Adaptation of high-yielding winter wheat crops to changes in climatic conditions has great importance for food security of countries. The remobilization of stem assimilates for grain filling is one of the possible ways of increasing wheat yield in unfavourable environmental conditions. Field experiments in natural conditions with three old and three modern varieties of winter wheat were performed to compare depositing abilities of their stems. The objective of this study was a comparative analysis of the parameters of depositing capacity of stems of the main shoots for identification of the criteria for assessing grain productivity of winter wheat. The parameters of depositing capacity of the stem of the main shoots of three old winter wheat varieties (1997, 2003, and 2008) and three modern ones (2013, 2014 and 2016) were studied in field conditions with natural conditions of water supply (Kyiv Oblast, Ukraine). During the period of formation of reproductive organs (April and May), the amount of precipitation, respectively, was only 17% and 68% of long-term values and average monthly air temperature was 3–4 ºС higher than the climatic norm. We analyzed the variability of the parameters of depositing capacity of the stem of the main shoot and grain productivity of the ear of six wheat winter varieties which differed by time of selection. In unfavourable conditions during the period of formation of reproductive organs the modern winter wheat varieties had an 11% higher yield on average compared to the older ones. It was determined that the highest mass of grain from the ear of the main shoots (1.9–2.1 g) belonged to Odeska 267 variety, a drought-tolerant variety from earlier selection, and three modern varieties – Raihorodka, Prydniprovska and Darunok Podillia. It is demonstrated that these varieties also exceeded two old varieties (Podolianka and Yednist) by stem dry matter weight of main shoot at anthesis by 0.3–0.6 g. The highest content of non-structural carbohydrates at this phase was observed in Odeska 267, Raihorodka and Darunok Podillia varieties (273–307 mg/stem). Correlation analysis revealed the significant correlation between mass of grain from ear and dry matter of stem at anthesis and full ripeness, as well mass of grain from ear and the amount of non-structural carbohydrates at anthesis. Therefore, modern varieties of winter wheat and the drought-tolerant variety have higher yield, weight of dry matter of stem of the main shoot at anthesis and grain productivity of the ear, compared to old varieties. The results of this study indicate that the mass of dry matter of the stem of the main shoot at anthesis can be used as a marker of the grain productivity of winter wheat.

Aim. Analysis of physiological and biochemical characteristics and grain productivity traits of transgenic common wheat plants (Triticum aestivum L.) with a double-stranded RNA suppressor of the proline dehydrogenase gene (pdh) compared to non-transgenic genotypes under conditions of soil drought. Methods. Biochemical assays: spectrophotometric measurements of antioxidant enzymes (SOD, APX) activity, proline dehydrogenase activity and free L-proline content; biotechnological assays: Agrobacterium-mediated transformation in planta; physiological: morphometric traits and elements of grain productivity; mathematical statistics. Results. The presence of a double-stranded RNA suppressor of the gene pdh in transgenic plants leads not only to a decrease in enzyme activity (on average 2 times compared to the nontransgenic plants), but also to an increase in the content of free L-proline both under optimal conditions and under soil drought (2.6–4.1 times). Under soil moisture defi ciency, transgenic plants with reduced pdh gene activity in terms of yield structure signifi cantly exceeded the corresponding values of grain productivity elements for the non-transformed ones. In terms of the grain weight from the main stem, the biotechnological plants under soil moisture defi ciency exceeded the control plants 1.5–1.6 times, while the number of grains did not differ signifi cantly. The grain productivity of the whole plant in the transformed lines under conditions of soil moisture defi ciency was somewhat inferior to those in the nontransformed plants grown under optimal conditions. Soil drought caused a signifi cant increase in SOD and APX activity (by 40 and 11 %, respectively) in plants of the original variety. On the contrary, the activity of both antioxidant enzymes under drought conditions in transgenic plants decreased: SOD – down to 73–76 %, APX – down to 82–86 %, compared with the variant of 70 % of fi eld capacity. Conclusions. The analysis of physiological and biochemical characteristics, as well as economic and grain productivity elements of transgenic common wheat plants with a double-stranded RNA suppressor of the proline dehydrogenase gene showed their increased tolerance to soil drought, compared with non-transgenic genotypes, which may be associated with higher proline accumulation and an increase in the antioxidant enzymes activity. Under soil moisture defi ciency, transgenic wheat plants with reduced pdh gene activity signifi cantly exceeded the corresponding values of grain productivity elements for non-transformed plants. The analysis of the antioxidant enzymes activity in the chloroplasts of transgenic plants showed that under physiological conditions, the antioxidant system works more actively in comparison with non-transgenic genotypes, which may be a prerequisite for increasing the tolerance of these plants to the infl uence of stressors of various origin. It is likely that the positive relationship between the level of free L-proline and the resistance of transgenic wheat plants to osmotic stress is associated either with the effect of L-proline on the expression of other genes of the stress-strain response of plants, or with the positive effect of the increased content of this amino acid on resistance at the early stages of stress development. It has been suggested that an increase in the antioxidant enzymes activity in biotechnological plants can be caused by the expression of heterologous genes.

Aim. A comparative analysis of several traits of the capacity of the assimilation apparatus of 10 varieties and 2 lines of winter wheat from Ukraine, under conditions of insuffi cient precipitation and elevated air temperature during the period, when the reproductive organs formed (GS 30–49), in order to search for phenotypic markers associated with high productivity. Methods. Field, morphometric, spectrophotometric and statistical methods were used. Results. The maximum difference in yield between varieties and lines, which grew under condi- tions of insuffi cient water supply and high temperatures in April and May of growing season 2017/2018, was 24.7 %. Under these conditions, the highest grain productivity was observed for the new varieties Pochayna, Hospodarka and Kyivska 17 (8.60–8.73 t/ha) and a high canopy leaves chlorophyll index at late stages of ontogenesis (0.38-0.48 g chlorophyll/m 2 at milky-wax ripeness). This was opposed to varieties Smuhlianka, Poradnytsia and the line UK 392/15 with the lowest yield (7.00–7.25 t/ha) and assimilation surface at this stage (0.07–0.17 g chlorophyll/m 2 ). At the fl owering stage (anthesis) the most productive varieties exceeded the least productive ones, on average, by 30 % in leaves fresh weight of the canopy, by 24 % in content of total (a+b) chlorophyll and by 60 % in canopy chlorophyll index. At milky-wax ripeness, the differences between these varieties increased signifi cantly – up to 136 % in leaf fresh weight of canopy, 57 % in chlorophyll content and 350 % in canopy leaves chlorophyll index. A close positive correlation (r = 0.69–0.77, P ˂ 0.01) between the canopy photosynthetic apparatus traits at milky-wax ripeness with the yield of varieties and lines of winter wheat under drought and high temperature stress was found. Conclusions. The results show that the leaves fresh weight of canopy and canopy leaves chlorophyll index can be used as markers of grain productivity of winter wheat under drought stress, as well as for the possible development of molecular genetic criteria of breeding, based on these phenotypic characteristics.

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Aim. Comparative analysis of the traits of the assimilation surface of winter wheat varieties under unfavorable environmental conditions to evaluate its adaptive capacity. Methods. Morphometric, spectrophotometric, statistical. Results. In the field experiments under natural conditions (close to optimal in spring, arid - during the grain filling period and prolonged rainfall during a harvest), the variability of leaves chlorophyll content, the green leaves fresh matter per 1 m2 of ground and chlorophyll index in 10 modern middle-early varieties at anthesis and milky-wax ripeness were studied. Under such conditions, the difference in grain productivity between the highest and the lowest yielding varieties was about 1.6 t/ha. Positive correlation of grain productivity of winter wheat varieties with chlorophyll area index of leaves at milky-wax ripeness (r = 0.61) was established. Conclusions. It was found that the varieties with better adaptation to drought conditions during the period of grain filling had a higher area of assimilation surface at anthesis and milky-wax ripeness. Therefore, their higher yield was related to the higher photosynthetic capacity and the ability to storage and remobilization of carbohydrates deposited in the stem as well as to the efficiency of converting total biomass into grain yield (HI). Keywords: Triticum aestivum L., grain productivity, chlorophyll area index of leaves.