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The objective of this study was to develop an understanding about the genetics of terminal heat tolerance in wheat (Triticum aestivum L.). The minimum number of genes was assessed using Mendelian and quantitative genetic approach. Two crosses were made between heat tolerant and heat susceptible bread wheat cultivars: NW1014 × HUW468 and HUW234 × HUW468. Heat susceptible HUW468 was common in both the crosses. The F4, F5 and F6 generations were evaluated including F1 in two different dates of sowing (normal and very late) under field conditions in year 2006–07. The data was recorded for grain fill duration (GFD) and thousand-grain weight (TGW). Based on data of two dates, decline% and heat susceptibility index (HSI) of GFD and TGW were estimated. Heat tolerance in F1 showed absence of dominance. Estimation of genes using Mendelian approach in F4, F5 and F6 progenies (148–157) of the two crosses suggested that heat tolerance was governed by a minimum of three genes. Quantitative approach also indicated similar number of genes. The distribution of progeny lines in F4 and F6 supported the polygene nature of heat tolerance. These genes if mapped by molecular approach can play an important role through marker assisted selection (MAS) for developing improved thermo-tolerant lines of wheat.

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Heat stress is an important production constraint of wheat during grain-fill period in India and in other parts of the world where the temperature become high during anthesis to maturity (grain-filling) stage of plant growth. This study determined the genetic control of heat tolerance through half diallel analysis of selected wheat genotypes. Heat induced damage of plasma membrane was assayed by membrane thermo-stability (MTS), which measure electrolyte leakage from leaf tissues after exposure to high temperature. Eight genotypes comprising heat tolerant and sensitive response to high temperature stress were hybridized in a half diallel. Electrolyte leakage or MTS was conducted at grain-filling stage of plant growth as ambient temperature become high enough to cause heat hardening of leaves. The mean square for GCA was higher in magnitude than that of SCA, but the components of genetic variance indicated considerable influence of dominance variance in determining inheritance of this trait. Results suggested that the selection for heat tolerant inbred lines based on MTS in this material may be more effective by reducing the dominance variance after a few generation of selfing particularly in a self-pollinated wheat crop. The varieties, Hindi 62 and NIAW 34 were good general and specific combiners in the tolerant group, while HD 2687 and WH 147 were good specific combiners in the heat sensitive group.

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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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Sarkar, C.K.G., Srivastava, P.S.L., Deshmukh, P.S. 2001. Grain growth rate and heat susceptibility index: Traits for breeding genotypes tolerant to terminal high temperature stress in bread wheat ( Triticum aestivum L.). Indian J. Genet. 61 :209

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Sarkar, C.K.G., Srivastava, P.S.L., Deshmukh, P.S. 2001. Grain growth rate and heat susceptibility index: Traits for breeding genotypes tolerant to terminal high temperature stress in bread wheat ( Triticum aestivum L.). Indian J. Genetics and Plant

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147 156 Mason, R.E., Mondal, S., Beecher, F.W., Pascheo, A., Jampla, B., Ibrahim, A.M.H., Hays, D.B. 2010. QTL associated with heat susceptibility index in wheat ( Triticum

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Hossain, A., Teixeira da Silva, J.A., Lozovskaya, M.V., Zvolinsky, V.P., Mukhortov, V.I. 2012. High temperature combined with drought affect rainfed spring wheat and barley in south-eastern Russia: Yield, relative performance and heat susceptibility index

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