PERFORMANCE OF TWO APPLE CULTIVARS ON P SERIES DWARF ROOTSTOCKS
The crosses were made in the years 1954 to 1956. Following preliminary screening 9 clones were selected and tried in test orchards. The tested rootstocks were budded with 2 apple cultivars, McIntosh and Starking Delicious, and were compared with 6 standard rootstocks giving a range of vigour control. In a separate trial winter hardiness of the P rootstocks was assessed under field conditions. In addition their rooting ability and propagation index were compared with those of the known rootstocks.
Four of the P clones, P 1, P 2, P 16 and P 22 proved dwarfing. Of these P 1 and P 16 propagated and rooted better than M.9 while P 2 and P 22 were similar to M.9 in these respects. The level of winter hardiness of P 1 and P 16 was similar to that of M.9 while P 2 and P 22 were considerably more winter-hardy. In that respect they were equal to A 2 or Antonovka seedlings. The level of resistance of the P rootstocks to collar rot was apparently similar to that of M.9.
All the above listed P rootstocks induced very precocious bearing and high productivity in trees worked on them. As the rootstocks are still in short supply the clones P 2 and P 22 are extensively used in the Polish apple industry as dwarfing interstocks.