Results of experimental research work which allowed to establish advantages of in-terspecsfic hybrids over intervarietal ones as to their resistance to ditylenchosis were presented; the advantages were proved by the possibility to isolate among the former forms with extremely high resistance (9 points), considerably greater (2,3 - 6,4 times) number of hybrids which exceed index of the character in the best variety-standard. Backcrosses 81.459c19, 82.203c79, 90.690/61, which are unique having shown no symptoms of disease during the 3 years of testing. Higher value of interspecsfic hybrids as compared with intervarietal ones as to their resistance to common scab of potato lies in higher (2,8 times) frequency of high resistant forms and in lower (2,9 times) number of considerably affected materials, in greater number of hybrids with higher resistance, than in the best variety-standards; only interspecsfic hybrids without disease symptoms were defected (27,9; 3,3; 21,3%). Effective genetic control of the character is inherent in separate backcrosses (81.459c15, 83.47c65). It is only among interspecsfic hybrids that the forms with higher resistance to ring rot as compared with the best variety-standard were found. Parent components of crosses which have repetition among resistant material were isolated, namely Granat, 80.24c6, 91.1686/2, 81.386c65. The advantage of interspecsfic hybrids over intervarietal ones in resistance of tu-bers to late blight is shown by the absence in the former of the forms very susceptible to the disease, by the presence of backcrosses with high and even extremely high resis-tance. This applies equally to the to the resistance to iron spots of tubers. Intervarietal, interspecsfic hybrids with high resistance to the four above-mentioned diseases were isolated (2 pieces for each). Seven intervarietal hybrids are superior to the best variety-standard in yields and other characters. Multituber character and high starch content are typical of the interspecsfic hybrids. The influence on thepenetration of Phytophthora into tubers of the features of fe-male forms (backcrosses), pollinators (varieties) and their interaction is proved. Effi-cient genetic control of the character is typical of the five species hybrid 90.841c2, and among varieties of Poliska rozheva. The same is true about the fungus spreading. The author participated in the development of five varieties, the four of which are recommended for growing in all zones of Ukraine: these are Vesta, Dara, Tyras, Malin-ska bila. Their growing is very retable.
