Hand fruit thinning was performed for four successive years on 'Gala' apple trees grafted on dwarf P 2 rootstock and planted at a density of 3333 trees/ha. Trees were 5 years old when the experiment started. Three thinning treatments were done with the assumption that apples at harvest should be medium sized (8 fruits per kg), large (7 fruits per kg), or very large (6 fruits per kg). To obtain such results, 84; 74 or 63 fruitlets were left per tree in the beginning of June. Two other treatments included thinning fruitlets with any defects, and no thinning in the control. To avoid subsequent effects of fruit load on blooming intensity, each year new trees were chosen for the experiment. The results indicated that with tree aging fruit load must be decreased to assure the same mean fruit weight.
Colour is traditionally one of the important appearance features of all fruit for consumers in deciding to buy them. Colour is therefore important in the postharvest supply chain. But where does that colour of fruit come from? Clearly the period of growing and the circumstances during growth are important for developing this important feature. During several seasons (2007-2009), the skin colour of individual apples of different cultivars ('Braeburn', 'Fuji', 'Gala', 'Golden Delicious') were measured using a Minolta CR-400 chromameter during the last 40-60 days before (commercial) harvest. By including the biological variation between individual apples in the analyses and applying non linear indexed regression analysis based on process oriented models, explained parts were obtained for the a*-value, all exceeding 90%. The estimated rate constants for the colouration process were remarkably similar for all cultivars (except 'Fuji') and growing conditions. That would indicate that the process of colouration is really reflecting the degradation of chlorophyll and not the production of red or yellow coloured blush (anthocyanins). The expected effect of growing conditions (fertilization and crop level, hail net or not, sunny side or shady side of the tree) did change the mechanism nor the kinetic parameter values but could all be attributed to the minimal obtainable skin colour (asymptotic values of the logistic model). This type of information from the production period may constitute an important link to postharvest supply chain management.
The effect of the subclones of M.9 (M.9 T 337, Pajam 1, RN 29) and the subclones of P 22 (P 22/K, P 22/A, P 22/J), and some of the new Polish rootstocks (P 59, P 60, P 61 and P 62) on the growth and yield of 'Jonagold', 'Ligol' and 'Gala' apple trees was studied in a field experiment over a period of 10 years. The growth vigour of these cultivars on the M.9 subclones was similar to that observed on the standard rootstock M.9 EMLA and among the subclones of P 22, and was similar to those for the standard P 22. Trees of 'Jonagold' grafted on the new Polish rootstock P 62 were significantly less vigorous than those on M.9 EMLA. Trees grafted on P 61 were significantly smaller than the standard trees on P 22. The smallest trees of the tested cultivars were obtained on P 59. In the group of semi-dwarfing rootstocks, the smallest trees were on P 60 and the largest on P 14. The cumulative yields of tested cultivars on the subclones of M.9 were similar to that on standard rootstocks of M.9 EMLA. The cumulative yields of tested cultivars on subclones of P 22 were similar to standard P 22. In the semi-dwarfing group, the highest yields for 'Jonagold' and 'Gala' trees were on P 60 and for 'Ligol' trees on P 14. The values of the yield efficiency index for the subclones of M.9 and new rootstock P 62 were similar to those for M.9 EMLA. Among the subclones of P 22 and new rootstock P 61, the values of this index were similar to those for the standard P 22 rootstocks. The highest yield efficiency index among the semi-dwarfing rootstocks was obtained for P 60. The tested subclones of M.9 and P 22 and new rootstocks P 61 and P 62 produced no significant effect on the size, weight and colouring of apples, with the exception of 'Jonagold' and 'Gala' trees growing on P 59. In 2004, the apples on this rootstock were significantly smaller.