Response of sunflower hybrids of different maturity groups to the temperature regimen during vegetative period

Sunflower hybrids of different maturity groups were tested at the Plant Production Institute nd. a. V.Ya. Yuriev of NAAS (Kharkov) in 1998-2015 by the method of competitive variety trials. The institute's breeding hybrids that were the best by the complex of traits were used as the material for the investigation. The purpose of the research was to evaluate the relation of hybrids yield from the temperature regimen during vegetative period. Correlations between yield, temperature in the germination - flowering period and its duration were established. The average maximum daily temperature of the vegetative period had the greatest effect on yield. In total over the research years, hybrids with the duration of the germination - flowering period 60 days had the advantage on yield. The hybrids with the duration of the germination - flowering period 57 and 65 days had the lower yield. Basing on the flowering date, we identified the maturity groups of hybrids that were beneficial on yield in years with relatively low or high temperatures during the vegetative period. Hybrids with the duration of the germination - flowering period 57 days had the advantage on yield in years with relatively low heat supply of the vegetative period. Increase of the average maximum daily temperature in June on 2 °C (to 29 °C) caused a decrease in the yield of hybrids belonging to different maturity groups on 0.07-0.97 t per ha. Increase of the average maximum daily temperature in August (to 33 °C) caused an increase of yield in all maturity groups on 0.23-0.38 t per ha. The yield of sunflower hybrids belonging to the different maturity groups associates with the temperature regimen during the vegetative period especially.