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To evaluate the genetic background of quantitative criteria of drought tolerance in wheat, six generations of a cross between the varieties of Plainsman and Cappelle Desprez were grown in a randomized complete block design with three replications in the greenhouse of the College of Agriculture of the University of Tehran in 1997. Genetic variation was found for yield potential (Yp), stressed yield (Ys), excised leaf water retention (ELWR), relative water loss (RWL), relative water content (RWC) and harvest index (HI) under water stress conditions. High heterosis and heterobeltiosis were observed in the F1 hybrid for Ys, HI and spike yield index (SYI). Genetic analysis exhibited overdominance in the inheritance of Ys, RWL, ELWR, HI, biomass and SYI, while RWC and Yp were controlled by the additive type of gene action. High narrow-sense heritability estimates were shown by ELWR, biomass and SYI. The high genetic advance for ELWR, RWC, HI and SYI indicated that direct selection could be effective for these traits. The epistatic effects (additive × additive=[i] for Yp, Ys and RWL, additive × dominance=[j] for ELWR, and dominance × dominance =[l] for RWL) were found to be outstanding.

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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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Gene effects were analysed using mean stomatal number and specific leaf weight of 12 populations, consisting of both parents (P 1 and P 2 ), F 1 , F 2 , first backcross generations (BC 1 and BC 2 ), second backcross generations (B 11 , B 12 , B 21 , B 22 ) and backcross selfed generations (B 1 s and B 2 s) of four crosses involving three drought-tolerant and three drought-susceptible cultivars of Triticum aestivum L. to determine the nature of gene action governing stomatal number (SN) and specific leaf weight (SLW) through generation mean analysis in moisture stress (E 1 ) and moisture non-stress (E 2 ) environments. The digenic epistatic model was found to be inadequate for stomatal number and the additive-dominance model was found to be adequate for specific leaf weight in most of the crosses. Additive gene effects were predominant for SLW, while for SN both additive and dominance components of variance were important. Epistatic effects, particularly the additive × dominance (j) type of interaction, were present for both the characters. The duplicate type of epistasis was observed for stomatal number in the cross VL421/HS240 in the moisture stress environment. Significant heterosis was observed for the crosses Hindi 62/HS240 and VL421/HS240 over the standard check (SC) in the moisture stress environment (E 1 ) for both the characters. Genotype-environmental interactions and/or differential gene expression appeared to account for the different results found between environments. Hybridization systems, such as biparental mating and/or diallel selective mating, could be useful for the improvement of these traits, which would help in identifying drought-tolerant progenies.

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Gene effects were analyzed using mean excised-leaf water loss and relative water content of 12 populations viz., both parents (P 1 and P 2 ), F 1 , F 2 , first back cross generations (BC1 and BC2), second back cross generations (B 11 , B 12 , B 21 , B 22 ) and back cross-selfed generations (B 1 s and B 2 s) of four crosses involving three drought tolerant and three drought susceptible cultivars of Triticum aestivum L. to determine nature of gene action governing excised-leaf water loss (ELWL) and relative water content (RWC) through generation mean analysis under rainfed (E1) and irrigated (E2) environments. Both additive-dominance and digenic epistatic model were found to be inadequate in all the crosses for ELWL and in most of the crosses for RWC to explain genetic variation among the generation means. Additive gene effects were predominant for RWC, while for ELWL both additive and dominance component of variance were important. Epistatic effects, particularly dominance × dominance (1) type of interaction was more predominant for RWC, while additive × additive(i) for ELWL. Duplicate type of epistasis was observed in the crosses Hindi 62/HS240 and VL421/HS240 for RWC and in the cross S4/HPW89 for ELWL under both the environments. Complementary type of epistasis was observed only in the cross VL421/PBW175 for ELWL under E1. Hybridization systems, such as biparental mating and/or diallel selective mating could be useful for improvement of these traits which would help in isolating drought tolerant progenies.

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analysis for yield and its component traits in barley ( Hordeum vulgare L.). Indian J. Genet. , 65 , 129–130. Sharma A. K. Generation mean analysis for yield and its

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. A., Rao, A. M., Savithramma, D. L., Madhusudan, K. (1995): Generation mean analysis in sesame. Crop Improvement , 22, 237-240. Generation mean analysis in sesame Crop Improvement

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Crop Sci. 32 723 728 Farshadfar, E., Ghanadha., M., Zahravi, M., Sutka, J. 2001: Generation mean analysis

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Mullaney, E.J., Martin, J.M., and Scharen, A.L. 1982. Generation mean analysis to identify and partition the components of genetic resistance to Septoria nodorum in wheat. Euphytica 31:539–545. Scharen A

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, Z. , Milka , B.J. , Savic , D. , Zdravković , M. , and Cvikic , D. ( 2011 ). Generation mean analysis of yield component and yield in tomato ( Lycopersicon esculentum Mill.) . Pakistan Journal of Botany , 43 : 1575 – 1580 .

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