GENETICAL IMPROVEMENT OF PLUMS IN CZECHOSLOVAKIA

The traditional plum assortment grown in Czechoslovakia involved mostly clones of ‘Domestic plum’. After the plum pox spreading in the Sixties ‘Reine Claude’ group was preferred and in the last 10 years also some cultivars tolerant to Plum Pox Virus (PPV), mainly ‘Stanley’ and ‘Cacanska najbolja’. From the cultivars bred here in the past some 5 are still important and they are also recommended as parents for further breeding. In the present breeding programs developed since the Fifties 5 plum rootstocks were bred, the most perspective of them the P. myrobalana clone MY-KL-A and the vegetative plum rootstock S-BUPR-A. All the source material of cultivars and rootstocks is already virus-free. In breeding new cultivars 3 advanced selections were obtained, which are tested in the State Varietal Trials. In the frame of the wide collection investigations 260 cultivars were tested, 8 of them are now recommended for growing and others for further breeding. Now the evaluations are oriented on PPV tolerance and on the resistance to some other diseases and pests.

For many decades the plum assortment in Czechoslovakia was established mostly on local clones of ‘Domestic Prune’. For a very long time the cultivar participated with 70 % on the whole number of trees. A certain variation about the share was caused by frosts injuring periodically fruit tres in Czechoslovakia in 10 to 15 years' intervals. About 15 % were less valuable local plum types (mostly from the ‘Damson’ and Myrobalana groups) and the rest of other cultivars, mainly ‘Reine Claude verté’, ‘Wangenheim’, ‘Althans Reine Claude’ and many others (Nemec, 1955; Vávra et al., 1963).

Substantional changes began in this assortment after the common spreading of the Plum Pox Virus (PPV). Since that time, ‘Domestic Prune’