BREEDING OF ROOTSTOCKS WITH HETEROSIS EFFECT SUITABLE FOR GERMAN PRUNE AND FUNDAMENTAL PLUM VARIETIES IN CZECHOSLOVAKIA

The culture of plums is very important in Czechoslovakia (Vávra, 1963). There are over 15 millions plums, i.e. 31% of all fruit trees; more than 80% trees of this number make German Prune; gages, yellow plums and Durancie, 20%. One and half century ago the plums took 2/3 of the whole number of fruit trees. They were grown in country orchards, along the roads and ditches. German Prune and Durancie were propagated by rootshoots separated from parent plants. These were hardfrost with fruits of high quality. From these trees Brnenská Plum of high quality was obtained (Vávra, 1965 a). Fruits of this plum were eaten raw and cooked in cakes, stewed, dried, prepared as' james and plum-brandy. Fruits of Durancie were prepared as james and plum-brandy. These have been and are still now the article of foreign trade.

In the half of last century field orchards were planted with German Prune. As planting material were used trees on their own roots and rootshoots of Durancie, which were grafted with German Prunes in the nursery already. For a lack of these materials, sowing of German Prune stones began. Their germination was bad and their growth was weak. Intergrafting was introduced in that way, that the plum seedling was grafted with one of the vigorous plum varieties in the root neck (Belle de Louvain, The Czar, Count Althann's Gage or Tragedy), but in the crown with German Prune or some else noble plum variety.

As there was a great demand after German Prune trees, the nurserymen examined other rootstocks as seedlings, St. Julien (from France), Durancie and Myrobolan-Cherry Plum (from France, Italy, Bulgaria). The best results were obtained by propagating plum varieties on Myrobolan. From the beginning