Effect of new Polish clonal rootstocks on growth, yield and fruit quality of two apple cultivars

Polish rootstocks from the new P series were tested for 'King Jonagold' and 'Redkroft' apple cultivars. The field experiment was established in the autumn of 1996 at., the Experimental Orchard in Dqbrowice, near Skierniewice (Central Poland) on a sandy loam podsolic soil underlaid by loam. The influence of dwarfing and semi-dwarfing rootstocks, as well as subclones of M.9, on the growth, yield and fruit quality of two apple cultivars was studied. In 1996-2003, results showed that the new Polish rootstocks: P61, P63, P64, P65 and the Byelorussian PB-4 decreased tree growth of both cultivars. Sizes of these trees were significantly smaller, compared to P22 (the control). Growth of trees grafted on German subclones of M.9 (B.1, B.2 and B.3), was similar to those of trees on M.9 EMLA (standard). The new Polish very dwarfing rootstock selection, P62, significantly decreased tree growth of 'King Jonagold' cv., compared to the M.9 EMLA control. Among the semi-dwarf rootstocks tested, P67 reduced tree growth to the same degree as M.26 (standard). For the cultivar 'King Jonagold', P66 appeared to be a more dwarfing rootstock than M.26. However, for 'Redkroft', both Polish rootstocks (P66, P67) decreased tree growth significantly. The highest cumulative yield of 'King Jonagold' was obtained from trees grafted on M.9 B.2., but in the case of 'Redkroft', from trees on semi-dwarfing rootstocks: P67 and M.26. Tree productivity results, expressed as the yield efficiency index, showed that 'King Jonagold' trees on all rootstocks were more productive than those of 'Redkroft'. The highest yield efficiency index achieved with 'King Jonagold' was obtained from trees grafted on P63. In 2003, fruit quality parameters (size, weight and share of fruits with blush over more than 50% of skin) of both cultivars were very good. Significant differences were obtained only in the colouring of fruits harvested from trees of 'King Jonagold' grafted on very-dwarfing rootstocks. In this case, fruits from trees on P63 were the worst Coloured.