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Terminal heat referred to as increase in temperature during grain filling, is one of the important stress factors for wheat production and is responsible for decline in wheat production in many environments worldwide. In order to meet the challenges of high temperature ahead of global warming, concerted efforts are needed to evaluate wheat genotypes for heat tolerance and develop genotypes suitable for such stressed environments. Twenty-seven advanced wheat genotypes developed for stress and normal environments by different research centres were evaluated during 2009–10 and 2010–11 under timely sown (normal) and late sown (heat stress) environments. Analysis of variance revealed that the genotypes differed significantly in grain filling duration (GFD), grain growth rate (GGR) and thousand-grain weight (TGW). Out of 27 genotypes, 16 were found to be tolerant for thousand-grain weight under late planting (heat stress) during 2009-10 but only 12 were tolerant during 2010–11. Many of the genotypes registered more reduction in thousand-grain weight during 2010–11 as compared to 2009–10; the temperatures during 2009–10 were higher. The differences in grain filling duration under two conditions during both seasons as well as difference in temperatures during first half of grain filling explain the reduction pattern in the genotypes. GFD had significant negative correlation with temperatures during post heading period and the difference in GFD under two environments had positive correlation with these temperatures. The reduction in GFD had regression of 33.3% on reduction in GGR and reduction in GGR had regression of 41.6% on reduction in TGW genotypes AKW 1071, DBW 17, HS 277, K 7903, K 9107, NW 1014 and RAJ 3765 had less sensitivity to stress environments during both years.

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A set of ten durum wheat genotypes was grown in experiments conducted under four contrasting Mediterranean conditions during three years to assess the effect of latitude and water regime on grain growth and grain yield formation. The relationship between grain weight and accumulated growing degree-days (GDD) from anthesis was described by a logistic equation and final grain weight ( W ) and maximum rate ( R ) and duration ( D ) of grain filling were calculated from the fitted curves. Thousand kernel weight (TKW) was positively related to grain yield at both latitudes and water regimes, although the contribution of the number of grains per m 2 to final yield was only significant in the south, where environmental constraints likely limited the achievement of a large grain set. Differences in final grain weight between latitudes could be mostly explained by differences in the grain filling rate, while changes on W between water regimes were due to altered grain filling durations. Under northern conditions grain yield was positively associated to grain filling duration but negatively related to the maximum rate of grain filling, while in the south the coefficients of the grain filling curves had little or no effect on final yield. Reductions in grain yield under rainfed conditions were due to the fall in the number of grains per m 2 since TKW was not significantly affected by drought.

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Cereal Research Communications
Authors: M. Mirosavljević, V. Momčilović, P. Čanak, D. Trkulja, S. Mikić, B. Jocković and N. Pržulj

Knowledge about the comparative development and grain filling of winter cereals under different environmental conditions is important for stable and high yielding crop production. The objective of this work was to compare patterns of grain filling in bread wheat, barley and triticale grown in the Pannonian region, as well as to investigate relationships among grain filling parameters, time to anthesis and grain yield. The trials with 12 winter cereal genotypes were carried out in four successive seasons at the location Novi Sad, Serbia. Results of this study showed that all studied grain filling parameters were significantly influenced by species, cultivar, growing season, and species by growing season interaction. Longer duration of grain filling period and period to maximum grain filling were observed in triticale and wheat cultivars compared with six and two-rowed barley. Two-rowed barley cultivars had a higher grain filling rate than other cultivars. Furthermore, a negative association between time to anthesis and grain yield indicates that cultivars with the long preanthesis period are not recommended for the agro-ecological conditions of the Pannonian plain. Generally, medium early cultivars of small grain cereals had the highest grain weight within species and spike type, suggesting that medium early cultivars have a balanced ratio of pre-anthesis and grain filling period. High values of final grain weight in different growing seasons indicate that weather conditions in the Pannonian plain are mainly suitable for grain growth.

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High temperature is a major determinant of wheat development and growth and causes yield loss in many regions of the world. This study was conducted to assess heat stress effects on yield and yield related traits of wheat. The 144 recombinant inbred lines derived from the cross of Kauz (heat tolerant) and MTRWA116 (susceptible) together with some commercial cultivars were evaluated during 2006–2007, 2007–2008 under normal and heat stress (late sowing) conditions. Grain yield, head length, kernels per spike, spiklets per spike, plant height, grain filling duration, peduncle length and 1000 kernels weight were measured. The results showed a significant difference among RILs for all traits in stress and control conditions. High temperature significantly decreased all traits specially grain yield (46.63%), 1000-kernel weight (20.61%) and grain filling duration (20.42%). Grain yield was most affected and spikelets per spike was least affected (11.77%). Grain yield under heat stress was directly correlated (r = 0.49) with yield in normal condition. Head length and grain yield had the highest (93.18%) and the lowest (62.97%) heritability, respectively. Peduncle length and grain filling duration showed the highest correlation with yield under both normal and heat stress conditions suggesting that these two traits could be used as reliable screening tools for development of heat-tolerant genotypes.

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Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. The aim of this study was to investigate the effect of short periods of high temperature, drought and their combination at different growth stages of plant under controlled conditions. The effects of high temperature and drought on grain yield were additive. However, high temperature increased the degree of water stress and the combined effects of drought and high temperature were much more severe than those of each individual treatment. High temperature and drought applied at post- anthesis shortened duration of maturation, grain filling duration and reduced grain yield, mean grain weight, grain number and thousand-grain weight.

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Cereal Research Communications
Authors: S. Sareen, N. Bhusal, G. Singh, B.S. Tyagi, V. Tiwari, G.P. Singh and A.K. Sarial

Heat stress is a matter of a great concern for the wheat crop. Heat stress usually either hastens crop development or shortens the grain filling duration, which severely reduces grain yield. Being a complex trait, understanding the genetics and gene interactions of stress tolerance are the two primary requirements for improving yield levels. Genetic analysis through generation mean analysis helps to find out the nature of gene actions involved in a concerned trait by providing an estimate of main gene effects (additive and dominance) along with their digenic interactions (additive × additive, additive × dominance, and dominance × dominance). In the present investigation, we elucidated the inheritance pattern of different yield contributing traits under heat stress using different cross combinations which could be helpful for selecting a suitable breeding strategy. Thus six generations of five crosses were sown normal (non-stress, TS) and late (heat stress, LS) in a randomized block design with three replications during two crop seasons. The model was not adequate for late sown conditions indicating the expression of epistatic genes under stress conditions. The traits i.e. Days to heading (DH), Days to anthesis (DA), Days to maturity (DM), Grain filling duration (GFD), Grain yield (GY), Thousand grain weight (TGW), Grain weight per spike (GWS) and Heat susceptibility index (HSI) under heat stress conditions were found under the control of additive gene action with dominance × dominance interaction, additive gene action with additive × dominance epistatic effect, dominance gene action with additive × additive interaction effect, additive and dominance gene action with dominance × dominance interaction effect, additive gene action with additive × dominance epistatic effect, additive gene action with additive × additive interaction effect and dominance gene action with additive × additive interaction effect, respectively.

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Field cultivation practices affected soil temperature that influenced the crop development of winter crops. This study was undertaken to determine the effects of different mulch materials, tillage depths and planting methods on spike differentiation of winter wheat ( Triticum aestivum L.). The field experiment was consisted of three tests: (i) polythene mulch, straw mulch and no mulch; (ii) ridge planting and furrow planting; (iii) conventional tillage and shallow tillage. The results showed that soil temperature was affected by different practices. The higher soil temperature under polythene mulch resulted in the earlier initiation of spike differentiation, while straw mulch decreased soil temperature in spring that delayed the initiation compared with the non-mulch treatment. The spike initiation under ridge planting started earlier than that of furrow planting. Reduced tillage delayed the initiation compared with the conventional tillage. Duration of spike differentiation lasted longer under earlier starting of initiation that increased the grain numbers per spike. Other yield component characters were not affected by soil temperature. It was concluded that in the North China Plain where grain-filling duration of winter wheat was limited, agricultural practices that increased soil temperature in spring were favorable for grain production.

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A study was conducted during 2008–2010, to estimate heterosis for yield component traits and protein content in bread wheat under normal and heat-stress environment by utilizing a set of 45 half diallel cross combinations, involving 10 diverse parents. Analysis of variance revealed significant differences for the two environements, whereas differences over the years were non-significant for all the traits. The pooled data over the years, exhibited highly significant differences for all the traits under both normal and heat-stress environments. The number of tillers/plant exhibited maximum degree of standard heterosis under normal and heat-stress environment (with value of 12.62% and 53.75%), respectively. In general, spike length (16.02%) and number of grains/spike (52.10%), showed higher magnitude of standard heterosis under normal environment than heat-stress environment, whereas number of tillers/plant (53.75%) and gain filling duration (43.68%) showed higher standard heterosis in heat-stress environment than the normal one. For grain yield/plant, 1000-grain weight and protein content, the number of cross combination showing standard heterosis were almost same in both the environments. The ten crosses, out of forty-five crosses, namely HD 2733/WH 542; PBW 343/UP 2425; HD 2687/PBW 343; PBW 343/UP 2382; PBW 343/HD 2285; WH 542/UP 2425; PBW 343/PBW 226; UP 2382/HUW 468; PBW 343/WH 542 and PBW 226/HD 2285 can be used to select transgressive segregants for normal as well warmer wheat growing areas. These ten combinations can be used by involving, the trait grain filling duration, tillers per plant, spike length, grains per spike, 1000-grain weight to improve grain yield for warmer areas. In all 45 cross combinations, six cross combinations were identified for better per se performance for grain yield as well as protein content under heat-stress environment. These combinations may thus be used for developing superior genotypes through fixation of heterosis are also supported by high SCA. Besides, results of present study also revealed ample scope for developing transgressive segregants involving some of these parents to develop high yielding genotypes in wheat suitable for heat stress environments.

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