MILDEW (Podosphaera leucotricha ELL. ET EV./SALM.) SUSCEPTIBILITY IN APPLE PROGENIES WITH SEGREGATION FOR SCAB RESISTANCE

Apple breeding in the Czech Republic over the last 25 years has been mainly aimed at scab resistance. Progenies of cultivars or other donors carrying Vf consist of about 40% of scab resistant seedlings but the majority of them are susceptible to mildew. With an objective to study relation between scab and mildew segregation more thoroughly a progeny (´Golden Delicious´ x ‘Purdue R7T41’) of 750 seedlings was completely quantitatively evaluated using 1-9 rating scales for 8 years regarding incidence both of scab and mildew under conditions of the natural spread of the diseases. Finally, 25,3 % seedlings were rated as scab resistant (score 9), whereas in the case of mildew only 5,5% and 0,8% ones respectively were rated by scores 7 and 8 which correspond with some levels of mildew tolerance. Correlation coefficient of r = -0.17 was calculated with both data sets. Regarding mildew, in some progenies of ´Priam´, ´Prima´, ´Florina´ and ´Liberty´ on average 27% of the seedlings were rated as highly susceptible, 57% as susceptible and only 16% as moderately susceptible. No one from them was classified as less susceptible. On the other hand several progenies were found in which segregation of mildew tolerance of an average level of 10% appeared. This desirable level of reduced susceptibility to mildew originates from ´Antonovka´, ´Discovery´, ´Lord Lambourne´ ´Redspur Delicious´, ´Spätblühender Taffetapfel´, and some other varieties.