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Heat stress during the grain-filling period has a substantial effect on embryo development, and on the size and chemical composition of the grain. The lines of a doubled haploid population arising from a cross between a heat-sensitive (Plainsman V) and a heat-tolerant (Mv Magma) wheat variety were analysed to determine how these changes influenced the germination of kernels formed during heat stress and the initial development of the seedlings. Heat stress during the early grain development of the main spike had a significant influence on the yield components, which differed however for the main and side spikes. Considerable differences were observed in the extent to which the yield components declined in the individual lines. Averaged over the population, the germination percentage, and the shoot and root length and root number of the seedlings did not differ significantly for seed originating from heat-stressed and control plants.

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Authors: K. Balla, I. Karsai, S. Bencze, T. Kiss and O. Veisz

Stress tolerance is associated with the activation of antioxidant compounds and enzyme systems that are capable of neutralising the reactive oxygen species (ROS) continually produced in response to stress. The present experiment was designed to compare the heat tolerance of four winter wheat varieties in the shooting and grain-filling stages by investigating changes detected in antioxidant enzyme activity and yield components in response to heat stress.Heat treatment was found to cause a significant rise in the activity of the glutathione-S-transferase and catalase enzymes, while there was usually a less intense decline in the activity of guaiacol peroxidase.An analysis of yield data revealed that heat stress had a more pronounced effect during grain filling in this experiment than at the beginning of shooting, as shown by the greater reduction in thousand-kernel weight and yield.

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Phytotron experiments were conducted to examine the impact of elevated atmospheric CO2 level (750 μmol mol−1) on the drought tolerance of winter barley (Petra), durum wheat (Mv Makaroni) and spring oat (Mv Pehely) varieties. Under drought stress conditions, the durum wheat variety was found to be unaffected by CO2 enrichment, as neither the biomass or grain yield nor the antioxidant enzyme activities changed compared to those at ambient CO2. Despite the fact that the spring oat variety had similar grain yield loss due to drought at both CO2 levels, it exhibited reduced antioxidant enzyme activities under less severe drought, indicating a slightly increased tolerance to drought. Winter barley, which exhibited an extremely positive reaction to CO2 enrichment at the control water supply level, also showed increased drought tolerance in response to high CO2. It had low glutathione reductase, glutathione-S-transferase and ascorbate peroxidase activities even at the most severe drought stress levels, while it could also fully compensate for the negative effects of drought on biomass and grain yield parameters when grown at elevated CO2.

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The impacts of climate modification were examined in terms of changes in the stress tolerance of winter wheat varieties. The enzyme reactions of two winter wheat varieties to drought stress, simulated by water withholding in three different phenophases, were analysed in a phytotron experiment in the Centre for Agricultural Research, Hungarian Academy of Sciences. Plants were raised either at ambient CO2 level or at twice this concentration. The quantities of glutathione reductase (GR), glutathione-S-transferase (GST), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) were determined from leaf samples collected at the end of the drought treatment.The results showed that antioxidant enzymes may help to counterbalance the reactive oxygen species induced by stress during various stages of the vegetation period. Although there were substantial differences in the changes induced in the activity of individual enzymes by modifications in environmental factors, this activity and its response to stress depended not only on these factors, but also on the developmental stage of the plant. Modifications in enzyme activity could indicate that enhanced CO2 concentration delayed the development of drought stress up to first node appearance, and stimulated antioxidant enzyme activity when drought occurred during ripening.

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Over the last two centuries the atmospheric CO2 level has exhibited a consistent rise, leading to an increase in the greenhouse effect. This level is now 35% higher than it was before the industrial revolution. On the basis of various scenarios from the Special Report on Emissions it is expected to rise from the present level of 385 ppm to 650–970 ppm by the end of the 21st century.Plant biomass and resistance of winter wheat to various powdery mildew pathotypes were investigated at normal (400 ppm) and enhanced (700 ppm) atmospheric CO2 levels in a greenhouse. Wheat cultivars Ukrainka and Mv Hombár, and 12 lines from the mapping population developed from their cross and exhibiting different level of resistance were tested.The results showed that the atmospheric CO2 level had little influence on the resistance of winter wheat to powdery mildew infections based on the percentage of leaf area covered whole plant percentage severity. In response to higher atmospheric CO2 level there was an increase in the aboveground biomass of the winter wheat genotypes tested in the present work, leading to an increase in plant height and in stem and leaf weight. However, the number of tillers and the grain yield did not increase compared with the values recorded at normal atmospheric CO2 level.

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Authors: K. Balla, S. Bencze, T. Janda and O. Veisz

As a consequence of climate change, the incidence of extreme weather events has increased in Hungary, as elsewhere. Extremely high temperatures are the factor causing the greatest problems for agriculture and crop production. The aim was to determine the heat tolerance of two wheat varieties (Plainsman V. and Mv Magma) by measuring physiological and yield parameters under high temperature conditions (35/20°C day/night) in the phytotron. Heat stress had a substantial influence on the chlorophyll content, antioxidant enzyme activity and yield parameters of the two winter wheat varieties. Heat stress during grain filling led to a significant reduction in the yield, biomass, grain number, harvest index and thousand-kernel weight. Significant differences could be detected between the two varieties, confirming the greater heat sensitivity of Plainsman V. and the better heat tolerance of Mv Magma. The importance of the antioxidant enzyme system was demonstrated in defence against heat stress. The activity of the enzymes glutathione-Stransferase (GSH-S-Tr), ascorbate peroxidase (APx) and catalase (CAT) was enhanced in Plainsman V., and that of GSH-S-Tr and CAT in Mv Magma. The tolerance of the wheat varieties appeared to be correlated with the antioxidant level, though changes in activity were observed for different antioxidant enzymes in the two genotypes tested.

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A long-term experiment was started in 2005 in the Agricultural Research Institute to monitor the effects of extreme climatic events on the grain yield, quality and disease resistance of cereals. The yield was poor in 2007 due to the long dry period from autumn till spring, while it was high in 2006 and 2008 when there was more precipitation. The grain quality was the highest in 2007, however, despite the extreme weather events. Fungicide treatment generally resulted in higher yield potential and better grain quality in every year.

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The unfavourable effects of climate change were studied in terms of changes in the stress tolerance of cereals. The yield and physiological parameters of two winter wheat genotypes (Mv Mambó, Mv Regiment) were analysed in the phytotron after water was completely withheld for 7 or 14 days in three phenophases. The plants were raised in climate chambers, one adjusted to ambient CO2 concentration and the other to a higher level (750 μmol mol−1). The aim of the present work was to determine the correlations between the duration of water withholding and the phenological, physiological and yield parameters of winter wheat. It was hoped to identify how elevated CO2 levels affected the stress sensitivity of plants and whether they contributed to counteracting the damaging effects of drought. In both varieties, the grain mass decreased to the greatest extent when water was withheld at first node appearance (5.9–71.3%). A longer period of drought at first node appearance and grain filling only reduced the grain number and mass in the case of enhanced CO2. The yield and physiological parameters of Mv Regiment, however, deteriorated substantially as a result of water deficiency, though this variety was better able to utilise surplus CO2, giving outstanding results at elevated CO2 level.

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Finding and improving wheat cultivars with good adaptability to abiotic stress is an important objective in breeding programmes. An experiment was set up in the climate chamber of the Martonvásár phytotron to test the effect of heat and drought stress on two winter wheat varieties and one variety of durum. Wheat plants exposed to 35°C and drought during grain filling exhibited altered agronomic and grain quality characteristics. Drought was found to have a much greater influence on yield and quality than heat stress. Reductions in the unextractable polymeric protein fraction and the glutenin-to-gliadin ratio indicated poorer grain yield quality as a result of drought, despite higher protein content. Quality deterioration was observed after drought, while heat stress had no noticeable influence on the protein quality of the three wheat genotypes, measured using size exclusion high performance liquid chromatography (SE-HPLC). The durum variety had a better ratio of protein components and a significantly higher Zeleny value when exposed to heat stress, although it had the lowest grain yield and grain/straw ratio.The most significant negative correlation was observed between the Zeleny value and the unextractable polymeric protein (UPP%) fraction after heat treatment and between the relative protein content and the albumin+globulin % (AG%) in the case of drought. These correlations testify that these parameters play an important role in determining the baking quality of wheat flour.

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Authors: S. Bencze, I. Keresztényi, B. Varga, B. Kőszegi, K. Balla, A. Gémesné-Juhász and O. Veisz

The effect of CO2 enrichment on the rate of photosynthesis and the water use efficiency (WUE) of young pepper and tomato plants was studied in the phytotron. A CO2 level of 1000 ppm significantly increased the net assimilation rate in the upper foliage, while the increase was even more considerable in the lower layers of the canopy, with values of up to 100%. The 1500 ppm CO2 level caused a further substantial increase in CO2 assimilation and at least doubled (in tomato) or tripled (in pepper) the water use efficiency on a leaf area basis compared to the ambient values. Although the response in terms of photosynthesis and WUE was not variety-specific, there were differences between the pepper hybrids in the biomass components, exceeding 100% for the total biomass at the 1500 ppm CO2 level. In tomato, however, there was no significant variation in the total biomass of the three hybrids investigated in this early phase of development at either CO2 level.

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