Genetic parameters for growth, wood density and pulp yield in Eucalyptus globulus

Genetic variation and co-variation among the key pulpwood selection traits for Eucalyptus globulus were estimated for a range of sites in Portugal, with the aim of improving genetic parameters used to predict breeding values and correlated response to selection. The trials comprised clonally replicated full-sib families (eight trials) and unrelated clones (17 trials), and exhibited varying levels of pedigree connectivity. The traits studied were stem diameter at breast height, Pilodyn penetration (an indirect measure of wood basic density) and near infrared reflectance predicted pulp yield. Univariate and multivariate linear mixed models were fitted within and across sites, and estimates of additive genetic, total genetic, environmental and phenotypic variances and covariances were obtained. All traits studied exhibited significant levels of additive genetic variation. The average estimated within-site narrow-sense heritability was 0.19 ± 0.03 for diameter and 0.29 ± 0.03 for Pilodyn penetration, and the pooled estimate for predicted pulp yield was 0.42 ± 0.14. When they could be tested, dominance and epistatic effects were generally not statistically significant, although broad-sense heritability estimates were slightly higher than narrow-sense heritability estimates. Averaged across trials, positive additive (0.64 ± 0.08), total genetic (0.58 ± 0.04), environmental (0.38 ± 0.03) and phenotypic (0.43 ± 0.02) correlation estimates were consistently obtained between diameter and Pilodyn penetration. This data argues for at least some form of pleiotropic relationship between these two traits and that selection for fast growth will adversely affect wood density in this population. Estimates of the across-site genetic correlations for diameter and Pilodyn penetration were high, indicating that the genotype by environment interaction is low across the range of sites tested. This result supports the use of single aggregated selection criteria for growth and wood density across planting environments in Portugal, as opposed to having to select for performance in different environments.     

Genetic architecture of fruit quality traits in Malus x domestica (Borkh.) compared between own-rooted seedlings and vegetative propagules on ��M. 9�� rootstock

The comparative performance of vegetative propagules (VP) grafted on ‘M. 9’ rootstock and own-rooted (OR) seedlings of the same genotypes was investigated for apple [Malus x domestica (Borkh.)] fruit quality traits using offspring from 22 control-pollinated families. Fifteen fruit quality traits including fruit size and shape, skin colour, russet and sensory eating characteristics were evaluated for individual seedlings. Estimates of genetic variance–covariance matrices (G) were obtained and compared between the two treatments (OR versus VP) using Mantel’s test and regression approaches. Empirical estimates of correlations, at the individual-tree and family-mean levels, between the two treatments were compared with those obtained from deterministic simulations. Estimates of narrow-sense heritability (h ²) were higher in the VP population than in the OR population for 11 of the 15 traits. The estimated G matrices were significantly different between the two treatments. Simulation study showed that with an increase in the total genetic variance, the correspondence between the two treatments at the family-mean level improved dramatically for different family sizes. As the ratio of dominance/additive variance increased from 0 to 1, the family-mean correlations between the two treatments decreased for all family sizes. The average estimated correlations between the two treatments at the family-mean level were higher than at the individual-tree level (0.78 and 0.42, respectively). These observed correlations were very similar to our theoretical expectations. In the light of these results, caution is required when comparing apple seedlings tested on their own roots with those tested on ‘M. 9’ rootstock, as potential cultivar breeding parents.     

Quantitative trait loci for resistance against powdery mildew in a segregating wheat×spelt population

 Powdery mildew is one of the major diseases of wheat in regions with a maritime or semi-continental climate and can strongly affect grain yield. The attempt to control powdery mildew with major resistance genes (Pm genes) has not provided a durable resistance. Breeding for quantitative resistance to powdery mildew is more promising, but is difficult to select on a phenotypic basis. In this study, we mapped and characterised quantitative trait loci (QTLs) for adult-plant powdery mildew resistance in a segregating population of 226 recombinant inbred lines derived from the cross of the Swiss wheat variety Forno with the Swiss spelt variety Oberkulmer. Forno possibly contains the Pm5 gene and showed good adult-plant resistance in the field. Oberkulmer does not have any known Pm gene and showed a moderate susceptible reaction. Powdery mildew resistance was assessed in field trials at two locations in 1995 and at three locations in 1996. The high heritability (h²=0.97) for powdery mildew resistance suggests that the environmental influence did not affect the resistance phenotype to a great extent. QTL analysis was based on a genetic map containing 182 loci with 23 linkage groups (2469 cM). With the method of composite interval mapping 18 QTLs for powdery mildew resistance were detected, explaining 77% of the phenotypic variance in a simultaneous fit. Two QTLs with major effects were consistent over all five environments. One of them corresponds to the Pm5 locus derived from Forno on chromosome 7B. The other QTL on 5A, was derived from the spelt variety Oberkulmer and did not correspond to any known Pm gene. In addition, five QTLs were consistent over three environments, and six QTLs over two environments. The QTL at the Pm5 locus showed a large effect, although virulent races for Pm5 were present in the mixture of isolates. Molecular markers linked with QTLs for adult-plant resistance offer the possibility of simultaneous marker-assisted selection for major and minor genes. Received: 22 September 1998 / Accepted: 26 October 1998     

Genetic linkage map of melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) and localization of a major QTL for powdery mildew resistance

Powdery mildew caused by Podosphaera xanthii has become a major problem in melon since it occurs all year round irrespective of the growing system. The TGR-1551 melon genotype was found to be resistant to several melon diseases, among them powdery mildew. However, the corresponding resistance genes have been never mapped. We constructed an integrated genetic linkage map using an F2 population derived from a cross between the multi-resistant genotype TGR-1551 and the susceptible Spanish cultivar ‘Bola de Oro’. The map spans 1,284.9 cM, with an average distance of 3.6 cM among markers, and consists of 354 loci (188 AFLP, 39 RAPD, 111 SSR, 14 SCAR/CAPS/dCAPS, and two phenotypic traits) distributed in 14 linkage groups. QTL analysis identified one major QTL (Pm-R) on LG V for resistance to races 1, 2, and 5 of powdery mildew. The PM4-CAPS marker is closely linked to the Pm-R QTL at a genetic distance of 1.9 cM, and the PM3-CAPS marker is located within the support interval of this QTL. These codominant markers, together with the map information reported here, could be used for melon breeding, and particularly for genotyping selection of resistance to powdery mildew in this vegetable crop species.     

Using a limited mapping strategy to identify major QTLs for resistance to grapevine powdery mildew (<Emphasis Type="Italic">Erysiphe necator</Emphasis>) and their use in marker-assisted breeding

A limited genetic mapping strategy based on simple sequence repeat (SSR) marker data was used with five grape populations segregating for powdery mildew (Erysiphe necator) resistance in an effort to develop genetic markers from multiple sources and enable the pyramiding of resistance loci. Three populations derived their resistance from Muscadinia rotundifolia ‘Magnolia’. The first population (06708) had 97 progeny and was screened with 137 SSR markers from seven chromosomes (4, 7, 9, 12, 13, 15, and 18) that have been reported to be associated with powdery or downy mildew resistance. A genetic map was constructed using the pseudo-testcross strategy and QTL analysis was carried out. Only markers from chromosome 13 and 18 were mapped in the second (04327) and third (06712) populations, which had 47 and 80 progeny, respectively. Significant QTLs for powdery mildew resistance with overlapping genomic regions were identified for different tissue types (leaf, stem, rachis, and berry) on chromosome 18, which distinguishes the resistance in ‘Magnolia’ from that present in other accessions of M. rotundifolia and controlled by the Run1 gene on chromosome 12. The ‘Magnolia’ resistance locus was termed as Run2.1. Powdery mildew resistance was also mapped in a fourth population (08391), which had 255 progeny and resistance from M. rotundifolia ‘Trayshed’. A locus accounting for 50% of the phenotypic variation mapped to chromosome 18 and was named Run2.2. This locus overlapped the region found in the ‘Magnolia’-based populations, but the allele sizes of the flanking markers were different. ‘Trayshed’ and ‘Magnolia’ shared at least one allele for 68% of the tested markers, but alleles of the other 32% of the markers were not shared indicating that the two M. rotundifolia selections were very different. The last population, 08306 with 42 progeny, derived its resistance from a selection Vitis romanetii C166-043. Genetic mapping discovered a major powdery mildew resistance locus termed Ren4 on chromosome 18, which explained 70% of the phenotypic variation in the same region of chromosome 18 found in the two M. rotundifolia resistant accessions. The mapping results indicate that powdery mildew resistance genes from different backgrounds reside on chromosome 18, and that genetic markers can be used as a powerful tool to pyramid these loci and other powdery mildew resistance loci into a single line.     

A major QTL for powdery mildew resistance is stable over time and at two development stages in winter wheat

Despite the large impact of powdery mildew in wheat cultivated areas, little has been done to study powdery mildew resistance by QTL analysis up to now. The objective of the present paper is to present how the genetic basis of powdery mildew resistance in the resistant wheat line RE714 have been studied by QTL analysis at the adult plant stage over the course of 3 years, and at the vernalized seedling plant stage, and a comparison between the results obtained. Two segregating populations (DH and F_2:3) were derived from the cross between the resistant line (RE714), and a susceptible line (Hardi); these were analysed for powdery mildew resistance at the adult plant stage in the field under natural infection conditions in 1996, 1997 and 1998. The DH population was also tested for powdery mildew resistance at the vernalized seedling stage with four different isolates of powdery mildew. At the adult plant stage, a total of three QTLs (on chromosomes 5D, 4A and 6A) and five QTLs (on chromosomes 5D, 6A, 7A and 7B) were found for the DH and F_2:3 populations, respectively. The genetic control of resistance was found to be polygenic but involved a major QTL (on chromosome 5D), which was detected each year and which explained a high proportion of the variability observed (28.1%–37.9%). At the vernalized seedling stage, two QTLs were found (on chromosomes 5D and 7B) and the QTL detected on chromosome 5D was common to the four isolates tested. The comparison between the two development stages showed that the QTL on chromosome 5D was detected in all the different environments tested and again explained a high proportion of the variability. Different molecular interpretations of this QTL have also been discussed. Received: 5 October 2000 / Accepted: 1 March 2001     

Heritability estimates from genomewide relatedness matrices in wild populations: Application to a passerine,using a small sample size

Genomic developments have empowered the investigation of heritability in wild populations directly from genomewide relatedness matrices (GRM). Such GRM‐based approaches can in particular be used to improve or substitute approaches based on social pedigree (PED‐social). However, measuring heritability from GRM in the wild has not been widely applied yet, especially using small samples and in nonmodel species. Here, we estimated heritability for four quantitative traits (tarsus length, wing length, bill length and body mass), using PED‐social, a pedigree corrected by genetic data (PED‐corrected) and a GRM from a small sample (n = 494) of blue tits from natural populations in Corsica genotyped at nearly 50,000 filtered SNPs derived from RAD‐seq. We also measured genetic correlations among traits, and we performed chromosome partitioning. Heritability estimates were slightly higher when using GRM compared to PED‐social, and PED‐corrected yielded intermediate values, suggesting a minor underestimation of heritability in PED‐social due to incorrect pedigree links, including extra‐pair paternity, and to lower information content than the GRM. Genetic correlations among traits were similar between PED‐social and GRM but credible intervals were very large in both cases, suggesting a lack of power for this small data set. Although a positive linear relationship was found between the number of genes per chromosome and the chromosome heritability for tarsus length, chromosome partitioning similarly showed a lack of power for the three other traits. We discuss the usefulness and limitations of the quantitative genetic inferences based on genomic data in small samples from wild populations.     

Development of SCAR markers linked to powdery mildew (<Emphasis Type="Italic">Uncinula necator</Emphasis>) resistance in grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L. and <Emphasis Type="Italic">Vitis</Emphasis> sp.)

Sequence-characterized amplified regions markers (SCARs) were developed from six randomly amplified polymorphic DNA (RAPD) markers linked to the major QTL region for powdery mildew (Uncinula necator) resistance in a test population derived from the cross of grapevine cultivars “Regent” (resistant) × “Lemberger”(susceptible). RAPD products were cloned and sequenced. Primer pairs with at least 21 nucleotides primer length were designed. All pairs were tested in the F1 progeny of “Regent” × “Lemberger”. The SCAR primers resulted in the amplification of specific bands of expected sizes and were tested in additional genetic resources of resistant and susceptible germplasm. All SCAR primer pairs resulted in the amplification of specific fragments. Two of the SCAR markers named ScORA7-760 and ScORN3-R produced amplification products predominantly in resistant individuals and were found to correlate to disease resistance. ScORA7-760, in particular, is suitable for marker-assisted selection for powdery mildew resistance and to facilitate pyramiding powdery mildew resistance genes from various sources.     

Selection and genetic (co)variance in bighorn sheep

Genetic theory predicts that directional selection should deplete additive genetic variance for traits closely related to fitness, and may favor the maintenance of alleles with antagonistically pleiotropic effects on fitness-related traits. Trait heritability is therefore expected to decline with the degree of association with fitness, and some genetic correlations between selected traits are expected to be negative. Here we demonstrate a negative relationship between trait heritability and association with lifetime reproductive success in a wild population of bighorn sheep (Ovis canadensis) at Ram Mountain, Alberta, Canada. Lower heritability for fitness-related traits, however, was not wholly a consequence of declining genetic variance, because those traits showed high levels of residual variance. Genetic correlations estimated between pairs of traits with significant heritability were positive. Principal component analyses suggest that positive relationships between morphometric traits constitute the main axis of genetic variation. Trade-offs in the form of negative genetic or phenotypic correlations among the traits we have measured do not appear to constrain the potential for evolution in this population.     

Estimation of genetic parameters and prediction of breeding values for apple fruit-quality traits using pedigreed plant material in Europe

Genetic parameters for apple (Malus x domestica) fruit external traits (fruit size, ground colour, proportion of over colour and attractiveness) and sensory traits (firmness, crispness, texture, juiciness, flavour, sugar, acidity and global taste) were estimated using 2,207 pedigreed genotypes from breeding programmes in six European countries. Data were scored for 3 years and four periods during storage. Analyses were performed with a restricted maximum likelihood method using VCE 5.1.2 software. Heritability estimates ranged from medium to high for instrumental traits. Genetic correlations between firmness and sugar were medium and low between firmness and acidity. Sensory traits showed low to high heritability, acidity and flavour being, respectively, the most and the less heritable. Global taste was strongly correlated with texture, juiciness, and flavour and relatively less correlated with crispness and acidity. Sensory sugar and acidity showed highly negative correlations whereas their instrumental measurements showed low and increasing positive correlations from harvest to 4 months post-harvest. Sugar exhibited a higher sensory/instrumental divergence. Conversely, instrumental and sensory firmness were highly correlated. Fruit external characteristics had medium heritability. Fruit attractiveness had highest and lowest correlations with fruit size and ground colour, respectively. Best linear unbiased predictors of breeding values were computed for all genotypes with the software PEST. The results were analysed with regard to the dynamic and the reliability of genetic parameters according to the scoring dates. Original issues of the study and the importance of the obtained results for efficient designs of further apple fruit quality breeding programmes were discussed.     

Field resistance of spring barley cultivars to powdery mildew in Lithuania

During vegetative period 2004–2005 powdery mildew (Erysiphe graminis DC. f. sp. hordei Em. Marchal) field resistance of spring barley cultivars was investigated at the Lithuanian Institute of Agriculture. The spring barley genotypes tested were Lithuania-registered cultivars, cultivars from genetic resources collection, and the new cultivars used for initial breeding. In total, 23 resistance genes were present in the 84 cultivars studied. Among mono-genes only mlo and 1-B-53 showed very high resistance. Slight powdery mildew necroses (up to 3 scores) formed on cultivars possessing these genes. The maximal powdery mildew (PM) severity reached a score of 8.5 and the area under disease progress curve (AUDPC) a value of 1216.8. The cultivars ‘Primus’, ‘Astoria’, ‘Power’, ‘Harrington’ and ‘Scarlett’ were the most resistant among the non mlo cultivars. Severity of PM on ‘Primus’ reached a score of 3.5 (3.0 of PM necrosis) in average, the other cultivars were diseased from 4.5 (3.0) to 5.0 (2.0). The AUDPC values for these cultivars except ‘Scarlett’ were the lowest (85.0–145.3) among the other cultivars. The highest contrast in development of the other leaf diseases was between highly resistant and susceptible to PM cultivar groups. The fast development of PM depressed development of the other diseases 4.7 times.     

Identification of SCAR markers linked to <Emphasis Type="Italic">Pl-w</Emphasis> mildew resistance in apple

Resistance to powdery mildew is an important objective for cultivar improvement programmes of apple and several different major genes for resistance to mildew are available. Molecular markers linked to such key traits can be used to screen progenies for resistant individuals. A progeny derived from the crab apple 'White Angel' (the source of Pl-w) was screened for resistance to mildew for two seasons in the glasshouse and four seasons in the field. DNA bulks of resistant and susceptible seedlings were screened with 176 AFLP primer combinations. Seven AFLP markers were identified that differentiated the bulks, and two of these markers were developed into SCARs, EM M01 and EM M02, mapping at 4.6 and 6.4 recombination units from Pl-w.     

烟草白粉病抗性基因的遗传分析

以烟草抗白粉病品种台烟7号为母本,感病品种NC89为父本,构建6个世代的群体,利用主基因 多基因混合遗传模型的分离分析方法,研究烟草白粉病的抗性遗传规律。结果表明,烟草白粉病抗性的遗传是由两对加性-显性-上位性主基因 加性-显性-上位性多基因（E-0模型）控制的。B1、B2和F2世代主基因的遗传率分别为88.05%、32.62%、84.43%,主基因遗传率很大,说明可以在抗病育种早期进行选择;B1、F2世代多基因遗传率均为0.00%,说明烟草白粉病的发生受一定环境影响。     

RAPDs as molecular markers for the detection of Aegilops markgrafii chromatin in addition and euploid introgression lines of hexaploid wheat

 Aegilops markgrafii contains resistance genes to powdery mildew, leaf rust and stripe rust, and also has high crude protein and lysine contents, which can be useful for wheat improvement. These important traits are localized on different chromosomes. Disomic Triticum aestivum-Ae. markgrafii addition lines and euploid introgression lines showing leaf-rust and powdery mildew resistance were screened with RAPDs to detect chromosome-specific markers which can accelerate the breeding process. RAPD markers for all six available disomic addition lines were obtained. The additional chromosomes B, C, D, E, F and G were identified by three, three, three, two, one and seven primers, respectively. All three chromosome-B-specific RAPD markers demonstrated the presence of alien chromatin in the leaf-rust-resistant 42-chromosome introgression lines as well as in the segregating progeny. The three chromosome-C-identifying primers also demonstrated the presence of that chromosome in powdery mildew-resistant euploid introgression lines. The substitution lines (5A)5C and (5D)5C with different genetic backgrounds for both parents, in comparison to the lines mentioned above, showed the chromosome C-specific band with only two of the three primers. The chromosome F-specific primer and a primer evident on all the Ae. markgrafii chromosomes analysed did not generate the expected fragments on the chromosome F_del addition line, indicating that the markers are located on the deleted part of chromosome F. Received: 20 August 1996 / Accepted 17 January 1997     

Heritability and genetic correlations of personality traits in a wild population of yellow‐bellied marmots (Marmota flaviventris)

Describing and quantifying animal personality is now an integral part of behavioural studies because individually distinctive behaviours have ecological and evolutionary consequences. Yet, to fully understand how personality traits may respond to selection, one must understand the underlying heritability and genetic correlations between traits. Previous studies have reported a moderate degree of heritability of personality traits, but few of these studies have either been conducted in the wild or estimated the genetic correlations between personality traits. Estimating the additive genetic variance and covariance in the wild is crucial to understand the evolutionary potential of behavioural traits. Enhanced environmental variation could reduce heritability and genetic correlations, thus leading to different evolutionary predictions. We estimated the additive genetic variance and covariance of docility in the trap, sociability (mirror image stimulation), and exploration and activity in two different contexts (open‐field and mirror image simulation experiments) in a wild population of yellow‐bellied marmots (Marmota flaviventris). We estimated both heritability of behaviours and of personality traits and found nonzero additive genetic variance in these traits. We also found nonzero maternal, permanent environment and year effects. Finally, we found four phenotypic correlations between traits, and one positive genetic correlation between activity in the open‐field test and sociability. We also found permanent environment correlations between activity in both tests and docility and exploration in the MIS test. This is one of a handful of studies to adopt a quantitative genetic approach to explain variation in personality traits in the wild and, thus, provides important insights into the potential variance available for selection.     

Identification of QTLs for resistance to powdery mildew and SSR markers diagnostic for powdery mildew resistance genes in melon (Cucumis melo L.)

Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible ‘Earl’s Favourite (Harukei 3)’. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R ² = 22–28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41–46%) than that on LG IIA (12–13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.     

QTL analysis for aphid resistance and growth traits in apple

The rosy apple aphid (Dysaphis plantaginea), the leaf-curling aphid (Dysaphis cf. devecta) and the green apple aphid (Aphis pomi) are widespread pest insects that reduce growth of leaves, fruits and shoots in apple (Malus × domestica). Aphid control in apple orchards is generally achieved by insecticides, but alternative management options like growing resistant cultivars are needed for a more sustainable integrated pest management (IPM). A linkage map available for a segregating F₁-cross of the apple cultivars ‘Fiesta’ and ‘Discovery’ was used to investigate the genetic basis of resistance to aphids. Aphid infestation and plant growth characteristics were repeatedly assessed for the same 160 apple genotypes in three different environments and 2 consecutive years. We identified amplified fragment length polymorphism (AFLP) markers linked to quantitative trait loci (QTLs) for resistance to D. plantaginea (‘Fiesta’ linkage group 17, locus 57.7, marker E33M35–0269; heritability: 28.3%), and to D. cf. devecta (‘Fiesta’ linkage group 7, locus 4.5, marker E32M39–0195; heritability: 50.2%). Interactions between aphid species, differences in climatic conditions and the spatial distribution of aphid infestation were identified as possible factors impeding the detection of QTLs. A pedigree analysis of simple sequence repeat (SSR) marker alleles closely associated with the QTL markers revealed the presence of the alleles in other apple cultivars with reported aphid resistance (‘Wagener’, ‘Cox’s Orange Pippin’), highlighting the genetic basis and also the potential for gene pyramiding of aphid resistance in apple. Finally, significant QTLs for shoot length and stem diameter were identified, while there was no relationship between aphid resistance and plant trait QTLs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

QTL analysis of powdery mildew resistance in cucumber (Cucumis sativus L.)

A population of F₇ recombinant inbred lines (RILs) was made from a cross between susceptible (‘Santou’) and resistant (PI197088-1) lines of cucumber in order to study powdery mildew resistance loci. Susceptibility to powdery mildew in the F₇ RIL individuals showed a continuous distribution from susceptible to resistant, suggesting that powdery mildew resistance is controlled by quantitative trait loci (QTLs). A QTL analysis identified two and three loci for powdery mildew resistance under 26 and 20°C conditions, respectively. One QTL was found in the same position under both temperature conditions. Therefore, it is more likely that one major QTL acts under both temperature conditions and that other QTLs are specific to the two temperature conditions. The above results suggest that the four QTLs are controlled in a different temperature manner, and that their combination played an important role in expressing a high level of resistance to powdery mildew in this cucumber population. Sequence-tagged site (STS) markers associated with each QTL were developed and would be useful for breeding a cucumber line with a high level of powdery mildew resistance. Y. Sakata and N. Kubo contributed equally to this work and are considered as first authors.     

A multi-marker test based on family data in genome-wide association study

Background

Requirements for successful implementation of multivariate animal threshold models including phenotypic and genotypic information are not known yet. Here simulated horse data were used to investigate the properties of multivariate estimators of genetic parameters for categorical, continuous and molecular genetic data in the context of important radiological health traits using mixed linear-threshold animal models via Gibbs sampling. The simulated pedigree comprised 7 generations and 40000 animals per generation. Additive genetic values, residuals and fixed effects for one continuous trait and liabilities of four binary traits were simulated, resembling situations encountered in the Warmblood horse. Quantitative trait locus (QTL) effects and genetic marker information were simulated for one of the liabilities. Different scenarios with respect to recombination rate between genetic markers and QTL and polymorphism information content of genetic markers were studied. For each scenario ten replicates were sampled from the simulated population, and within each replicate six different datasets differing in number and distribution of animals with trait records and availability of genetic marker information were generated. (Co)Variance components were estimated using a Bayesian mixed linear-threshold animal model via Gibbs sampling. Residual variances were fixed to zero and a proper prior was used for the genetic covariance matrix.

Results

Effective sample sizes (ESS) and biases of genetic parameters differed significantly between datasets. Bias of heritability estimates was -6% to +6% for the continuous trait, -6% to +10% for the binary traits of moderate heritability, and -21% to +25% for the binary traits of low heritability. Additive genetic correlations were mostly underestimated between the continuous trait and binary traits of low heritability, under- or overestimated between the continuous trait and binary traits of moderate heritability, and overestimated between two binary traits. Use of trait information on two subsequent generations of animals increased ESS and reduced bias of parameter estimates more than mere increase of the number of informative animals from one generation. Consideration of genotype information as a fixed effect in the model resulted in overestimation of polygenic heritability of the QTL trait, but increased accuracy of estimated additive genetic correlations of the QTL trait.

Conclusion

Combined use of phenotype and genotype information on parents and offspring will help to identify agonistic and antagonistic genetic correlations between traits of interests, facilitating design of effective multiple trait selection schemes.