Winter hardiness of bulgarian winter wheat variety samples under conditions of Forest-Steppe of Ukraine

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Purpose. To study winter wheat samples bred in Bulgaria for the trait "winter hardiness" followed in further use as starting material for breeding. Methods. Field studies, experimental freezing, mathematical and statistical. Results. A comprehensive evaluation of 1470 samples has been carried out for the period 1987–2013 on the experimental fields at the Myronivka Institute of Wheat and the best winter hardy and frost resistant samples have been defined. In the 27 years of research, adverse weather conditions during winter periods were marked in 32 per cent of the cases thus resulted in partial or total death of the material and made it possible to objectively estimate the level of winter hardiness and frost resistance of the Bulgarian samples. By direct freezing in low temperature chambers KNT-1 there were determined the level of frost resistance of 40 samples with four of which being at the standard level for this trait (102-72, 2579-30-19, 1769-64 and 148-133-21). The level of overwintering was characterized with wide variation (R = 82.9 %, in standard 53.8 %). There were identified the variety samples with high resistance (7-8 points) to the yellowing of leaf surface after overwintering, increased tiller number and regenerative capacity in combination with rapid pace of spring regrowth, as well as high level of winter hardiness which was confirmed in years with extreme conditions of overwintering. A reliable positive correlation of moderate strength (r = 0.44, p <0.05) was found between winter hardiness (score of overwintering) and yield as well as weak correlation between winter hardiness and plant height and resistance to Septoria leaf blotch (r = 0.12 and r = 0.21, respectively) was revealed. No relationship was found between winter hardiness and brown rust affection and resistance to powdery mildew (r = 0.02 and r = -0.08, respectively) thus indicating the possibility of combining these traits in one genotype. Conclusions. The Bulgarian variety samples M–1022–6567, 6687–12 combining high winter hardiness with yield, short stem, early ripening, disease resistance and high kernel weight as well as 2579–30–19 combining high winter hardiness with yield, frost resistance, short stem, disease resistance, high kernel weight and grain quality are of the greatest interest for breeders. When involving the last sample, new high-yielding variety Hospodynia myronivska has been developed.