Relative Selection Efficiency Research Articles

Selection index for enhanced yield in rice genotypes

Plant breeding heavily relies on artificial selection to enhance grain yield through various contributing traits. The challenge in selecting complex quantitative traits, such as rice grain yield, lies in low heritability and a significant influence of environmental factors. This study involved 42 rice genotypes with the aim of identifying yield-contributing traits and establishing simultaneous selection models based on discriminant functions. The anticipated genetic gain for grain yield, when all the studied traits were considered in simultaneous selection, was notably higher (445.69%) compared to selecting grain yield alone (13.35%). The discriminant function comprised five traits: plant height (X1), number of filled grains per panicle (X4), number of grains per panicle (X5), seedling vigour index (X6), and grain yield per plant (X7). This combination exhibited a substantial genetic advance of 435.87% and a remarkable relative efficiency of 3264.05%. The relative efficiency of selection, considering grain yield alone, was set at 100%. However, when six ((X1, X3, X4, X5, X6, and X7) and seven traits were simultaneously considered, the efficiency increased to 3044.338 and 3337.606, respectively. Based on the ideal discriminant function, MTU3626 emerged as the best genotype with the highest selection score of 1706.046, followed by SM227 (1669.16) and NDP3 (1555.33). Conversely, MTU1010 ranked last with a selection score of 765.076.

Relative Efficiency of Selection for Yield and Some Related Characters in Some Populations of Grain Sorghum Sorghum bicolor L. Moench)

Relative Efficiency of Selection for Yield and Some Related Characters in Some Populations of Grain Sorghum Sorghum bicolor L. Moench)

Participatory Plant Breeding to develop biofortified upland rice for marginal environments

Abstract In the Highlands of Madagascar, where rice is the main staple food, explosive demographic growth has driven the need for the development of upland rice. In that context, a Participatory Plant Breeding (PPB) program conducted by the FOFIFA-Cirad partnership, aims to develop upland rice varieties adapted to farmers’ needs, with superior agronomic performances, and with high grain zinc concentration. In the area, where ferralitic soils with N and P deficiencies prevail, limited fertilizer usage persists due to elevated costs, and upland rice varieties must adapt to these low fertility environments. Thus, this paper aims to identify the adequate selection conditions and methods that allow combining the above-mentioned criteria for selection. So, 56 rice breeding lines, including high-zinc genotypes, were evaluated in field trials with contrasting fertility conditions. A relative selection efficiency analysis demonstrated that selection for yield should be done in moderate fertility environments, while selection for grain zinc concentration could be done across a diverse range of conditions. Through participatory evaluations, we identified that, for this case, grain appreciation was the most important character for deciding whether to select a line, followed by productivity and earliness. We also noted that farmers were more willing to accept a variety if it had higher grain zinc concentration. Finally, we proposed a selection index that combines agronomic, farmers’ and nutritional criteria, with the purpose of selecting lines that fulfill the expectations on these areas. Overall, this paper proposes an adapted methodology for the combination of PPB and biofortification in marginal environments.

Genetic parameters for growth and morphological traits of the Pacific white shrimp Penaeus vannamei from a selective breeding programme in the industrial sector of Ecuador

This study aimed to estimate the genetic parameters of growth-related traits (weight and length), morphological traits (cephalothorax, abdomen, length, height, segment width and volume), and the correlated response of weight traits via the selection for morphological traits to evaluate the relative efficiency of indirect selection in P. vannamei from a selective breeding growth programme, PMG-BIOGEMAR®, under industrial production conditions in Ecuador. A total of 595 shrimps from 89 full-sibling families were reared under an extensive culturing system (estuaries) (PRODUMAR, Duran, Ecuador), and were evaluated for genetic parameters at harvest size. The heritability of growth traits was moderate-medium (0.25–0.34), whereas it was quite variable for morphological traits (0.01–0.77). Among the morphological traits, Sixth Segment Width (SW6) (0.77) and Sixth Segment Volume (SV6) (0.35) had medium-high heritability, and genetic correlations between almost all morphological and growth traits were high and positive, except those corresponding to the fourth segment. According to these genetic parameters, SW6 and SV6 as the correlated response to weight are 9.7% and 5.8%, respectively, being more efficient than direct selection for weight. Thus, the sixth segment should be considered an indirect selection criterion for growth in future breeding programmes as it is a precise, non-invasive, and low-cost morphological trait for growth improvement in the industrial sector.

Estimates of genetic and phenotypic parameters for feeding behaviour and feed efficiency-related traits in Nelore cattle.

The objective of this study was to obtain (co)variance components, heritability, and genetic and phenotypic correlation estimates for feed efficiency and feed behaviour-related indicator traits. Further, it aimed to predict the direct and correlated responses for feed efficiency traits when selection was applied for feeding behaviour-related traits in Nelore cattle. Phenotypic records (n=4840) from 125 feed efficiency tests (RFI: Residual feed intake and DMI: Dry matter intake) carried out between 2011 and 2018 were considered in this study. Animals belonged to five farms located in two Brazilian geographical regions (Midwest and Southeast). Animals under similar management and environmental conditions in the feedlot were evaluated when they attained an average of 13.5± 4.15 months of age. Feed behaviour-related traits were also obtained, including meal criteria (MC), meal frequency (MF), average meal duration (AMD), meal duration (MD), average consumption per meal (ACM), and consumption rate (CR) through the GrowSafe System® electronic bunk system. The contemporary groups for all traits were composed of farm, management group, feed efficiency test, sex, and birth year. The (co)variance components were estimated using the restricted maximum likelihood method considering a multi-trait (n=8) animal model. The heritability estimates for RFI (0.23± 0.02), DMI (0.31± 0.02), MF (0.65± 0.02), AMD (0.29± 0.02), ACM (0.24± 0.02), MD (0.41± 0.02), MC (0.48± 0.02), and CR (0.42± 0.02) were moderate to high. The highest genetic correlation was obtained between CR and MD (-0.91 ± 0.04), MD and AMD (0.73± 0.03), CR and AMD (-0.68± 0.04), and RFI and DMI (0.81± 0.02). The highest phenotypic correlation was between ACM and AMD (0.76 ± 0.02), DMI and MD (0.77± 0.02), and DMI and RFI (0.77± 0.02). Genetic improvement for feed efficiency and feeding behaviour-related traits is feasible and the results obtained herein provided valuable information regarding the genetic background of Nelore feeding behaviour-related traits. The genetic association between feeding behaviour and feed efficiency-related traits suggested that animals spending less time feeding at a low feeding rate also had lower DMI and higher feed efficiency (RFI), and likely had lower energy maintenance requirements. The relative efficiency of selection showed that feeding behaviour-related traits were not adequate indicator traits to improve RFI and DMI. The DMI might be an effective selection criterion to improve RFI and reduce the herd's maintenance requirements.

Use of different selection indices for improving the genetic gain in maize (Zea mays L.)

Plant breeding relies heavily on artificial selection for improving grain yield through various yield contributing traits. The selection of complex quantitative traits like maize grain yield is difficult due to less heritability and a greater influence of the environment. The present study was made using 25 maize inbred lines aimed at identifying yield-attributing traits and identifying simultaneous selection models based on discriminant functions. The expected genetic gain for grain yield when all the studied traits were included in simultaneous selection was higher (51.86) than that of selecting grain yield alone (33.96). There were four traits that made up the ideal discriminant function: grain yield, kernels per row, 100-grain weight and cob length which had 49.57 percent relative efficiency and 155.29 percent genetic advance. The relative efficiency of selection considering grain yield alone was at 106.38%, but when five (X1, X2, X3, X5, and X6) and six traits were simultaneously considered the efficiency increased to 160.37 and 162.47%. Based on the ideal discriminant function among the genotypes G17 was selected as the best inbred line with the highest selection score of 66.57 followed by G20 (65.19) and G22 (65.01). Whereas, G23 was the last with 17.05 selection score

Selection indices for grain yield improvement in durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.

The plant breeder has certain desired plant characteristics in his mind while selecting for particular genotypes and for this he/she applies various weight to different traits for arriving at decisions. This suggests the use of a selection index that gives proper weight to each of the two or more characters to be considered. Among forty genotypes of durum wheat thirty-one selection indices, involving grain yield per plant and four yield contributing components, were constructed using the discriminant function technique. The superiority of selection based on index increases with an increase in the number of characters under selection. The selection index constructed based on five characters viz., grain yield per plant, days to maturity, plant height, biological yield per plant and harvest index exhibited maximum relative efficiency and selection efficiency. The plant breeder might be interested in maximum genetic gain with minimum number of characters. The maximum relative efficiency per character was observed in selection index comprised of days to maturity and plant height (X3 + X4) followed by plant height and biological yield per plant (X3 + X4 ).

Heritability and genetic correlations between marbling in longissimus dorsi muscle and conventional economic traits in Nellore beef cattle

In Nellore beef cattle, studies addressing genetic correlations between ultrasound marbling content and other economically important traits are still incipient. Therefore, this work aimed to estimate heritability and genetic correlations between ultrasound marbling content in the longissimus dorsi muscle (MARB) and growth, reproductive, feed efficiency, and carcass-related traits in a Nellore beef cattle population from Brazil. Phenotypic records of 614,395 Nellore animals were used and included adjusted weight at 210 (W210) and 450 (W450) days of age, adult cow weight (AW), early heifer pregnancy (EH), stayability (STAY), adjusted scrotal circumference at 365days of age (SC365), ribeye area (REA), subcutaneous backfat thickness (BF), rump fat thickness (RF), and marbling (MARB). The genetic parameters for all traits but EH and STAY were estimated considering a linear animal model, whereas for those two nonlinear traits, a threshold animal model was used. The direct and correlated response to selection for MARB versus the other traits, and the relative efficiency of selection, were also calculated. The heritability estimate for MARB was 0.31 and for the other conventional evaluated traits was low to moderate, with values ranging from 0.14 to 0.41. The genetic correlations between MARB and growth, reproductive, feed efficiency, and carcass-related trait were very low, with values close to zero, with similar correlated responses. The MARB displayed adequate genetic variability to respond to selection and crossbreeding programs looking forward to higher meat quality and differential market standards for the Nellore beef. The selection for growth, reproductive, feed efficiency, and carcass-related traits would not affect MARB in Nellore beef cattle and vice versa. Therefore, this trait should be included as a selection criterion in the Nellore breeding program.

Genetic Variation in Drought-Tolerance Traits and Their Relationships to Growth in Pinus radiata D. Don Under Water Stress.

The selection of drought-tolerant genotypes is globally recognized as an effective strategy to maintain the growth and survival of commercial tree species exposed to future drought periods. New genomic selection tools that reduce the time of progeny trials are required to substitute traditional tree breeding programs. We investigated the genetic variation of water stress tolerance in New Zealand-grown Pinus radiata D. Don using 622 commercially-used genotypes from 63 families. We used quantitative pedigree-based (Genomic Best Linear Unbiased Prediction or ABLUP) and genomic-based (Genomic Best Linear Unbiased Prediction or GBLUP) approaches to examine the heritability estimates associated with water stress tolerance in P. radiata. Tree seedling growth traits, foliar carbon isotope composition (δ13C), and dark-adapted chlorophyll fluorescence (Y) were monitored before, during and after 10 months of water stress. Height growth showed a constant and moderate heritability level, while the heritability estimate for diameter growth and δ13C decreased with water stress. In contrast, chlorophyll fluorescence exhibited low heritability after 5 and 10 months of water stress. The GBLUP approach provided less breeding value accuracy than ABLUP, however, the relative selection efficiency of GBLUP was greater compared with ABLUP selection techniques. Although there was no significant relationship directly between δ13C and Y, the genetic correlations were significant and stronger for GBLUP. The positive genetic correlations between δ13C and tree biomass traits under water stress indicated that intraspecific variation in δ13C was likely driven by differences in the genotype’s photosynthetic capacity. The results show that foliar δ13C can predict P. radiata genotype tolerance to water stress using ABLUP and GBLUP approaches and that such approaches can provide a faster screening and selection of drought-tolerant genotypes for forestry breeding programs.

Genetic associations between growth traits and age at first calving in Guzera cattle using random regression models

The aim of this study was to estimate genetic associations between body weight (BW), scrotal circumference (SC), and age at first calving (AFC) in Guzera cattle using random regression models. The analyses used 159,366 and 23,780 records of BW and SC obtained between 335 and 724 days of age and divided into classes at intervals of 10 days, as well as 63,596 records of AFC. A multitrait animal model via Gibbs sampling was adopted that included random direct additive genetic, permanent environmental (only for BW and SC), and residual effects. The fixed effects considered were the contemporary group, age of cow at calving (linear and quadratic effect), and the fixed curve to model the average trend of the population on the age classes of the animals. For BW and SC, four models were compared using the deviance information criterion, with Legendre polynomials ranging from one to four coefficients (intercept, linear, quadratic, and cubic) for additive genetic and permanent environmental effects. The model with three coefficients (quadratic) was considered the most appropriate to describe the (co)variance structure of the traits analyzed. The mean heritability estimates ranged from 0.17 to 0.31 for BW and from 0.19 to 0.28 for SC across age classes. The mean heritability for AFC was 0.07. The genetic correlations between BW and SC across age classes were always positive and favorable, ranging from 0.33 to 0.39. These findings indicate that selection for higher BW should result in animals with greater SC. The genetic correlations between BW at different ages and AFC ranged from -0.56 to -0.38, while those between SC at different ages and AFC ranged from -0.55 to 0.08. Except for some genetic correlations close to zero and positive between SC close to 365 days of age and AFC, in general the results showed that the selection for either higher BW or greater SC should result in a reduction of AFC in Guzera cattle. Calculation of the relative selection efficiency indicated a greater correlated response in AFC by selection for SC, especially after 634 days of age, compared to direct selection for AFC.

Multi-trait animal model based estimation of direct and correlated responses in Frieswal cattle

The study was undertaken to estimate the genetic parameters, direct and correlated responses for the test day and lactation milk yield in Frieswal cattle. Data on 9,955 daily milk yield records of 973 Frieswal cows calved during 2005 to 2014 at Ambala and Meerut dairy farms were utilized. The variance components, heritability estimates, genetic and phenotypic correlations for all the 11 traits were estimated simultaneously by fitting multi-trait animal model using the Wombat program of Meyer (2006) with contemporary groups as fixed effect, the additive genetic random effects, linear and quadratic regressions of covariate age at first calving and linear regression of covariate first lactation length. The expected genetic gain (DG), correlated response (CR) in cumulative 305-day yield and vice versa and the relative efficiency (RE %) of selection based on different test day yields were estimated. The results revealed lower additive genetic variance and heritability estimates for different test days and cumulative 305-day yield. The genetic correlations between the test days up to 225 and cumulative 305-days were higher which indicated the positive relationship between these traits. The higher correlated responses in cumulative 305- day yield estimated through the selection for TD135, TD165 and TD45, in that order indicated that early selection of sires using test day records would be efficient in genetic improvement for lactational milk yield in Frieswal breed of cattle.

Estimated genetic associations among reproductive traits in Nellore cattle using Bayesian analysis

Scrotal circumference of bulls is correlated with pubertal age of female offspring. Hormonal control of reproductive function is similar in males and females, which may result in genetic correlation among different reproductive traits measured in the two sexes. The estimation of heritability and genetic correlations allows for the computation of direct and correlated genetic gains which are important for predicting of outcomes as a result of genetic-based selection. The aim of this study was to estimate genetic parameters and relative efficiency of indirect selection for age at first calving (AFC), stayability (STAY) and scrotal circumference at 365 days of age (SC365) in Nellore cattle. The STAY variable can be defined as the probability of a cow remain in the herd enough time to raise a certain number of calves that pay for her development and maintenance costs. A bivariate Bayesian analysis was used to estimate variance components using a linear-animal model for SC365 and AFC and threshold-linear model for SC365 and STAY and for AFC and STAY. For STAY, the value of 1 was assigned to cows that calved at least three times by 76 months of age; otherwise, the value 0 was assigned. The posteriori means of heritability estimates were 0.29, 0.08 and 0.09 for SC365, AFC and STAY, respectively. Genetic correlations were favorable from a cow productivity perspective between SC365 and AFC, and SC365 and STAY (-0.45 and 0.12, respectively). Indirect selection approaches were more efficient than direct selection for AFC (ERS = 1.87) when animals were selected for SC365.

Sexual selection and inbreeding: Two efficient ways to limit the accumulation of deleterious mutations.

Theory and empirical data showed that two processes can boost selection against deleterious mutations, thus facilitating the purging of the mutation load: inbreeding, by exposing recessive deleterious alleles to selection in homozygous form, and sexual selection, by enhancing the relative reproductive success of males with small mutation loads. These processes tend to be mutually exclusive because sexual selection is reduced under mating systems that promote inbreeding, such as self‐fertilization in hermaphrodites. We estimated the relative efficiency of inbreeding and sexual selection at purging the genetic load, using 50 generations of experimental evolution, in a hermaphroditic snail (Physa acuta). To this end, we generated lines that were exposed to various intensities of inbreeding, sexual selection (on the male function), and nonsexual selection (on the female function). We measured how these regimes affected the mutation load, quantified through the survival of outcrossed and selfed juveniles. We found that juvenile survival strongly decreased in outbred lines with reduced male selection, but not when female selection was relaxed, showing that male‐specific sexual selection does purge deleterious mutations. However, in lines exposed to inbreeding, where sexual selection was also relaxed, survival did not decrease, and even increased for self‐fertilized juveniles, showing that purging through inbreeding can compensate for the absence of sexual selection. Our results point to the further question of whether a mixed strategy combining the advantages of both mechanisms of genetic purging could be evolutionary stable.

Increasing accuracy and reducing costs of genomic prediction by marker selection

Genotyping costs can be reduced without decreasing the genomic selection accuracy through methodologies of markers subsets assortment. Thus, we compared two strategies to obtain markers subsets. The former uses the primary and the latter the re-estimated markers effects. Moreover, we analyzed each subset via prediction accuracy, bias, and relative efficiency by main genotypic effect model (MGE) fitted, using genomic best linear unbiased predictor linear kernel (GB), and Gaussian nonlinear kernel (GK). All scenarios (subset of markers × kernels models) were applied to a public dataset of rice diversity panel (RICE) and two hybrids maize datasets (HEL and USP). The highest prediction accuracies were obtained by MGE-GB and MGE-GK for grain yield and plant height when we decrease the number of markers. Overall, marker subsets via re-estimated effects method showed a higher relative efficiency of genomic selection. Based on a high-density panel, we can conclude that it is possible to select the most informative markers in order to improve accuracy and build a low-cost SNP chip to implement genomic selection in breeding programs. In addition, we recommend REE (re-estimated effect) strategies to find markers subsets in training population, increasing accuracy of genomic selection.

Comparison of Marker-Based Genomic Estimated Breeding Values and Phenotypic Evaluation for Selection of Bacterial Spot Resistance in Tomato.

Bacterial spot affects tomato crops (Solanum lycopersicum) grown under humid conditions. Major genes and quantitative trait loci (QTL) for resistance have been described, and multiple loci from diverse sources need to be combined to improve disease control. We investigated genomic selection (GS) prediction models for resistance to Xanthomonas euvesicatoria and experimentally evaluated the accuracy of these models. The training population consisted of 109 families combining resistance from four sources and directionally selected from a population of 1,100 individuals. The families were evaluated on a plot basis in replicated inoculated trials and genotyped with single nucleotide polymorphisms (SNP). We compared the prediction ability of models developed with 14 to 387 SNP. Genomic estimated breeding values (GEBV) were derived using Bayesian least absolute shrinkage and selection operator regression (BL) and ridge regression (RR). Evaluations were based on leave-one-out cross validation and on empirical observations in replicated field trials using the next generation of inbred progeny and a hybrid population resulting from selections in the training population. Prediction ability was evaluated based on correlations between GEBV and phenotypes (rg), percentage of coselection between genomic and phenotypic selection, and relative efficiency of selection (rg/rp). Results were similar with BL and RR models. Models using only markers previously identified as significantly associated with resistance but weighted based on GEBV and mixed models with markers associated with resistance treated as fixed effects and markers distributed in the genome treated as random effects offered greater accuracy and a high percentage of coselection. The accuracy of these models to predict the performance of progeny and hybrids exceeded the accuracy of phenotypic selection.

Relative efficiency of positive selection and tissue culture for generating pathogen-free planting materials of yam (Dioscorea spp.)

Yams are staples in West Africa. They are propagated from tubers in an informal seed system. This encourages a build-up of diseases, and necessitates the rapid development of a formal seed system where certified seeds are functional. Although few reports exist on the use of meristem culture to generate pathogen-free yam, the success rate for the most economically important species in the sub-region, Dioscorea rotundata, for the most prevalent viruses is inadequate. To generate pathogen-free yam planting materials, the relative efficiency of tissue culture and positive selection was compared. Twenty-one asymptomatic yam plants were positively selected from 8187 stands of five landraces. Five of these stands were tested virus-negative by multiplex polymerase chain reaction (PCR) for Yam mosaic virus (YMV), Yam mild mosaic virus (YMMV) and Cucumber mosaic virus (CMV), and by PCR for the genus Badnavirus (BV), giving 0.08% success. Single nodes of the positively selected stands were used to establish in vitro plantlets, which were screened onto bacteriological indexing medium. The same was done for meristem- and node-derived plantlets of the improved variety TDr 95/19158. Incidence of endophytes ranged from 18 to 32% in the nodal plantlets while it was 0% in the meristem-derived plantlets. The effect of meristem culture combined with thermotherapy on the virus infection status was determined using virus-tested, one week old in vitro plantlets of eight improved genotypes. These in vitro plantlets were incubated at 36 ± 0.5°C and 16 h photoperiod for 21 days, after which meristems were excised, regenerated into plantlets and re-tested for viruses. Seventy-three percent of the samples were recovered from YMV but the effect on BV was inconsistent. Positive selection can be used as a palliative in generating quality declared seed but meristem culture combined with thermotherapy is more efficient for generating certified seed tubers of yam.

Identification of morphological traits using smith index for grain yield improvement in oat (Avena sativa L.)

Selection indices were constructed using seven traits in a set of 32 forage oat (Avena sativa L.) genotypes using Smith index. The experiment was conducted with three replications at Instructional Dairy Farm, G.B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand. The efficiency of different indices was assessed in terms of expected genetic advance and relative efficiency of selection over grain yield per se. Efficiency of indices over direct selection for relative selection efficiency ranged from 16.92 to 514.28 percent. Selection on the basis of number of spikelets per panicle gave 43.16% higher efficiency for grain yield improvement. This trait was found important for all the indices that also had high heritability, high GCV and direct effect on grain yield per plant. Selection indices comprising of growth rate, number of spikelets per panicle and grain yield were most efficient indices for grain yield improvement with relative efficiency of selection as 374.53 percent and genetic advance of 24.12.

Use of spectral reflectance for indirect selection of yield potential and stability in Pacific Northwest winter wheat

The use of canopy spectral reflectance as a high throughput selection method has been recommended to augment genetic gain from yield based selection in highly variable environments. The objectives of this study were to estimate genotypic correlations between grain yield and spectral reflectance indices (SRIs), and estimate heritability, expected response to selection, relative efficiency of indirect selection, and accuracy of yield predictive models in Pacific Northwest winter wheat (Triticum aestivum L.) under a range of moisture regimes. A diversity panel of 402 winter wheat genotypes (87 hard and 315 soft) was grown in rain-fed and irrigated conditions across the eastern Washington in 2012 and 2013. Canopy spectral reflectance measured at heading, milk, soft dough, and hard dough stages were used to derive several SRIs which generally had higher broad sense heritability (H2) than yield per se. Grain yield and SRIs showed generally high genetic variability and response to selection in moist-cool rain-fed condition. Efficiency of indirect selection for yield using SRIs was high in drought environment and exceeded efficiency of yield-based selection in the soft winter subgroup. Normalized water band index (NWI) showed consistent response to selection across environments, higher genetic correlation with yield (0.51–0.80, p<0.001), and highest indirect selection efficiency (up to 143%). A yield predictive model with one or more SRIs explained 41–82% of total variation in grain yield (p<0.001). The repeatability of genotypic performance between years increased when selection was conducted based on both SRIs and grain yield compared to selection based on yield or SRI alone. The generally high heritability of SRIs and their significant genotypic correlation with grain yield highlight the possibility to improve yield and yield stability in winter wheat through remotely sensed phenotyping approaches.

Seleção para a produção de ovos em períodos parciais e acumulados em linhagem de frango de corte comercial

Objetivou-se com este estudo estimar parâmetros genéticos para produções parciais e acumuladas de ovos em uma linha fêmea de frangos de corte comercial. Foram considerados 10 períodos mensais entre 25 e 64 semanas, três períodos parciais de 25 a 32, 33 a 48 e 49 a 64 semanas, e três períodos acumulados de 25 até 30, 40 e 50 semanas de idade. Os componentes de covariância e parâmetros genéticos foram obtidos pelo método da máxima verossimilhança restrita, sob o modelo animal considerando o efeito fixo de incubação e os efeitos aleatórios genético aditivo e residual. As estimativas de herdabilidade variaram de 0,12 a 0,41. Evidenciou-se que os períodos anteriores e posteriores ao maior nível de produção apresentam maior variabilidade genética. As correlações genéticas entre os períodos de produção de ovos estudados variaram de -0,12 a 0,98. De modo geral, o padrão de variação foi semelhante entre as estratégias avaliadas, e todas foram geneticamente associadas com a produção total. Os resultados deste estudo mostraram que a melhoria da produção total é viável por meio de seleção de registros parciais. No entanto, caso se considere a eficiência relativa de seleção, o segundo mês e os períodos a partir da quadragésima semana de produção seriam os mais indicados.

Selection indices in groundnut (Arachis hypogaea L.)

Fifty diverse genotypes of groundnut were evaluated in a randomized block design with three replications for the study of selection indices during summer 2014. Thirty-one selection indices involving pod yield per plant (X1) and four yield components viz., kernel yield per plant (X2) harvest index (X3), number of mature pods per plant (X4) and biological yield per plant (X5) were constructed using the discriminant function technique. Discriminant function analysis indicated that selection efficiency of the function was improved by increasing the number of characters in the index. Among the single character indices, biological yield per plant exhibited higher genetic advance and relative efficiency over straight selection for pod yield per plant. The index based on five characters viz., pod yield per plant, kernel yield per plant, harvest index, number of mature pods per plant and biological yield per plant recorded the highest genetic advance as well as relative efficiency and selection efficiency. These characters could be advantageously exploited in the groundnut breeding programmes.