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Among the abiotic stress factors influencing the growth and productivity of wheat varieties, extremely high temperatures have the most limiting effect. In an experiment set up in the gradient chamber of the Martonvásár phytotron to test the effect of various temperatures on four winter wheat varieties and one variety of spelt, substantial differences were observed in the heat stress tolerance of the varieties. There was a considerable reduction in the number of shoots and spikes as the result of heat stress, leading to a drastic loss of grain yield. It was clear from changes in the biomass and in the grain:straw ratio that extremely high temperatures led to a substantial reduction in the ratio of grain to straw in the varieties tested. In response to high temperature the wheat plants turned yellow earlier due to the rapid decomposition of the chlorophyll content. This resulted in a considerable shortening of the vegetation period and early ripening. Reductions in the parameters tested were observed at different temperature levels for each variety, indicating considerable differences in the ability of the varieties to adapt to abiotic stress factors.
Numerous Fusarium species have been associated with the Fusarium head blight (FHB) disease of wheat, barley and other small-grain cereals, reducing worldwide cereal crop yields and, as a consequence of their mycotoxin production in the cereal grain, having an impact on both human and animal health.The year 2010 was extremely favourable for Fusarium head blight pathogens. Over a hundred symptomatic wheat heads were collected from various locations in Hungary. The aim was to determine the diversity of the Fusarium species infecting winter wheat ears. A total of 86 Fusarium spp. were morphologically identified from diseased kernels. F. sambucinum was found to be present in two of the Martonvásár samples. This pathogen had only previously been detected extremely sporadically. The species F. culmorum and F. verticillioides were found at a much lower rate than expected, while none of the isolates were identified as F. poae. On the basis of the results, 95% of the isolates belonged to the Fusarium graminearum species complex.
One basic precondition for the reliable cultivation of winter durum wheat (Triticum durum Desf.) in Hungary is for the varieties to have good winter hardiness and frost resistance. Field overwintering experiments carried out in Martonvásár between 1995 and 2003 demonstrated that there was a significant difference every year between the overwintering of varieties with poor and good frost resistance, though only in two years was there a significant difference between that of varieties with medium and better frost resistance. Only a medium correlation was observed between the mean annual values of the air temperature in the winter months and the winter hardiness of the varieties, confirming that winter hardiness is influenced jointly by a number of environmental factors (e.g. cold, snow cover). In the experiments carried out on the winter hardiness dynamics of durum wheat, it was found that in milder winters even T. durum varieties which are sensitive to frost overwintered with little damage, while in the two coldest winters during the experimental period the hardiness of these varieties did not provide sufficient protection even in December, and all the plants were destroyed by January. The early spring frosts experienced in 1996 proved in these experiments that spring frosts may cause considerable damage even to durum wheat varieties with relatively good winter hardiness. Averaged over eight years, the results prove that T. durum genotypes are now available whose average state of hardening and winter hardiness are equal or better than those of winter T. aestivum varieties with moderate frost resistance.
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.
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.
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.
The transitions between various developmental phases are critical in determining the ecological adaptation and yield of cereals. In order to elaborate a methodology for establishing the timing of the consecutive plant developmental phases from germination to the fully developed plant, regular measurements of changes in developmental components were carried out on one winter (Kompolti Korai) and one spring (Morex) barley cultivar in a model experiment. Under the controlled environmental conditions linear regression was characteristic of the associations between the chronological time and all or most of the time course data of plant height, tiller and leaf numbers. The initial growth of the spring barley was twice as intensive as that of the winter barley. The length of the stem elongation phases was similar for the two varieties, but the winter barley cultivar showed significantly more intensive stem growth compared to the spring barley. The spring barley reached all the plant developmental phases significantly earlier than the winter barley. For both cultivars, tillering continued till after first node appearance and there was a definite delay between first node appearance and the beginning of the stem elongation phase. The determination of the full series of phenophases, together with the evaluation of various yield components on the same plant, provide an excellent way of establishing plant developmental patterns and may make a significant contribution to achieving a better understanding of the associations between plant developmental patterns and the adaptation and yielding ability of cereals.
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.
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.
