Epistatic Gene Effects Research Articles

Generation Mean Analysis for quantitative traits in the population of AKDRMS 21-54 x YH3 cross of rice (Oryza sativa L.)

Aim: To study the genetic components of inheritance for 12 quantitative traits which leads into genetic improvement by identification of gene actions for yield and yield related traits. Methodology: Twelve quantitative traits for yield and yield attributing traits were studied at Agricultural College, Bapatla during Rabi 2021-22 deploying Hayman's five parameter model generation mean analysis in estimating the gene effects in the population (P1, P2, F1, F2 and F3) generated from the cross AKDRMS 21-54 x YH3. Estimated mean effects affirm the existence of significant variation in the traits studied. Significance of either one or both, scales C or D inferred the existence of epistatic interaction for the traits studied. Digenic non-allelic interaction model explained the gene action of the traits studied in the present investigation. Results: The generation mean for all the traits showed the importance of both additive and dominance type of gene effects. Among the epistatic gene effects, the additive x additive gene interaction was reported predominant for shoot length, plant height, flag leaf length, spikelet fertility and flag test weight. The gene interaction is associated with homozygosity, therefore, pedigree method of breeding may be adopted for isolation of desirable lines, while for all other traits, along with grain yield per plant, dominance x dominance gene interaction was found to be pre-dominant. The gene interaction is not fixable, hence, population improvement approaches, would be effective. Interpretation: Dominance x dominance gene interaction was predominant for grain yield per plant and majority of yield component traits studied coupled with duplicate epistasis, infers to takeup population improvement approaches, such as bi-parental mating and recurrent selection, followed by isolation of purelines in later generations for competent improvement. Key words: Epistasis, Five parameter model, Generation Mean Analysis, Quantitative traits, Rice

Genetic analysis of grain yield and its contributing traits in four bread wheat (Triticum aestivum L.) crosses using six parameter model

In order to create a successful and efficient breeding programme, it is highly helpful to analyse the gene action governing the expression of different traits. The objective of the present study was to use generation mean analysis to ascertain the kind and extent of gene action in bread wheat utilizing six generations (P1, P2, F1, F2, BC1 and BC2) of the four crosses, cross I (HD 2967 x PBW 752), cross II (RSP 561 x PBW 779), cross III (RSP 561 x PBW 780), and cross IV (JAUW 584 x WH 1184). These crosses included elite stripe rust resistant wheat genotypes in addition to locally adapted cultivars. The results showed that all the traits in all crosses had highly significant estimated mean effects (m), showing the quantitative inheritance of the selected traits. For grain yield and most of the selected characters, it was found that additive gene effects was shown to be less significance than dominance type gene effects. Among the different characters studied in the four crosses, the degree of dominance x dominance was large and negatively significant, whereas additive x additive gene actions were high and positively significance. In wheat breeding, it was found that selection for the improvement of grain yield and its contributing traits must be postponed until later generations because additive x dominant gene effects was of lesser significance. Keywords:  wheat; grain yield; additive; dominance; epistatic gene effects

TRIPLE TEST CROSS ANALYSIS FOR DETERMINING GENE ACTION, GENETIC CORRELATIONS AND PREDICTION FOR YIELD AND YIELD COMPONENTS IN BREAD WHEAT

In two crosses of bread wheat (Gemmeiza11 x Misr1 and Gemmeiza12 x Misr2) to investigate gene action, genetic correlations and predicating new recombinant lines for days to heading, plant height, flag leaf area, number of spikes/plant, number of grains/spike, 1000-grain weight, spike grain weight and grain yield /plant, triple test cross was used. The starting materials for triple test cross was the F1 and their grand parents (P1 and P2) for the two studied wheat crosses. The first cross Gemmeiza 11 x Misr1 and the second cross was Gemmeiza 12x Misr2. The F1’s were selfed to produce F2’s grains. In order to create F1 and F2 plants, the obtained materials (F1 and F2 grain genotypes) and the parental genotypes were seeded together. Thirty individual F2 plants were randomly labeled from each cross and crossed back to their grand parents (P1 and P2) and F1 between then to produce three types of families L1 (F2i x P1i), L2 (F2i x P2i) and L3 (F2i x F1i) in each cross. On November 10, 2018, during the winter growing season, the triple test cross families (L1, L2 and L3), along with the parents, F1 and F2 in each cross, were seeded. Results showed that in the genetic system for the investigated features for two crosses, epistatic gene effects were significant. The types of epistasis (additive x additive, additive x dominance and dominance x dominance) were significant for all studied characters. For the majority of traits in both crossings, both additive and dominant genetic components were significant and involved in the genetic system. The average level of dominance for spikes/plant in cross 1 and spike grain weight in cross -2 was overdominance, while for the remaining characters, additive gene effects were more pronounced. The F value was positive and significant for 1000-grain weight in two crosses, suggesting that dominant genes controlling these characters were unidirectional. The highest proportion of inbreds excepted to outperform parental rang in cross 1 for days to heading and flag leaf area. In both crosses, grain yield per plant was positively and significantly correlated with number of spikes per plant, number of grains per spike, and 1000-grain weight, according to epistasis, additive, and dominance genetic correlations.

Genetic analysis of salinity tolerance in wheat (Triticum aestivum L.).

Understanding the genetics of salt tolerance is of utmost need to combat the rising prevalence of soil salinity through employing tolerant cultivars. The current study was carried out to investigate the quantitative genetic basis of agronomical and physiological-related traits of salinity-stressed plants using seven generations (parental cultivars, F1, F2, F3, BC1, and BC2) of wheat grown in the field under normal and saline conditions. The combined analysis of variance showed highly significant effects of salinity and genotypes (generations) on all the traits. The scaling tests did not support the three-parameter model (additive-dominance model); hence, the six-parameter model was used to assess the genetic effects governing the traits in this study. The epistatic gene effects were crucial, as were additive and dominance gene effects for plant height, K/Na, and yield in salinity stress conditions. The highest heritability was observed for total chlorophyll, carotenoid, SPAD chlorophyll, and K/Na ratio in saline conditions. The additive genetic variance was more important than the dominance variance for grain weight, K, K/Na in salinity conditions. The findings of the current study may have important implications in the quantitative genetics of salinity tolerance and the development of cultivars tolerant to salinity in wheat.

Dijalelna analiza nauta

This research was carried out at Dicle University, Faculty of Agriculture during the spring season in 2020. Four chickpea varieties (Cagatay, ILC 3279, Ak 71114 and Spanish chickpea) were used. Genetic parameters were estimated for plant and agricultural traits in 4 parents and their 6 F2 combinations obtained from their half-diallel crossbreeding in chickpea. Half diallel genetic parameters, ratios and graphs (Vr,Wr) were estimated using to methods of Hayman (1954a, 1954b, 1960) in the experiment. The study was carried out randomized complete blocks design with three replications. In the study, days to first flowering, plant height, internode length, the first flower node number, internode thickness was examined. Analysis of variance revealed that differences among genotypes were significant for days to first flowering days, plant height and first flower node number. However, internode length, 5th, 7th and 9th internodes thickness were nonsignificant. Dominant allele genes are more than the recessive allele genes in the days to first flowering, plant height and first flower node number. Epistatic gene effects were significant in the parents for days to first flowering. Cagatay and ILC 3279 had mostly dominant genes, but Ak 71114 had recessive genes. Additive genetic variance was significant for days to first flowering, plant height and internode length. Internode length for parents was mostly recessive genes, especially Spanish and Ak 71114. The dominant gene effect was significant for the first flower node number. In the narrow sense heritability degree was 42% for plant height and 45% for days to first flowering.

English

Common beans are an important nutritious food crop to many people in developing countries. Inadequate soil-P is one of the major constraints to high bean seed yield productivity. Information about genetic effects that control inheritance of root traits in common bean grown under low soil-P conditions is scarce, and that is a challenge for genetic enhancement. This study was therefore implemented to determine inheritance and gene action of root traits in common bean for tolerance to low soil-P. The six generations were evaluated in a completely randomised design with two replicates under low soil-P in a pot experiment. Generation mean analysis revealed that both allelic and non-allelic genetic interactions controlled inheritance of root traits studied. Cumulative main gene effect was higher than epistasis effects. Additive genetic effects were more predominant than dominance effects. Additive and additive × dominance epistatic gene effects were more important in controlling inheritance of root traits under low soil-P. Broad-sense heritability for hypocotyl root number was the highest (93.98 %) while the narrow-sense heritability was moderate (51.13 %). To develop improved genotypes tolerant to low soil-P, recombination crossing should be followed by screening and selection in later generations for high seed yield, root and other preferred traits. Key words: Common bean, inheritance, genotype, gene effect, heritability, low soil-P.

Inheritance of Pod Length and Other Yield Components in Two Cowpea and Yard-Long Bean Crosses

This study determined the gene effects involved in the inheritance of pod length and other yield-related traits and relationships among traits in crosses between two cowpea lines (TVu 2280 and TVu 2027) and a yard-long bean (TVu 6642) line with long pods. Plants of six generations (P1, P2, F1, F2, BC1P1, and BC1P2) derived from TVu 2280 × TVu 6642 and TVu 2027 × TVu 6642 were evaluated under field conditions. Data collected on 14 yield components of each cross were used for generation mean analysis. Gene effects and their magnitudes varied with the crosses; digenic epistatic gene effects were detected for 10 traits in TVu 2280 × TVu 6642 and 11 traits in TVu 2280 × TVu 6642. Only additive gene effect was significant for pod length in TVu 2280 × TVu 6642 while additive, dominant, and two of the three digenic epistatic gene effects were significant in TVu 2027 × TVu 6642. Models that incorporated only significant additive, dominant, and digenic epistasis were adequate for all 14 traits in TVu 2280 × TVu 6642 and eight of the 12 traits in TVu 2027 × TVu 6642 for which model-fitting was possible. Across segregating generation of the two crosses, pod length (PodLNT) was significantly (p < 0.001) correlated with three major yield components viz. pod weight (0.84, 0.77), number of seeds per pod (0.41, 0.30) and seed weight per pod (0.61, 0.29). Significant correlation of PodLNT with seed yield per plant was moderate and significant (p < 0.01–0.001) in the BC1P1 of the two crosses (0.31 and 0.41). An improvement in cowpea seed yield is feasible through selection for long pods in segregating generations involving crosses with yard-long bean.

Heterosis for egg production in native by exotic by inbred chicken crosses

Inbred lines generated from the native and exotic chickens were compared with their F1 and backcross populations for a range of short term egg production traits. The experimental birds were brooded for 8 weeks and raised on a deep litter pens from 8 to 40 weeks of age. Age at first eggs were longer in the crossbred groups and the delay was mostly caused by the dominant genes from the exotic parents. Highly significant (P>0.01) heterosis were obtained by the crossbred groups in hen day rate and total egg mass respectively. The heterosis observed in the crossbred groups for egg weight was low and mostly non significant. the backcross groups recorded residual heterosis in egg production traits ( hen day rate, total egg mass and egg weight) and the magnitude was higher in the exotic than the native backcrosses. The results further indicate that the egg production performance of the crossbred groups were mostly influenced by maternal, sex linked, dominance and epistatic gene effects. It was suggested that the egg production potential of the native chicken could be improved further by cross mating-selected native and exotic backcross groups. This should be followed by crisscrossing.

The combining ability of new lines of cucumber for the main economically valuable traits

Relevance.To create heterotic cucumber hybrids, it is important to have a high general and specificcombining ability of the initial material, which makes it possible to select valuable genotypes at anearly stage of selection.Material and methods.The research was carried out in 2018-2020. at the Research Institute ofVegetable, Melon Crops and Potatoes, located in the Tashkent region of Uzbekistan (SRIVMC&P).Studied 6 accessions of cucumber. As a result of diallelic crosses, 36 hybrid combinations wereobtained (p2). Hybridological analysis was carried out according to the first Griffing's method, including forward and backcrossing and the use of parental forms (p2). To determine the combining ability,conventional methodologies were used (1,15). Genetic-statistical analyzes were carried out usingthe MS Excel application package.Results.Studies have established that according to the traits "the number of days from seed germination to the opening of female flowers" and "the number of days until the technical ripeness offruits" in all studied cucumber accessions, the ratio (σ2ĝi<σ2si) is observed, where the dominant rolein the inheritance of this trait also belongs to genes with dominant and epistatic effects. The trait“number of fruits per plant” is controlled by dominant and epistatic gene effects (σ2ĝi<σ2si) in almostall cucumber accessions, and in the accession A-6 - by additive gene effects (σ2ĝi<σ2si). Thephenomenon (σ2ĝi<σ2si) was noted for the trait "average fruit weight", where the expression of thetrait is controlled by the dominant and epistatic effects of genes (σ2ĝi<σ2si) in three studied cucumber accessions (C-25/1, A-6 and A-9), and in the other three accessions, additive gene effects (σ2ĝi<σ2si) are more important in inheritance. The trait "productivity of one plant" is controlled by the dominant and epistatic effects of genes (σ2ĝi<σ2si) in the three studied cucumber accessions, and in theother three accessions (C-25/1, A-6 and A-9), genes play a special role for the expression of the traitwith additive effects. Promising hybrid combinations with the best performance for their use as a initial material for breeding have been revealed.

Genetics of resistance to Fusarium stalk rot caused by Fusarium verticilloides in maize (Zea mays L.)

Fusarium stalk rot disease (FSR), incited by Fusarium verticilloides, is becoming an important biotic production constraint in many major maize growing areas causing substantial yield losses. The present investigation was conducted to understand the genetics of resistance to FSR through six generation means and variances, as a first step in addressing the problem. Five crosses were developed by crossing four FSR susceptible inbreds (VL1043, VL108867, VL121096 and VL1218) with two resistant inbreds (CM202 and CM212). Six generations of the five crosses (VL1043 × CM212, VL108867 × CM202, VL121096 × CM212, VL1218 × CM202 and VL1218 × CM212) were evaluated through artificial disease inoculation during post rainy season of 2018 and summer, 2019. The scaling tests and joint scaling tests indicated the inadequacy of additive-dominance model and showed the presence of epistatic gene effects in all the five crosses for FSR resistance. The study further revealed the importance of additive, dominance and additive × additive gene effects in the expression of FSR. The magnitude and direction of the additive genetic effects [a], dominance genetic effects [d], magnitudes of additive genetic variance (2A) and dominance genetic variance (2D) varied with the genetic background of the crosses over seasons. Duplicate gene interaction was evident in the inheritance of FSR resistance. Both, additive and non-additive components were found important thus reciprocal recurrent selection would be more effective in obtaining FSR resistant maize inbred lines.

THE ROLE OF NON-ALLELIC INTERACTION IN INHERITANCE OF SOME ECONOMIC TRAITS IN G. BARBADENSE

The triple test cross analysis was used to study different components of genetic variation by using 75 triple test cross families and their parents, F1 and F2 in one cotton cross (Giza 95 x Australy) for yield, its components and fiber quality traits. The 75 TTC families (25L1, 25L2 and 25L3) were sown at Sakha Experimental Station; Agriculture Research Center, Kafr El-Sheikh government; Egypt. Mean squares between L1, L2 and L3 were highly significant for all traits studied, while between L1 and L2 Families found to be significant for boll weight, lint percentage, lint index, fiber length and micronaire reading. Overall epistatic gene effects were highly significant differences for all traits studied except for fiber length and fiber strength. The (i) fixable type (additive × additive) was the most important epistatic effect than j and 1 non-fixable type for all traits. Both additive and dominance components were highly significant for all the traits studied. The degree of dominance was less than unity and confirmed the presence of partial dominance for all traits studied except for lint yield/plant; lint index and seed index were over-dominance. The Additive gene action played an important role in controlling inheritance for all traits studied than dominance one except for lint yield/plant; lint index and seed index. Direction of dominance (r) was non-significant for most traits indicating absence of dominance directional. Due to influence of (i) type of epistatic effects for the majority of the studied traits selection in early generations may be recommended. Genotypic correlation was positive and significant between yield traits and its components. This could help cotton breeder to use indirect selection to increase yield traits. All the studied traits showed higher proportion of recombinants inbreds falling outside parental range nearly 40%. So, these higher values of prediction revealed that it would be feasible to predict as early as possible for transgressive segregation which can surpass parental range for most studied traits.

THE ROLE OF NON-ALLELIC INTERACTION IN INHERITANCE OF SOME ECONOMIC TRAITS IN G. BARBADENSE

The triple test cross analysis was used to study different components of genetic variation by using 75 triple test cross families and their parents, F1 and F2 in one cotton cross (Giza 95 x Australy) for yield, its components and fiber quality traits. The 75 TTC families (25L1, 25L2 and 25L3) were sown at Sakha Experimental Station; Agriculture Research Center, Kafr El-Sheikh government; Egypt. Mean squares between L1, L2 and L3 were highly significant for all traits studied, while between L1 and L2 Families found to be significant for boll weight, lint percentage, lint index, fiber length and micronaire reading. Overall epistatic gene effects were highly significant differences for all traits studied except for fiber length and fiber strength. The (i) fixable type (additive × additive) was the most important epistatic effect than j and 1 non-fixable type for all traits. Both additive and dominance components were highly significant for all the traits studied. The degree of dominance was less than unity and confirmed the presence of partial dominance for all traits studied except for lint yield/plant; lint index and seed index were over-dominance. The Additive gene action played an important role in controlling inheritance for all traits studied than dominance one except for lint yield/plant; lint index and seed index. Direction of dominance (r) was non-significant for most traits indicating absence of dominance directional. Due to influence of (i) type of epistatic effects for the majority of the studied traits selection in early generations may be recommended. Genotypic correlation was positive and significant between yield traits and its components. This could help cotton breeder to use indirect selection to increase yield traits. All the studied traits showed higher proportion of recombinants inbreds falling outside parental range nearly 40%. So, these higher values of prediction revealed that it would be feasible to predict as early as possible for transgressive segregation which can surpass parental range for most studied traits.

Genetic Studies on the Inheritance of Storage-Induced Cooking Time in Cowpeas [Vigna unguiculata (L.) Walp

Cowpeas provide food and income for many small-holder farmers in Africa. Cowpea grains contain substantial quantities of protein, carbohydrates, vitamins, and fiber. In areas where subsistence farming is practiced, cowpea’s protein is cheaper than that obtained from other sources such as fish, meat, poultry or dairy products and combines well with cereal grains in diets. However, long-cooking times, typical of many grain legumes, is a major limitation to the utilization of cowpeas especially among the low-income and growing middle-income population of Africa. Long periods of cooking cowpeas lead to loss of nutrients, loss of useful time and increased greenhouse gas emission through increased burning of firewood. Fast-cooking cowpeas has the potential to deliver highly nutritious food to the hungry within shorter periods, encourage less use of firewood, improve gender equity, increase the consumption of cowpeas, trigger an increase in demand for cowpeas and thus incentivize cowpea production by smallholder farmers in Sub-Saharan Africa. In this study, the inheritance of storage-induced cooking time in cowpeas was investigated. Two sets of bi-parental crosses were conducted involving three cowpea genotypes: CRI-11(1)-1, C9P(B) and TVu7687. Generation means from six generations were used to determine the phenotypic and genotypic variances and coefficients of variation. Broad and narrow sense heritabilities and genetic advance percentage of mean were estimated. Generation mean analysis showed that additive, dominant, additive–additive, additive–dominant, and dominant–dominant gene actions were significant (p < 0.001). Fast-cooking trait was dominant over the long-cooking trait. Broad sense heritability for crosses C9P(B) × CRI-11(1)-1 and TVu7687 × CRI-11(1)-1 were 0.94 and 0.99 respectively while narrow sense heritabilities were 0.84 and 0.88 respectively. Genetic advances were 27.09 and 40.40 respectively. High narrow-sense heritabilities and moderate genetic advance for the fast-cooking trait indicated the presence of additive genes in the trait and the possibility of introgressing the trait into farmer-preferred varieties using conventional selection methods. However, due to significant epistatic gene effects observed, effective selection for fast-cooking trait would be appropriate at advanced generations.

Genetic study for epistatic gene effects for major yield contributing traits against drought in rice

The study subjected to estimate gene effects and inheritance of quantitative traits of rice with Generation Mean Analysis (GMA). Segregation analysis and estimation of genetic parameters under epistatic model indicated partial dominance and importance of additive effects in the inheritance of drought tolerance, respectively. In present study, absence of epistasis by scaling tests was recorded only for plant height in cross NDR-359 x P0 1564, grains per panicle in cross DSL- 63-8 x NDR- 359, test weight in cross Sarjoo-52 x P0 359, harvest-index in cross NDR-359 x P0 1564 and spikelets per panicle in cross Sarjoo-52 x P0 359 and NDR-359 x P0 1564 in irrigated condition and days to 50 per cent flowering in cross P0 359 x Sonam and harvest-index in cross NDR-359 x P0 1564 in drought condition. In remaining cases, existence of epistasis was observed in either one or both conditions by one or both types of scaling tests. The presence of complementary epistasis in cross P0 359 x Sonam and P0 1564 x Sarjoo-52 would make progress through selection procedures exploiting additive gene actions faster while existence of duplicate epistasis in cross NDR-359 x P0 1564 would have reverse impact. The non-additive gene effects in NDR-359 x P0 1564 for grain yield plant-1may also be utilized for facilitating development of pureline cultivars by involving population improvement methods. Our study concluded that for a large number of traits in six crosses, dominance gene effects and epistatic interactions were significant under drought and irrigated conditions implying that utilization of heterosis through hybrid varieties will act as a budding choice.

Genetic Parameters and QTLs for Total Phenolic Content and Yield of Wheat Mapping Population of CSDH Lines under Drought Stress.

A doubled haploid population of 94 lines from the Chinese Spring × SQ1 wheat cross (CSDH) was used to evaluate additive and epistatic gene action effects on total phenolic content, grain yield of the main stem, grain number per plant, thousand grain weight, and dry weight per plant at harvest based on phenotypic and genotypic observations of CSDH lines. These traits were evaluated under moderate and severe drought stress and compared with well-watered plants. Plants were grown in pots in an open-sided greenhouse. Genetic parameters, such as additive and epistatic effects, affecting total phenolic content, were estimated for eight year-by-drought combinations. Twenty-one markers showed a significant additive effect on total phenolic content in all eight year-by-drought combinations. These markers were located on chromosomes: 1A, 1B, 2A, 2B, 2D, 3A, 3B, 3D, 4A, and 4D. A region on 4AL with a stable QTL controlling the phenolic content, confirmed by various statistical methods is particularly noteworthy. In all years and treatments, three markers significantly linked to QTLs have been identified for both phenols and yield. Thirteen markers were coincident with candidate genes. Our results indicated the importance of both additive and epistatic gene effects on total phenolic content in eight year-by-drought combinations.

Genetic analysis of yield and quality traits through generation mean analysis in rice

The present investigation in rice (Oryza sativa L.) was undertaken to study the magnitude of gene action in two cross combinations for eleven yield and twelve quality traits deploying generation mean analysis following six parameter model for parents (P1 and P2), F1, F2, BC1 and BC2 generations during three crop seasons. The results of the scaling tests revealed that the additive-dominance model was inadequate for all of the characters evaluated in both the crosses suggested the existence of epistasis in the inheritance of these characters. Mean values of both the crosses revealed significant for most of the traits except effective bearing tillers per plant, SCMR, harvest index, kernel length and kernel L/B ratio in the cross BPT 5204 x IR 64. Major contribution of duplicate epistasis was revealed by the two crosses, for most of the characters. Few traits revealed complementary epistasis in both the crosses. The present study demonstrates the importance of additive, dominance and epistatic gene effects for the inheritance of almost all the yield as well as quality characters studied.

Estimation of additive and epistatic gene effects for phenotypic and biochemical traits in double hyploid lines of winter rape seed ,(Brassica napus L.)

In this paper 60 doubled haploid lines of winter oilseed rape (Brassica napus L.) were studied. Genetic parameters as additive and epistatic effects were estimated for 24 traits. The results indicate the importance of both these effects for number of branches per plant, number of siliques per plant, linoleic acid, total of glucosinolates, total of alkenyl glucosinolates, gluconapin, glucobrassicanapin, progoitryn, napoleiferin and indolyl in both years of this study. Statistically significant epistatic effect and non-significant additive effect for thousand seed weight means that this trait was determined by genes with small individual effects but strong gene by gene interaction effects. Confounding epistatic effects in models suggested that inheritance of this trait is complex and polygenic.

Generation mean analysis for yield and submergence tolerance in high yielding varieties of rice (Oryza sativa L.)

An investigation in rice (Oryza sativa L.) was carried out by utilizing two cosmopolitan rice varieties of Tamil Nadu namely ADT 43 and Improved White Ponni along with the donor submergence tolerance FR13A to reveal the genetics and gene action for submergence tolerance. The generation mean study was done by developing six generations viz., P1, P2, F1, F2, B1 and B2 for two cross combinations namely ADT 43 × FR 13A (Cross 1), IWP × FR 13A (Cross 2). Gene action studies for submergence tolerance through generation mean analyses revealed that all the yield and yield component traits under submergence condition were mostly influenced by dominance gene action, except for number of filled grains per panicle, total number of grains per panicle and spikelet fertility in cross 1. Regarding 1000 grain weight epistatic gene action was predominant in cross 1. In cross 2, dominant gene action alone was predominant for the trait number of productive tillers per plant whereas, the epistatic gene effects were predominant for the traits number of filled grains per panicle and total number of grains per panicle. The traits, days to flowering, plant height, number of tillers per plant, spikelet fertility, 1000 grain weight and single plant yield were controlled by additive, dominance followed by epistatic gene action. The generation mean analysis also revealed that number of filled grains per panicle, 1000 grain weight and single plant yield in cross 2 under submergence condition were much influenced by different types of gene action viz., additive, dominance and epistasis with complementary epistatic interaction. These crosses would be utilized for yield improvement through single plant selection in segregating generations. To obtain desirable segregants, the appropriate breeding method would be bi-parental mating or one or two cycles of recurrent selection followed by pedigree breeding will be effective and useful method to obtain expected improvement in rice under submergence tolerance.

Genetic studies in mungbean [Vigna radiata (L.) Wilczek

To study the genetics of seven agronomic and physiological characters (total dry matter (TDM), number of pods per plant, seed weight per plant, 100-seed weight, number of seeds per pod, pod length and root length density) which were correlated with yield, eight crosses of mungbean were made, and the agronomic and physiological characters were evaluated in the six basic generations (P1, P2, F1, F2, BC1 and BC2) of each cross. It was found that most characters including TDM, number of pods per plant, seed weight per plant and root length density showed additive, dominance and epistatic gene effects, except for 100-seed weight, number of seeds per pod and pod length. One hundred-seed weight and number of seeds per pod possessed only additive gene effects, while pod length was controlled by both additive and dominance gene effects. The duplicate epistasis revealed the presence of a large number of non-additive gene actions controlling TDM, number of pods per plant, seed weight per plant and root length density that may hinder the improvement of these characters, and confirmed that selection of these characters in later generations would be more feasible.

INHERITANCE OF SOME QUANTITATIVE CHARACTERS IN BREAD WHEAT (Triticum aestivum L.)

In this experiment, the means of the six populations (P1, P2, F1, F2, BC1 and BC2) of each of two bread wheat crosses; Mexipak × Acsad- 8 and Ipa- 99 × Attla were used to estimate gene effects, component of variance and heterosis for some quantitative traits viz: Plant height, days to heading, flag leaf area, spike length, spikes/plant, grains no./spike, biomass yield/plant, grain yield/plant and harvest index. These generations were produced during two growing seasons, 2009-2010 and 2010-2011. The generations were grown in a Randomized Complete Block Design with six replications at the Research Field of the College of Agriculture, Salahaddin University, Erbil, Iraq. Genetic analysis was performed using the joint scaling test based on three and six parameter models. The results revealed that inheritance of the traits could not be explained by additive-dominance model. Additive and dominance gene effects were significant for most traits in both crosses due to different origins of the parents. The values of (dominance × dominance) were greater than (additive × additive) and (additive × dominance) of most studied traits in both crosses in addition to greater values of dominance gene effect than the additive in most traits. It was suggested that selection all of them should be effective in advanced segregating generations due to epistatic gene effects. High narrow and broad sense heritability (0.94) was obtained for flag leaf area in Mexipak × Acsad- 8 cross, while high narrow sense heritability (0.86) and high broad sense heritability (0.98) were obtained for spike length and flag leaf area in Ipa- 99 × Attla, so the early generation testing and selection might be recommended for these traits. Heterosis was found to be positive for most traits in both crosses.