THE EFFECT OF INTERSTOCKS OF M.9 AND B.9 ON THE FIELD PERFORMANCE OF THREE APPLE CULTIVARS

Dwarf apple trees are the most suitable for modern intensive orchards but trees on M.9, which is the most widely used dwarfing rootstock in Western Europe, have their roots damaged by winter frost under Polish conditions. The use of dwarfing interstocks on hardy (Antonovka) rootstocks were therefore tested as an alternative approach to obtaining dwarf trees for Polish conditions.

There were some differences in the effectiveness of the interstocks in growth control depending on scion variety but in general trees with M.9 or B.9 rootstocks or interstocks were 48–83% smaller than trees grafted directly on Antonovka seedlings. In some cases the interstock trees were even smaller than those on M.9 or B.9 rootstocks. Productivity was higher when M.9 or B.9 was used as either rootstock or interstock than when seedlings alone were used.

The interstock trees were much more liable to produce root suckers than trees on M.9 or B.9 rootstocks. During the 14 years of the trial about 40% of the trees on M.9 and B.9 rootstocks were lost, mainly because of poor anchorage, while only 12% of the M.9 and B.9 interstock trees were lost, mainly by mouse damage. Trees with B.9 interstock are therefore recommended for Polish conditions.