The Influence of Different Rootstocks on the Growth and Yield of Sweet Cherry Trees during the First Four Years after Planting in the Double Row System

'Regina', 'Sylvia', 'Lapins' and 'Summit' sweet cherry (Prunus avium L.) trees grafted on 'GiSelA 5' (P. cerasus 'Schattenmorelle' x P. canescens), 'P-HL A' (P. avium x P. cerasus) and 'P-HL B' (P. avium x A cerasus) dwarfing rootstocks were compared with trees of the same cultivars on the vigorous rootstock IF 12/1' (P. avium) (control). The trees were planted in the double row growing system at distances of 4.5 x 2.5 + 1.5 m (1360 trees/ha). The data collected included tree vigour, yield and fruit weight, as well as the number of buds on each tree in the second year after planting. The results revealed that the rootstocks 'GiSelA 5', 'P-HL A' and 'P-HL B', in comparison to IF 12/1', significantly reduced the growth of sweet cherry trees. Depending on the cultivar, trunk cross-sectional areas of four-year-old trees grafted on 'GiSelA 5' were from 22% ('Lapins') to 59% ('Sylvia') smaller than those on IF 12/1'. Tree growth was depressed between 43 and 49% on 'P-HL A' and from 21 to 28% on 'P-HL B'. 'Lapins' trees, regardless of the rootstock, tended to produce branches with narrow crotch angles. No suckers under the trees were found so far. All sweet cherry trees grafted on 'GiSelA 5', 'P-HL A' and 'P-HL B' had a higher number of flowers than the control trees, indicating that these are precocious and very early-bearing rootstocks. Cumulative yields for all of the sweet cherry trees on the dwarfing rootstocks were higher than for the control trees. Already in this preliminary period, the productivity of the dwarf trees was several times higher than that of the trees on IF 12/1'. The rootstocks influenced fruit weight significantly. However, in the case of each cultivar, the results were a little different. Generally, 'P-HL B' and 'GiSelA 5' had the best effect on fruit size.