gala Schnitzer (S) Schniga’, while the highest (100%) was in ‘Jeromine’ and ‘Early Red One’. The highest fruit color intensity was observed in most cultivars with the exception of ‘Jeromine’, ‘Gala Schnitzer (S) Schniga’ and’Fuji September Wonder’. In addition, correlation and regression analyses revealed strong and significant (p = 0.05) relationships between TH vs TCSA, TY vs TCSA, TH vs TY, TY vs FNT, and FCI vs FSC. PCA explained 87% of the total variance and PC1, PC2, PC3, and PC4 accounted for 33, 21, 20, and 13% of the variance, respectively, and correlated with TSCA, TH, TY and FNT; with FNT, CL and FS; with FSC and FCI; and with TH and SI, respectively. In conclusion, our study provides useful tree property data on prospective mutants/cultivars for growers/advisors in order to select the most suitable cultivars for establishing new orchards under climate conditions similar to central Europe.