Estimates Of Genetic Components Research Articles

Estimation of genetic components and assessing heterosis association with molecular markers in half diallel derived rice hybrids developed with landraces of NE India

Combining ability and heterosis were estimated in 45 rice hybrids generated by mating 10 parents, comprising both land races and advance breeding lines, in half diallel fashion. Hayman’s graphical analysis showed that all the twelve morphological traits studied had significant positive dominance variance. Narrow sense heritability was high for Days to fifty percentage flowering, Plant height, Panicle length and Test weight (> 30 %), and low for Grain yield per plant. According to the VrWr graph, traits like GYPP, PL, PH, TN and plot yield showed partial dominance, whereas traits like Blast disease index showed overdominance. A significant improvement over check was observed for heterosis and the crosses Mynri x CAUS103, Joha x CAUS107, CAUS 126 x CAUS107 and CAUS103 x CP, exhibited significantly positive standard heterosis for GYPP (>80 %) and PY (>100 %). Genetic distance based on fourteen markers revealed significant positive association with mid parent and better parent heterosis for Spikelet’s per plant, Filled grains per plant, Harvest index, Grain yield per plant, Panicle number and Plot yield. Therefore, it is evident that crosses with larger genetic distance between the parents gave hybrids with higher heterosis. Keywords: Landraces, Hayman’s graphical analysis, Heterosis, Genetic distance

Estimation of genetic components, heterosis and combining ability of elite Pakistani wheat varieties for yield attributing traits and stripe rust response.

Wheat (Triticum aestivum L.) is a staple food and major source of dietary calories in Pakistan. Improving wheat varieties with higher grain yield and disease resistance is a prime objective. The knowledge of genetic behaviour of germplasm is key. To achieve this objective, elite wheat varieties were crossed in 4 by 3, line × tester design, and tested in 2019 in a triplicate yield trial to estimate genetic variance, general and specific combining ability, mid-parent heterosis and stripe rust (Puccinia striiformis L.). High grain 3358 kg·ha-1 was recorded in F1 hybrid (ZRG-79 × PAK-13). Analysis of variance (ANOVA) revealed significant genotypic variance in grain yield. Broad sense heritability (H2) was recorded in the range of 28 to 100 %. General combining ability (GCA) significant for grain yield in parents except FSD-08 and PS-05 was recorded, while specific combining ability (SCA) was recorded to be highly significant for grain yield only in two crosses (ZRG-79 × NR-09 and ZRG-79 × PAK-13). Mid-parent heterosis was estimated in the range of -28 to 62.6 %. Cross combinations ZRG-79 × PAK-13 depicted highly significant mid-parent heterosis (62.6 %). Highly significant correlation was observed among spike length, spikelets per spike, plant height and 1000-grain weight. Rust resistance index was recorded in the range of 0 to 8.5. These findings suggest exploitation of GCA for higher grain yield is important due to the presence of additive gene action and selection in the filial generations will be effective with improved rust resistance, while cross combinations ZRG-79 × PAK-13 high GCA are best suited for hybrid development.

A study of gene action for yield and quality traits of Basmati rice (Oryza sativa L.) following Hayman's graphical approach

The present study was conducted on 36 crosses obtained by carrying out a crossing program in nine Basmati rice genotypes following half-diallel mating design. Following, Hayman's graphical and numerical approach to comprehend the genetic system involved in the inheritance of traits, it was concluded that, out of 18 traits, only two traits viz., 100-grain weight, and aroma fulfilled the adequacy of additive-dominance model indicating absence of epistasis. Further, Vr/Wr graph was plotted and genetic components w ere estimated for these two traits only. By plotting Vr/Wr graph for 100-grain weight and aroma, partial dominance and over-dominance were observed in the inheritance, respectively. The ratio of KD/Kr implied influence of more of recessive alleles in inheritance of 100-grain weight among parents and dominant alleles for aroma genes among parents. Estimates of genetic components indicated the role of both additive and dominance effect in the inheritance of 100-grain weight and aroma. High heritability in narrow sense was observed for the traits.

Genetic Component and Vr-Wr Graphical Analysis in Blackgram [Vigna mungo (L.) Hepper

Background: To develop a new high yielding variety, it is important to generate utilitarian recombinants and devise an appropriate strategy for selection and advancement of those recombinants. Method: Keeping this in mind, genetic components of yield and its related traits were determined in nine genotypes of blackgram through half diallel analysis using Hayman’s numerical and graphical approach. Conclusion: The estimates of genetic components deduced the role of non-additive gene action in the inheritance of all traits. The Vr-Wr graphical analysis revealed that assumptions laid by Hayman for diallel analysis were seldom fulfilled. Epistatic effect was predominant in all traits except days to 75 per cent maturity. Unidirectional dominance was observed in days to 75 per cent maturity, pods per plants and seed yield per plant and crude protein content. One major gene group was found controlling all traits except days to 75 per cent maturity and branches per plant. These findings can be used by breeders to devise appropriate selection methodology for yield improvement in blackgram.

Genetic analysis of sugar yield and physiological traits in sugar beet under salinity stress conditions

Salinity is one of the most important constraints in sugar beet production in Asia. An understanding the genetic basis of sugar beet (Beta vulgaris) performance under salinity stress is crucial to gaining insight into salinity tolerance trajectories as well as to designing appropriate breeding strategies in saline stress conditions. In this study, a mating design (North Carolina Design II) was used to generate 116 hybrid combinations (29 × 4) from four male sterile and ten pollinator parents in sugar beet. Genetic variance components, combining ability, and heritability of 24 physiological and root yield and quality related traits were estimated by growing the hybrids and their 14 parents under normal and salinity stress conditions in the field. The results showed high genetic variation among the tested populations for most of traits. Estimates of genetic components for root, sugar and white sugar yield showed higher contribution of the dominance variance ( $$ \upsigma_{\text{D}}^{2} $$ ) than the additive variance ( $$ \upsigma_{\text{A}}^{2} $$ ) in both growing conditions, but with much greater magnitude of the $$ \upsigma_{\text{D}}^{2} $$ values observed for saline conditions. Narrow-sense heritability (Hn) was generally higher in stress environment for physiological traits compared to those of normal ones and the reverse held true for the yield traits. The results of general combining ability (GCA)for the yield traits showed a non-consistent trend across normal and stress environments. Both GCA and specific combining ability (SCA) were found to be important for the performance of individual hybrid combinations, and no clear relationship between GCA and SCA was found for these sugar beet genotypes. Given the higher impact of dominance variance and the lower narrow sense heritability of sugar yield in saline conditions compared to normal conditions, it can be concluded that hybrid breeding strategy should be more favored in saline environments than normal environments.

Estimation of Genetic Components and Heritability for Fruits Yield and Quality Characters in Tomato (Solanum Lycopersicom)

Six parental genotypes of tomato (Solanum Lycopersicom), i.e. Castel ruck (p1), Imperial (p2), Crystal (p3), Perso (p4), Pascal (p5) and Valcum valentime (p6) were crossed in a half diallel fashion to produce F1 in order to study some genetic components and ratios for some economic traits. The study consisted of twenty one genotypes; these genotypes were six inbred lines (parents) and fifteen F1 crosses. These twenty one genotypes were subjected to evaluation trial at Moshtohor village, Kalyobiya Governorate, Egypt during summer seasons of 2016 in a randomized complete block design with three replications. Data on yield and its components and fruit traits were recorded and subjected to statistical analysis to investigate Hayman's approach were used to study genetic components and heritability which control these traits. Data indicated that the additive component (D) was insignificant for average fruit weight, number of fruits and total yield per plant traits indicating the importance of non-additive effect in the inheritance of these traits. Meanwhile, the dominance genetic variations H1 and H2 were significant or highly significant for all studied fruits traits, showing the importance of dominance genetic effects in the inheritance of these traits. The average degree of dominance (H1/D) ½ showed over dominance for the average fruit weight, number of fruits and fruit yield per plant traits. The proportion of gene with positive and negative effects (H2/4H1) in the parents was lower than one quarter proportion, indicating unequal distribution between the positive and negative alleles among the parents. The ratio of dominant to recessive alleles (KD/KR) in the parents was more than (one), indicating that the six parents used in the present study carried more dominant than recessive allels. Heritability estimates in broad sense are very high for average fruit weight trait (100%), number of fruits (96%) and fruit yield per plant (92%), indicating the importance of genetic components of variation in the inheritance of these traits encouraging the usage of breeding programs to improve these traits. Meanwhile heritability estimates in narrow sense was low (2.7%, 1.4% and 0.7 %, respectively) clarifying the importance of non-additive genetic effects in the inheritance of these traits. These results indicate that a major of total phenotypic variances due to dominance and/or over-dominance and the environmental factor affects the inheritance of these traits. So it is of great importance to develop new hybrids in order to obtain maximum fruits number.

<b>Strategies to select soybean segregating populations with the goal of improving agronomic traits

The success of breeding programs depends on selection procedures and on the breeding methods adopted for selecting segregating populations. The objective of this study was to evaluate the efficiency of the Bulk method with selection in the F3 generation (BulkF3) compared to that of Bulk method as well as determine the most effective selection strategy in terms of genetic gain. Twenty segregating populations were selected by two methods. The 60 best families of each method were selected according to their average agronomic performance. An augmented block design was used. The following agronomic traits were evaluated: insertion height of first pod, plant height at maturity, number of branches and of pods per plant, 100-seed weight, and grain yield. For comparison of the methods, genetic component estimates, genetic gain and predicted breeding values were calculated using mixed models (REML and BLUP). The results showed the families obtained with the BulkF3 method were more productive, showed suitable plant height, a larger number of branches and pods, and higher 100-seed weight. The BulkF3 method was found to be an effective selection strategy for soybean improvement.

Estimates of Genetic Component of Variances and Genetic Ratios for Earliness and Yield Attributing Traits in Cucumber

Estimates of Genetic Component of Variances and Genetic Ratios for Earliness and Yield Attributing Traits in Cucumber

Estimates of genetic components and regression analysis for grain yield and various morphological traits in bread wheat (Triticum aestivum L.)

The present study was conducted to estimate the gentic components and regression analysis for grain yield and various morphological traits in bread wheat involving 10 parents and their 45 F1s (half diallel) during 2012- 13 and 2013-14. Significant additive (D) and dominance (H1) variance for the traits indicated that expression of these traits is control by both additive and dominance gene action. Average degree of dominance (H1/D)1/2 were more than unity for the traits (peduncle length, flag leaf area, productive tillers, biological yield, grain yield, harvest index) indicating the preponderance of over dominance gene action. The estimates of h2 were positive and significant for days to ear emergence, peduncle length, productive tillers, biological yield and grain yield indicated dominance of genetic components in F1s. Positive and significant values of F were estimated for days to ear emergence, days to 50% flowering, spike length, flag leaf area and grain yield in F1s indicating the preponderance of dominance and positive genes in the parents involved. The theoretical value (0.25) of (H2/4H1) for all the traits indicated asymmetrical distribution of positive and negative genes. The proportion of dominant and recessive alleles indicated presence of dominant alleles in the parents. The traits showing more than 30% narrow sanse heritability could be rewarding for further improvement in grain yield in bread wheat. Regression analysis indicated that the traits (days to ear emergence, days to 50% flowering, peduncle length, flag leaf area, productive tillers, harvest index, biological yield and grain yield) control by over dominance type of gene action. The parent RAJ 4246 contained maximum dominant genes for days to ear emergence and days to 50% flowering; HD 2733 for spike length and flag leaf area and HD 2824 for productive tillers, biological yield and grain yield used as donors in multiple traits breeding programme to develop high yielding wheat genotypes.

Genetic basis of variation for seedling traits in Gossypium hirsutum L.

A 6 × 6 complete diallel analysis was performed to study the inheritance of seedling traits in cotton. Significant differences among genotypes showed the genetic variation and formal analysis predicted the presence of both additive and non-additive genetic variation for inheritance of seedling traits. Further, the estimates of genetic components D, H1 and H2 confirmed the presence of both additive and non-additive genetic effects for all the characteristics. Dominant genes were responsible for the increase of seedling shoot length, root length, shoot weight and root weight. However, recessive genes were accountable for the increase of shoot root ratio by length and by weight. Seedling shoot length, root length and root weight can be improved through heterosis breeding. The magnitude of broad sense heritability was greater than narrow sense for all the six traits under study hence diminished the scope of selection in the early segregating generation therefore pedigree breeding method is suggested for the improvement of these traits. Key words: Additive dominance model, gene action, Gossypium hirsutum L,heritability, seedling traits

Fatores genéticos e ambientais da atividade física. Um estudo em famílias com três gerações

This study aims (1) to investigate the presence of familial aggregation in physical activity (PA) levels and sedentary behavior (SB) among members of three generations families and (2) to estimate the magnitude of additive genetic influences on PA and SB phenotypes. The sample consisted of 100 extended families covering three generations (n=1034), from the Lisbon area, Portugal. Phenotypes were assessed via the short version of the self-administered International Physical Activity Questionnaire (IPAQ-SF). Measured phenotypes: total physical activity (TPA); vigorous (VPA); moderate (MPA); walking; time spent in sitting time (ST), watching television (WT) and PA levels classification. Body mass index (BMI) was calculated. Exploratory family analysis in all phenotypes was conducted in PEDSTATS software. The genetic component (h2) and shared environmental effect were estimated using maximum likelihood implemented in the SOLAR software package. All graphs were done in HLM software. Sex, age, sex*age, age2, sex*age2 and BMI were used as covariates. Significant level was set at 0,05. Genetic component estimates (h2) were as follows: TPA h2=0,28±0,06 (p<0.0001); VPA h2=0,35±0,06 (p<0.0001); MPA h2=0,29±0,06 (p<0.0001); walking h2=0,40±0,06 (p<0.0001); ST h2=0,29±0,06 (p<0.0001); WT h2=0,15±0,06 (p<0.003) and determination of the level physical activity h2=0,35±0,14 (p<0.007). Shared environmental effect was not significant. These results showed a low-to-moderate genetic contribution, between 15% to 40% of the total variability, in the PA and SB phenotypes. The genetic factors have low to moderate influence in this sample. Non-shared environmental factors appear to have the major contribution in these phenotypes.

Sexual variation in heritability and genetic correlations of morphological traits in house sparrow (Passer domesticus)

Estimates of genetic components are important for our understanding of how individual characteristics are transferred between generations. We show that the level of heritability varies between 0.12 and 0.68 in six morphological traits in house sparrows (Passer domesticus L.) in northern Norway. Positive and negative genetic correlations were present among traits, suggesting evolutionary constraints on the evolution of some of these characters. A sexual difference in the amount of heritable genetic variation was found in tarsus length, wing length, bill depth and body condition index, with generally higher heritability in females. In addition, the structure of the genetic variance-covariance matrix for the traits differed between the sexes. Genetic correlations between males and females for the morphological traits were however large and not significantly different from one, indicating that sex-specific responses to selection will be influenced by intersexual differences in selection differentials. Despite this, some traits had heritability above 0.1 in females, even after conditioning on the additive genetic covariance between sexes and the additive genetic variances in males. Moreover, a meta-analysis indicated that higher heritability in females than in males may be common in birds. Thus, this indicates sexual differences in the genetic architecture of birds. Consequently, as in house sparrows, the evolutionary responses to selection will often be larger in females than males. Hence, our results suggest that sex-specific additive genetic variances and covariances, although ignored in most studies, should be included when making predictions of evolutionary changes from standard quantitative genetic models.

Inheritance of resistance in maize to the African stalk borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae)

The inheritance of resistance to the African stem borer, Busseola fusca, in maize was investigated by means of line x tester analyses in the F1 to F4 generations of crosses between 18 susceptible inbred lines and two resistant testers of common genetic background. Based on artificial infestation of plants followed by evaluation of leaf feeding damage, additive gene action was found to be significant for resistance, whereas dominance was nonsignificant in all cross combinations, using phenotypic assessment of gene expression in various generations. However, estimates of genetic components showed both additive and dominant gene action to be important. Significant additive x additive and dominance x dominance gene interactions were found, indicating non-allelic interaction and that resistance is controlled by several genes at different loci. Using a rating scale to test for absence of epistasis indicated one locus non-allelic interaction to be negligible, but did not exclude non-allelic interaction for two or more loci. Heritability in the broad sense was high, while the estimated narrow sense heritability was low, indicating non-additivity of gene effects. Estimates of combining ability showed greater SCA than GCA in most crosses, indicating that the inheritance depended both on the source of resistance and the susceptible inbred parent used in the particular combination. This suggests that each susceptible inbred line possesses one or more of the possible loci from the polygenic pool of resistant genes. Results confirmed that selection for resistance should not be initiated in the F2 generation but from the F3 and onwards, when the segregating variability should be reduced.

Estimation of Genetic Components in Popcorn Based on the Nested Design

The quantification of genetic components in a base population is essential for the definition of the best breeding strategy to maximize the genetic gains. To evaluate several agronomic traits such as grain yield (GY) and popping expansion (PE) in half-sib and full-sib families derived from an open pollinated popcorn population, this study used a nested design, in two contrasting environments in the Northern Fluminense region of Rio de Janeiro, Brazil. Results showed: a) high significance of male and female within male sources of variation for most traits studied; b) absence of genotype by environmental interaction for PE; c) overdominance for GY and additivity for PE; d) low narrow sense of heritability for GY as opposed to PE; e) intermediate family heritability mean for GY and high for PE; and f) high genetic gain estimates for both GY and PE provided by the full-sib recurrent selection. These results indicate the perspective of success for intrapopulation breeding methods in popcorn for popping expansion allowing the prediction of satisfactory genetic gain for the Northern Fluminense.

Genetic variance and covariance components related to intra- and interpopulation recurrent selection in maize (Zea mays L.)

New genetic variance and covariance components related to intra- and interpopulational recurrent selection methods have been theoretically developed by Souza Jr. (Rev. Bras. Genet. 16: 91-105, 1993) to explain the failure of these methods to concomitantly develop hybrid and per se populations. Intra- and interpopulation half-sib progenies of 100 genotypes were sampled from maize (Zea mays L.) populations BR-106 and BR-105 to estimate variance and covariance components and to compare the expected responses to reciprocal (RRS), intrapopulational (HSS), and modified (MRS) recurrent selection in interpopulation hybrid, populations per se, and to determine heterosis. Four sets of 100 progenies, two intra- and two interpopulational, were evaluated in partially balanced 10 x 10 lattices arranged in split-blocks with two replications in two years (1991/92 and 1992/93) and two locations in Piracicaba, SP. Data for ear weight, plant and ear height, and ear by plant height ratio were recorded. Populations and interpopulation crosses were high yielding and showed high breeding potential for production of hybrids from inbred lines. Mid parent and the highest parent heterosis were relatively high, but lower than values reported for these populations under other environmental conditions. Additive variance estimates of populations per se and interpopulation crosses confirmed the high potential of these materials. The magnitude of the variance estimates for the deviations from intra- and interpopulation additive effects (&lt;img src="http:/img/fbpe/gmb/v21n4/1918f1.jpg" alt="1918f1.jpg (1262 bytes)" align="middle"&gt; for BR-106 and &lt;img src="http:/img/fbpe/gmb/v21n4/1918f3.jpg" alt="1918f3.jpg (1259 bytes)" align="middle"&gt;for BR-105) and covariance between additive effects with these deviations (&lt;img src="http:/img/fbpe/gmb/v21n4/1918f2.jpg" alt="1918f2.jpg (2022 bytes)" align="middle"&gt; for BR-106 and &lt;img src="http:/img/fbpe/gmb/v21n4/1918f4.jpg" alt="1918f4.jpg (1995 bytes)" align="middle"&gt; for BR-105) indicated that these new components can significantly influence the effectiveness of breeding methods. Genetic component estimates for BR-105 had relatively small errors, with &lt;img src="http:/img/fbpe/gmb/v21n4/1918f4.jpg" alt="1918f4.jpg (1995 bytes)" align="middle"&gt; negative for all traits. Estimates of &lt;img src="http:/img/fbpe/gmb/v21n4/1918f1.jpg" alt="1918f1.jpg (1262 bytes)" align="middle"&gt;and &lt;img src="http:/img/fbpe/gmb/v21n4/1918f2.jpg" alt="1918f2.jpg (2022 bytes)" align="middle"&gt; had relatively larger errors for BR-106. The MRS method was more effective than the RRS and HSS methods in producing hybrids from inbred lines. The choice of a population tester for the MRS method based on population means per se may be incorrect. The additional use, when possible, of intra- and interpopulation additive genetic variances from each population would be more appropriate.

Maternal effects and generation mean analysis of seed-oil content in cotton (Gossypium hirsutum L.)

The nature of gene action and of maternal influence governing cottonseed oil attributes were determined with four lines, two each with high and low seed-oil percentage. For this purpose, P1, P2, F0, F1, F2 and alternative sets of BC1 and BC2 generations were analysed in six cross-combinations and their reciprocals. Marginal extents of heterosis for seed-oil percentage were noticeable in F1, with inbreeding depression in F2. Data from reciprocal backcrosses provided evidence in favour of maternal rather than cytoplasmic effects of seed-oil development. Relatively higher extents of heterosis, sizeable inbreeding depression and reciprocally unequal F2 averages were characteristic of the seed index trait, which often showed a reversal of effects from F1 to F2. Reverse reciprocal backcrosses exhibited some differences, including greater resemblance between the types, (A/B)A and (B/A)A, in addition to variable dose effects in seed index. Thus, the differences between F1 seed index values were not due to cytoplasmic influence. Positive heterotic effects for seed-oil index, especially among the backcrosses, ranged between 16.08% and 47.29% over midparent averages. Genetic component estimates from analysis of similar sets of crosses differing only in reciprocal backcrosses, and also from sets of reciprocal crosses between any two parental combinations, were inconsistent. Scaling tests detected presence of epistasis within and between a majority of cross-combinations. Despite reciprocal differences, additive gene effects for seed-oil percentage were significant in 7 out of 24 crosses, representing high x low, low x high and low x low seed-oil parents. Those were, however, accompanied by significant dominance effects of higher order. In crosses involving low seed-oil percentage parents SA1060 and SA229, all six components were detected significant, with opposite effects of dominance and dominance x dominance epistatic components. Significant additive components were also detected for seed index and seed-oil index in 7 and 5 out of 24 crosses, respectively. In the inheritance of seed index and seed-oil index, dominance effects were more important. Epistatic components of additive x additive, and to a lesser extent, those of dominant x dominant were found significant.

Joint analysis of triple test crosses of a single population with associated and dispersed inbred testers

If two pairs of pure breeding lines and their respective F1's are used as two sets of testers in triple test cross investigations of the same population, the data can be subjected to a combined orthogonal analysis of variance. Where one pair of pure breeding testers is relatively dispersed (usually the parents whose cross produced the population) and the other pair is relatively associated (usually extreme selections from the population), the orthogonal comparisons yield estimates of the additive genetic, dominance and epistatic components of variation and information about the genetical constitution of the testers. The theoretical expectations for the six principal orthogonal comparisons of the combined analysis are presented for the simple case which assumes no non-allelic interaction and a linkage equilibrium, and for more complex situations where one or both of these assumptions is relaxed. The combined analysis of two triple test crosses on 60 F∞, families derived from the cross of V2 and V12 of Nicotiana rustica, using V2, V12 and their F1 as one set of testers and two extreme F∞ families, D10 and D17 and their F1 as the other set, confirm earlier analyses of this cross. The estimates of the genetical components are intermediate in value between those of the separate, conventional triple test cross analyses but the standard errors of the dominance components are lower. In addition the combined analyses show that there have been major changes in the distribution of dominant alleles between the two sets of inbred testers as well as changes in the phases of alleles in the testers at loci that contribute to the epistatic variation. These changes are in the direction expected from the origins of the testers and their estimated coefficients of association/dispersion.

Variation in Some Plant and Seed Oil Characteristics of Meadowfoam

Meadowfoam (Limnanthes spp.), like jojoba (Simmondsia chinensis), promises to be a new agronomic substitute for sperm whale oil. Original bulk seed materials of four Limnanthes species from 35 collection sites were studied for interpopulational variation in fatty acid composition, oil content, and seed weight. Analyses of variance indicated significant interpopulational differences in the relative content of 22:1 and 22:2 fatty acids for the three species L. alba, L. floccosa, and L. douglasii. Differences among species for oil content, fatty acid composition, and seed weight were statistically as large as the estimates of interpopulation variances. A pilot study of heritability and interpopulational variation was carried out, using material from five collections, for oil content, component fatty acids, number of seeds per flower, flower number, branch number, plant height, and seed weight. Parentprogeny regression coefficients, calculated for the first four of these characters, indicated low heritability; likewise, the estimates of genetic component between vs. within families varied depending on the character and population involved. Correlations between several growth and reproductive characters suggested that yield components such as flower number, branching, and seed set per flower could be simultaneously improved by selection in the progeny of interpopulation hybrids.

Epistatic bias and gene action for protein content in green-gram (Phaseolus aureus Roxb.)

A study to ascertain the epistatic bias in the estimates of genetic components of variance and sensitivity of the test for epistasis based on the deviation of regression coefficient from unity was conducted. It indicated that the absence of deviation of regression of Wr to Vr from unity is not always a sure test of the absence of epistasis. Graphical, combining ability and variance component analyses suggested the importance of both additive and non-additive components of variance for protein content. The non-additive component of variance was constituted both by dominance and epistatic variance. Predominantly, the epistasis observed, was reinforcing degree of dominance yet, the existence of the one reducing degree of dominance has not been ruled out. High protein content appears to be controlled by dominant genes. Positive (dominant) and negative (recessive) genes were equally frequent and were randomly distributed among the parents. The improvement in this character is possible through accumulation of favourable dominant genes.

Genotype-Environment Interaction Concepts for Field Experimentation

A reference set of experiments based on sets of random environments available in time and space was characterized and used as a framework for considering genotype-environment interactions in quantitative genetic studies. Biases, introduced when data collected for y years at 1 sites were analyzed as a set of random environments, were evaluated. The ramifications involved primarily the magnitudes of the estimates for two intraclass correlations. Experimental estimates for the correlations were obtained from published genotype-environment studies conducted primarily in North Carolina. With the procedures presently used to select test sites, the sites and years had similar effects on relative genotypic responses, and one should be able to analyze associated environments as random without unduly biasing his estimates of genetic components.