Estimates Of Additive Variance Research Articles

Variability in a Silage Maize “Zea mays, L.” Base Population via Two Types of Families 3. Forage botanical composition and dry matter partitioning

The base population for the recent study which is a yellow seed synthetic variety of maize was provided by Dr. M. Abd El-Sattar Ahmed, professor of crop science, Crop Science Department, faculty of Agriculture, Egypt. Two types of families had formulated, as a step before selection for high yielding ability. Those were half-sib (H.S) families and the first generation of self-pollination (S1) families. Variability in the base population gene pool had estimated depending on vari-ance components of the families. Reduction in mean values associated with S1 families relative to half-sib families reached 0.182, 1.18, 0.98, 3.88, 2.75 and 5.72% for leaves percentage, stem percentage, ear percentage, grain percentage, cob per-centage and husk percentage, respectively. Genotypic variances among S1 families was larger in magnitude than the respec-tive value for half-sib families in each measured botanical composition and dry matter partitioning characters. Meanwhile, within family’s variance, (σ2f), environmental variances (σ2e) had reduced in S1 families relative to half-sib families in each measured character. Genotypic variation among half-sib and S1 families were less than 20% of the studied botanical compo-sition and dry matter partitioning characters mean values, except for cob percentage and husk percentage that had a genotyp-ic variation amount to 24% and 26%, respectively. The estimates of additive variance (δ2A) were positive for all studied botanical composition and dry matter partitioning characters. While, the estimates of dominance variance (δ2D) were nega-tive for all characters, the ratio of δ2A/δ2G indicated that additive genetic variance was more effective in controlling all stud-ied botanical composition and dry matter partitioning characters. Estimates of heritability were higher in magnitude when calculated from first selfing generation (S1) compared to half-sib families, for all studied characters. Stem percentage ex-pressed the least estimate heritability among all studied characters in each family type (0.798 and 0.414 for half-sib and S1 families, respectively). This might indicate the influence of environment in the expression of that character. Meanwhile husk percentage had highest genetic control expressed on heritability estimates from the two studied types of families.

English

The type of gene action conferring combined resistance to maize streak virus (MSV) and maize stripe virus (MStV) was investigated in a Quality Protein Maize (QPM) population, ART/98/SW6-OB. Full-sib and half-sib progenies generated using North Carolina Design I mating scheme were evaluated in 2015 and 2016 in two locations endemic to the viral diseases in Nigeria. Serological study was also conducted on the progenies to validate the disease scores on the field. Significant mean square of genotypes was observed for MSV severity, MStV incidence and severity, plant height and days to flowering, while mean square of environment by females in males’ interaction was significant for grain yield and MSV incidence. Estimates of additive variances were larger than dominance variance for grain yield and MSV severity with moderate to high narrow-sense heritability estimates. This indicates that there is adequate genetic variability for improving grain yield and resistance to MSV in the maize population. The mean titre values of MSV and MStV for the progenies were significantly higher than the healthy control. MSV and MStV incidence were negatively correlated to days to 50% silking. Titre values were negatively correlated with grain yield but positively correlated with MSV and MStV incidence. Recurrent selection method that capitalizes on both additive and dominance variances would be effective in improving the population for grain yield and resistance to MSV and MStV diseases.   Key words: Correlation, gene action, maize streak virus, maize stripe virus, resistance, North Carolina design.

Genetic analysis for beta glucan, grain protein and other important traits in oats (Avena sativaL.)

The parents and 45 F1 crosses (excluding reciprocals) in oats (Avena sativa L.) were analyzed genetically to generate information on combining ability, nature and magnitude of gene effects for beta-glucan, grain protein and physiological traits. The estimates of additive variance were higher in magnitude than their corresponding dominance genetic variance indicating the role of additive gene action for grain protein content and beta-glucan and for physiological traits like chlorophyll content, leaf area index and grain yield per plant that showed non additive gene action. Four parents SKO-207, SKO-208, SKO-209 and SKO-212 were found to be good combiners for all traits studied. Twelve cross combinations viz., SKO-204 X SKO-207, SKO-204 X SKO-208, SKO-205 X SKO-208, SKO-205 X SKO-212, SABZAR X SKO-208, SKO-207 X SKO-208, SKO-207 X SKO-209, SKO-208 X SKO-209, SKO-208 X SKO-212, SKO-209 X SKO-212, SKO-211 X SKO-212 and SKO-211 X SKO-213 exhibited desirable positive SCA effect for physiological traits, grain quality and yield.

Combining Ability Studies for Yield and Yield Attributing Traits in Sweet Pepper (Capsicum annuumL.)

Ten diverse lines of sweet pepper were crossed in diallel manner to generate forty five crosses. The crosses and parents were evaluated in randomized complete block design during Kharif, 2010 at three different locations. The observations were recorded on various yield and yield attributing traits. Analysis of variance for combining ability revealed that variances due to GCA and SCA were significant for all the traits suggesting the importance of both types of variances in the inheritance of the traits. GCA and SCA also interacted significantly with the environments. The estimates of dominance variance were higher in magnitude than corresponding estimates of additive variance indicating the preponderance of non-additive gene action. None of the parents exhibited desirable gca effects for all the traits simultaneously. However, overall ranking of genotypes revealed that the parents SP-82, SP-640 and California Wonder exhibited significant desirable GCA effects for most of the traits. None of the crosses exhibited significant desirable SCA effects for all the traits simultaneously. However, the crosses SP-29 x SP-640, California Wonder x SP-82 and SP-82 x SP-614 were found to be desirable for most of the traits.

Genetic effects of combining ability on forage quality traits and forage yield in diallel crosses of oats (Avena sativaL.)

Studies in oats (Avena sativa L.) were carried out to generate information on combining ability (general and specific), nature and magnitude of gene effects and heterosis for forage quality and yield. The experimental material comprised of 10 diverse parents and 45 F1 crosses (excluding reciprocals) generated through a 10 x 10 diallel mating design. Significant interaction between combining ability effects were observed for all the quality traits and yield. The estimates of additive variance were higher in magnitude than their corresponding dominance variance estimates indicating the role of additive gene action, except green forage yield and dry matter yield. The parent SKO-213 had highly significant and desirable GCA effects for crude protein content, SKO-210 for neutral detergent fibre, SKO-204 for acid detergent fibre, SKO-208 for crude fibre parent, SKO-207 for ash content and SKO-212 for both green forage and dry matter yields. Cross combinations viz., SKO-212 x SKO-213, SKO-204 x SKO-211, SKO-205 x Sabzaar, Sabzaar x SKO-212 and SKO-205 x SKO-211 exhibited high and desirable sca and heterobeltiosis effects simultaneously for all the quality traits, green forage yield and dry matter yield ha−1.

Predictive ability and covariance parameters of dynamic linear models for analysis of longitudinal traits1

A set of analyses using a multiple-trait model (model 1) and dynamic models for the evaluation of beef cattle growth is presented. All models contained additive direct and maternal environmental effects, as well as contemporary groups as nuisance parameters. The predictive ability of models at different parts of the growth trajectory was compared. Body weight records of 6,856 Nelore animals taken at 6 different ages (birth to 540 d) were used. Different models embedding a Kalman filter (KF) into a mixed model representation were fitted. Model 2 assumed that additive, maternal, and residual effects changed over time according to a linear autoregressive process. Model 3 was similar to model 2, but all regression coefficients were set to 1. In model 4, KF was applied only to direct genetic and maternal environmental effects. A leave-one-out cross-validation check was used to assess the predictive ability of models. Estimates of additive variance were similar in the analysis with models 1, 3, and 4 for all ages. Posterior means of maternal components increased slightly after birth and decreased after 135 d of age. Posterior means of additive rates of change were close to 1 at almost all time points, irrespective of the model. The posterior means of residual rates of change, which varied from 0.096 to 0.529, did not support the restrictions that regression coefficients were equal to 1 imposed by model 3. Estimates of additive and maternal correlations obtained with dynamic models were larger than those from a multivariate model. Model 3 produced different phenotypic correlations. Models 2 and 4 had better predictive ability than the multivariate specification. Model 3 predicted the data very poorly, and errors increased markedly with age. The KF can be a useful tool for structuring (co)variance matrices without reducing dimensionality. This model provided accurate predictions and plausible estimates of (co)variance components. Moreover, KF is a flexible specification, because a multivariate structure can be used for some random effects, whereas a dynamic feature can be incorporated for others.

Genetic and environmental relationship among udder conformation traits and mastitis incidence in Holstein Friesian into two different environments

Abstract. Type-performance of udder of Holstein-Friesian was analyzed using multi-trait animal model in two different environments (Hungary and Egypt). Udder traits were: udder height and depth. Teat traits were teat length, attachment and placement. Multi-trait animal model was used to compute estimates of additive variance and covariance components. 2507 records of 549 cows and 6011 records of 2018 cows were collected from Egypt and Hungary respectively. Heritability estimates of udder and teat characteristics ranged from 0.35 to 0.45 and from 0.32 to 0.59 in Hungarian and Egyptian cows, respectively. Heritability estimates of udder traits in both environments were higher than the corresponding estimates for teat traits. Udder characteristics of Egyptian Holstein-Friesian (EHF) had inheritance power higher than for Hungarian Holstein-Friesian (HHF). Mastitis was moderately correlated with udder height and teat traits in each environment. Additive genetic variance and heritability of the most studied traits increased with the advancing order of lactation in each environment. Heritabilities of mastitis were low. Sire and dam variance components of all studied traits were higher in EHF than HHF herds. Mastitis was strongly correlated negatively with udder depth of EHF than HHF. The genetic analysis results of the present study, indicate that udder characteristics should be taken into consideration during planning of selection strategies for improving dairy cattle performance. Enhancing management levels of Egyptian environmental conditions is very essential for improving general performance of the most exotic dairy cattle breeds. EHF has great chances for genetic improvement to mastitis resistance through selection, based on udder descriptive performance.

The quantitative genetics of maximal and basal rates of oxygen consumption in mice.

A positive genetic correlation between basal metabolic rate (BMR) and maximal (VO(2)max) rate of oxygen consumption is a key assumption of the aerobic capacity model for the evolution of endothermy. We estimated the genetic (V(A), additive, and V(D), dominance), prenatal (V(N)), and postnatal common environmental (V(C)) contributions to individual differences in metabolic rates and body mass for a genetically heterogeneous laboratory strain of house mice (Mus domesticus). Our breeding design did not allow the simultaneous estimation of V(D) and V(N). Regardless of whether V(D) or V(N) was assumed, estimates of V(A) were negative under the full models. Hence, we fitted reduced models (e.g., V(A) + V(N) + V(E) or V(A) + V(E)) and obtained new variance estimates. For reduced models, narrow-sense heritability (h(2)(N)) for BMR was <0.1, but estimates of h(2)(N) for VO(2)max were higher. When estimated with the V(A) + V(E) model, the additive genetic covariance between VO(2)max and BMR was positive and statistically different from zero. This result offers tentative support for the aerobic capacity model for the evolution of vertebrate energetics. However, constraints imposed on the genetic model may cause our estimates of additive variance and covariance to be biased, so our results should be interpreted with caution and tested via selection experiments.

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.

Linkage disequilibrium in crosses between Illinois maize strains divergently selected for protein percentage

The objectives of this study were two fold: (1) to determine whether divergent selection for kernel protein concentration, which produced the Illinois high protein (IHP), Illinois low protein (ILP), reverse low protein (RLP), and reverse high protein (RHP) maize (Zea mays L.) strains, had generated coupling-phase linkages among genes controlling protein concentration or other traits and (2) to measure the effectiveness of random mating in reducing linkage disequilibrium in segregating generations from crosses between the strains. To achieve these objectives, design III progenies from the F2 and F6 (produced by random mating the F2) from the crosses of IHP × ILP, IHP × RHP, ILP × RLP, and RHP × RLP were evaluated. Estimates of additive variance for percent protein in the crosses of IHP × ILP and ILP × RLP were significantly less in the F6 than in the F2 indicating the presence of coupling-phase linkages in the parents and their breakup by random mating. In addition, a significant reduction in dominance variance for grain yield from the F2 to the F6 in IHP × ILP suggested the presence of repulsion-phase linkages. No other evidence of coupling or repulsion-phase linkages was found for any of the traits measured. These results demonstrate the effectiveness of long-term divergent selection in the development of coupling-phase linkages and of random mating to dissipate linkage disequilibrium.

Estimation of genetic variance and allied parameters through biparental mating in opium poppy (Papaver somniferum L.)

Genetic variances and allied genetic parameters were estimated for eight economic traits through biparental mating designs in two populations: (i) a local land race, and (ii) a segregating F2 population of Indian opium poppy. Estimates of additive variance were larger than the dominance variances (o2A &gt; o2D) or environmental variance (+-R &gt; n�2) for the majority of the eight traits examined. Narrow sense heritability (h2NS) estimates were high (60-89%) for five traits, moderate (28.3%) for peduncle length and low (&lt; 13%) for capsule index and morphine content in the local land race, and high (57-93%) for all the eight characters in the F2 population. Average degree of dominance in the local population leaned heavily towards overdominance (G &gt; 1 .O) for six charcters (four in negative and two in positive directions) and towards partial dominance (G &lt; 1.0) for the remaining two traits: latex yield and flowering time (both in negative direction). Accordingly, combination breeding for latex yield and flowering duration, (F1) hybrid breeding for seed yield, morphine content and capsule number and/or population breeding for other traits, were suggested for rapid genetic improvement of opium poppy.

Genetic variance of six agronomic characters in three lentil (Lens culinaris Medic) crosses

Three lentil (Lens culinaris Medic) crosses (cross 1 = ‘Chilean’ × PI 297784; cross 2 = ‘Tekoa’ × PI 212611; cross 3 = ‘Precoz’ × PI 212611) were advanced in a hierarchal design from the F2 generation to the F5 generation and tested in replicated field experiments. The purpose was to estimate the genotypic variances and covariances for several characters and to partition these into components due to additive, dominance, and additive × additive variances. Additive genetic variance was the major component of variance in cross 2 for all characters, except plant height and seed weight. Unexpectedly, estimates of dominance variance appeared to be high in crosses 1 and 3. Estimates of the additive × additive component seemed very small in all three populations. The dominance variance component estimates were consistently high for plant height in the three crosses and for seed weight in crosses 2 and 3. Where parental means were close, additive variance estimates were often low and in many cases negative. The unexpected high ratio of dominance variance to additive variance indicated that dominance variance was important in the crosses we studied.

INHERITANCE OF DRY MATTER YIELD IN A HETEROZYGOUS POPULATION OF ALFALFA

Additive and digenic variances for dry matter yield were estimated from a population of F1 lines of alfalfa (Medicago sativa L.). The F1 lines and their polycross (PX) progenies were both evaluated over three harvests in a simulated sward in a growth room. From the analyses of variance, the genetic variances of the F1 and PX lines were estimated and the covariance between the F1 and PX performance calculated for dry matter yield. Correlations between relatives were used to partition these variances into additive and digenic effects. Narrow-sense heritabilities and the expected response to selection were estimated for the F1 population and broad-sense heritabilities were calculated from the F1 and PX trials. The pooled estimates of additive variance were significantly greater than zero for the second harvest and total yield while all estimates of digenic variance were nonsignificant. This indicated that the genetic variance for dry matter yield was mainly additive. The expected response to selection for total dry matter yield, if the top 10% of the F1 lines were recombined, was 23% of the F1 population mean. Based on these results, it was concluded that selection gains for yield could be made in this population of alfalfa.

Variability and Selection Advance for Photosynthesis in Iowa Stiff Stalk Synthetic Maize Population1

Photosynthesis is a primary trait influencing yield potential, and it should be improved in a yield‐potential selection program. Information concerning the genotypic variability and inheritance of photosynthetic efficiency in maize (Zea mays L.) must be obtained before a yield‐potential selection program is initiated.We used CO2‐exchange rate (CER) of sections from excised leaves to estimate photosynthetic efficiency of 64 random inbred fines of maize derived from Iowa Stiff Stalk Synthetic (BSSS). Our study was conducted for years at one location. Measurements of CER taken during vegetative growth (CER 1) and during grain filling (CER 2) were used to estimate genotypic variances and heritabilities and to calculate selection advances for these two stages of plant development. We also evaluated the possibility of using specific leaf weight and leaf thickness as index traits for CER selection.Results showed that estimates of additive variance were 1.7 and 4.9 times larger than estimates of genotype ✕ environment variance at CER 1 and CER 2, respectively. Narrow‐sense heritabilities were 0.58 for CER l and 0.80 for CER 2, and realized heritability values were 0.72 (CER 1) and 0.66 (CER 2). A high genotypic correlation between CER at CER 1 and CER 2 indicated selection at either developmental stage would produce nearly identical results. Actual selection advances (15% selection intensity) represented increases of 14 and 22% above population means for CER 1 and CER 2, respectively. Our data suggested that measurement of two replications of four plants/plot grown in two environments would provide most efficient selection advance for inbreds. We concluded that selection for improved CER in BSSS would be possible and that selection must be for CER per se.

A Quantitative Genetic Study of Verticillium Wilt Resistance Among Selected Lines of Upland Cotton1

A quantitative genetic study of the inheritance of resistance to verticillium wilt (Verticillium albo‐atrum Reinke and Berth.) was conducted among 10 selected lines of upland cotton (Gossypium hirsutum L.) utilizing the Jinks‐Hayman diallel analysis. Parents and F1's were studied in 1968 and 1969 at two locations in Oklahoma with the inclusion of F2 progenies in the second year.General tests of the diallel assumptions revealed a partial noncompliance with those assumptions in this material. Epistasis did not appear to be a complicating factor herein, but significant genotype by environment interactions were found among parents from year to year for their additive and dominance components of variation. A significant portion of the dominance interactions could not be attributed to either years or locations.All estimates of environmental variance and of additive genetic variance were significant, as were most estimates of dominance genetic variance. With one exception, estimates of additive variance were larger than the other parameters estimated in the same test. Wilt resistance displayed partial dominance except in one environment where overdominance was found to occur. Direction of dominance was toward greater susceptibility. The frequency of negative versus positive alleles in the parents was likely unequal and biased towards greater susceptibility. Narrow‐sense heritability estimates suggested that rapid genetic advances through selection could be made in most environments.