Purpose. To analyze the divergence of early maturing source material of corn Zea mays L. in heterosis breeding for the genetic base formation at the State Institution the Institute of Grain Crops of the NAAS of Ukraine. Methods. Field (comprehensive assessment of morphobiological and economically valuable characteristics of the source material and maize hybrids) individual selection, cumulative and recurrent selection, backross and testcrosses bree­ding methods; laboratory; analysis and synthesis; statistical. Results. The results of research on the analysis of the divergence of early maturing corn source material in the conditions of the Steppe of Ukraine has become a developed harmonized working collection of corn breeding samples adapted to the stressful conditions of this region. The gradual cyclical improvement of the lines made it possible to form the core of the genetic diversity of FAO 150–290 early maturing specimens of the southern ecotype, which are competitive in heterosis breeding. The complexity of breeding for early maturity in the steppe conditions is due to the lack of material adapted to the stress factors of the South of Ukraine. The available early maturing lines of the world collection F2, F7, Ер1, Ма21, Ма23, Со125, Со255, См7, PLS61, S72, etc., were distinguished by high cold resistance, good starting plant development, intensive accumulation of dry matter during ripening, but not adapted to the deficiency of moisture in the soil and high summer temperatures. According to the results of the experiment, it was revealed that, in terms of breeding, lines of Lancaster plasma (DK427 and DK633) were the most plastic, due to which a number of new mid-early lines were obtained, for example DK2/427, DK267, DK266/417, DK633/266, DK296, etc., which were included in the registered hybrids. Formation of the genetic base of early maturing maize source material for heterosis breeding and systematization accor­ding to different breeding characteristics provided a balance of samples of alternative components, which will be further used to model heterosis hybrids in the early maturing group. Conclusions. The updated basic collection of lines is represented by the samples of plasma Iodent: DK744SVZM, DK216SVZM, DK4173SVZM, DK235zS, DK257zM, SV, DK365SVZM, DK777ZMSV, DK733-7zM,SV, DK315SVZM; Lancaster: DK296zS,VM, DK633/266zS,VM, DK2965ZSZM, DK2953 ZSZM, DK3023 ZSZM, DK236zS,ZM; Raid (SSS): DK232MV, DK2323MV, DK239MV; Mixed: DK253ZSZM, DK273MV, DK272zS, DK281SV, DK233zM,SV, DK959MV, DK9527 ZSZM, DK247MV, DK2442MV, which is the basis of the genetic diversity of early ripening corn samples included in the State register of plant varie­ties suitable for dissemination in Ukraine.

Assessment of agroclimatic conditions in 2012–2014 and their effect on formation of frost resistance and winter hardiness of soft winter wheat is made. Elevated temperature conditions in autumn and disturbance of cold hardening conditions caused the formation of the highest frost tolerance and winter hardiness of winter wheat only up to -15°C. Under the new climatic conditions the modern varieties of myronivska breeding are able to realize 80–85% of the genetic potential by the property.

For the resistance to a soil drought in the early stages of seed germination the key role plays the primary root system: an activity of seed germination, the number of seminal roots and their length, dry weight of roots and coleoptile length and also the degree of cold resistance at the seedling stage. The stages and methods of the creation of six-row medium-grown barley varieties Vakula and Helios and semi-dwarf varieties Ros and Halychanyn are described.