Modified full-sib selection and best linear unbiased prediction of progeny performance in a European F2 maize population

Four cycles of modified recurrent full‐sib (FS) selection were conducted in an intermated F₂ population of European flint maize. The objectives of our study were to monitor trends across selection cycles in the estimates of population mean, inbreeding coefficients and variance components, and to investigate the usefulness of best linear unbiased prediction (BLUP) of progeny performance under the recurrent FS selection scheme applied. We used a selection rate of 25% for a selection index, based on grain yield and dry matter content. A pseudo‐factorial mating scheme was used for recombination. In this scheme, the selected FS families were divided into an upper‐ranking group of parents mated to the lower‐ranking group. Variance components were estimated with restricted maximum likelihood (REML). Average grain yield increased 1.2 t/ha per cycle, average grain moisture decreased 20.1 g/kg per cycle, and the selection index relative to the F₂ check entries decreased 0.3% per cycle. For a more precise calculation of selection response, the four cycles should be tested together in multi‐environmental trials. We observed a significant decrease in additive variance in the selection index, suggesting smaller future selection response. Predictions of FS family performance in Cn + 1 based on mean performance of parental FS families in Cn were of equal precision as those based on the mean additive genetic BLUP of their parents, and corresponding correlations were of moderate size for grain moisture and selection index.     

Effect of the number of intercrosses on grain yield in basic rice synthetic populations

The effect of 0, 1, 2, 3 and 4 intercross cycles using genetic male sterility on the mean yield and genetic variability of the CNA 5 irrigated rice synthetic population was assessed studying 300 S_0:2 (1998/99) and S_0:3 (1999/00) families grown in two locations (Lambari, MG and Goianira, GO). Each intercross was investigated using a 8 × 8 triple lattice design experiment containing 60 families and four control cultivars. Five experiments were carried out per location and generation, totaling 20 experiments. Individual, combined over locations, combined over generations and combined over locations and generations analyses of variance were performed. Linear regression equations were fitted to data of each location and generation as well as, genetic and phenotypic parameters were estimated. An average increase of 3.91% in grain yield was obtained with the increase in the number of intercrosses. However, when genetic gains obtained from selection of the five and ten highest yielding families were considered, negative b estimates were always obtained, suggesting a tendency of gain increase reduction with the increase in the number of intercrosses. This was confirmed by the analysis of the means of the best families, since increases in the number of intercrosses did not result in selection of families with greater mean grain yield. The estimates of the genetic variances and heritabilities did not suggest an increase in genetic variability with the increase in intercross cycles. Therefore, carrying out intercrosses on the base population did not improve the results of the irrigated rice recurrent selection program. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of the inbreeding depression in progeny fitness of runner bean (Phaseolus coccineus L.) and it is implications for breeding

Moderate levels of selfing despite high inbreeding depression (ID) make runner bean an excellent model for mixed-mating reproductive biology studies in legumes. This work assesses the extent of the ID variation and consistency at different plant growth stages through selfing generations in seven runner bean populations. Field-collected populations after previous isolated multiplication were hand-pollinated in an isolated greenhouse during five generations to produce progeny. Generations were compared for inbreeding effects (δ) on seed germination, survival to flower, and seed weight and yield. The outcrossing rates of the founder populations and the genetic variation and Wright’s ID at the population and generation level were estimated by using 35 polymorphic microsatellite loci. Neutral microsatellite loci were analyzed through generations and populations using different outlier tests to identify loci directly associated with adaptation to inbreeding. Our study revealed patterns of genetic diversity (H _e  = 0.36) and outcrossing rates (ranged from 24 to 44 %) that are consistent with a mixed-mating system. Selfing-pollination procedure significantly affected germination and survival rates, yield, and to a lesser extent seed weight. Three loci had significant hits to genes related to embryonic development when performing BLAST searches to Phytozome database. Results showed a general inconsistency in δ across plant growth stages and populations, suggesting that different deleterious loci are acting at different stages. Inbreeding tended to purge individuals of deleterious recessive alleles to reduce ID. Variation among individuals within populations may lead to the development of inbreeding lineages with lower levels of ID. Several lines that have been self-pollinated for many generations became homozygous at almost all gene loci and produced a uniform population of true breeding progeny and acceptable performance.     

Effects of inbreeding on cut-flower yield in gerbera

Summary Inbreeding depression for cut-flower yield was found in gerbera (Gerbera hybrida, Compositae). A selection experiment for cut-flower yield in the Davis population was conducted over sixteen generations and the mean cut-flower yield increased from 10.3 flowers to 28.3 flowers. Cut-flower yield was recorded on individual plants grown in the greenhouse and inbreeding coefficients were calculated for each plant based on its pedigree. The effects of inbreeding on yield were estimated by covariance analysis models. The results of this study indicate that first, inbreeding increased 1% per generation in this population and secondly, inbreeding had the negative effect of reducing cut-flower yield by one-quarter flower per generation for every one percent increase in inbreeding.     

Continued response through seven cycles of recurrent selection for grain yield in oat (Avena sativa L.)

Long-term selection experiments provide germplasm to study the effects of selection in a closed population. Recurrent selection to enhance grain yield in oat has been ongoing at the University of Minnesota since 1968. The objectives of this study were: (i) estimate the GCA and SCA effects for three agronomic traits in the seventh cycle of selection, (ii) assess the effect of the current methods of selection on parental contribution and unselected traits, and (iii) determine the direct and indirect responses to seven cycles of recurrent selection for grain yield. Progeny of the Cycle 6 parents and parents for Cycles 0 through 7 were grown in two separate tests. Grain yield, heading date and plant height were evaluated in each test. Grain yield was increased by 21.7% after seven cycles of selection. Evaluation of Cycle 6 progeny showed that GCA effects were significant for all three traits studied, and SCA effects were significant only for grain yield. Four Cycle 6 parents did not have any progeny selected as Cycle 7 parents. Results from this study indicate that long term recurrent selection has continued to increase grain yield. Alternative selection strategies may be necessary to maintain the genetic variability in this population, particularly when improvement of secondary traits is required. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic progress after four cycles of recurrent selection for yield and grain traits in common bean

The objective of this study was to evaluate the genetic progress after four cycles of recurrent selection in common bean. The base segregating population was obtained from 10 parents, and derived the S_0:1 and S_0:2 families that were evaluated. The S_0:3 families with higher grain yield and grain color, like the standard carioca were selected, and were intercrossed to generate the population of the following cycle. This process was repeated for four cycles. The best families were evaluated in each cycle by many generations and locations, and the five best lines of each cycle were identified. The 20 lines thus obtained were evaluated in two growing seasons, sown in July and November 2002. The grain yield (kg/ha) and grain type (scale of scores) were evaluated. Genetic progress was confirmed for both traits. The mean annual gain with selection for the grain type was 10.5% and 5.7% for grain yield, with no evidence of variability reduction in the population. These results show that recurrent selection is a good alternative for improving common bean quantitative traits.     

唐山红小豆地方品种资源数量性状的遗传变异分析

以71份唐山红小豆地方品种资源为研究对像,对资源各数量性状的平均表现、遗传变异、遗传力及预期遗传进度进行了分析。结果表明,唐山红小豆地方品种资源生育期类型单一、株型高大、产量性状较好,子粒大小中等;主茎分枝、单株荚数、单株生产力、小区产量、生育前期、百粒重、单荚粒数具有中等以上的遗传变异系数和遗传进度,对其选择有一定的效果;在选择效果明显的性状中,生育期、百粒重、主茎分枝遗传力较高,可在早代选择;小区产量遗传力中等,可在遗传基础相对稳定的较高世代选择;而株高、单株荚数、单荚粒数、单株生产力的遗传力较低,应在遗传基础纯合稳定的高世代选择。     

An improved breeding strategy for autotetraploid alfalfa (Medicago sativa L.)

Alfalfa cultivar development will be enhanced by breeding strategies whichutilize the full potential of autotetraploid population genetic structures. Thisstudy evaluates the effectiveness of an allelic selection scheme, which wasdeveloped to overcome limitations of inbreeding depression and to exploitgeneral and specific combining ability effects in autotetraploid populations.Allelic selection entails the minimization of non-additive genetic effects byselecting among full-sib families (F1) which are at uniform levels ofheterozygosity. Such F1 lines are developed by crossing individuals fromtwo unrelated random mating populations. Selected F1 lines wereintercrossed to form an improved population. Eight random matingpopulations of alfalfa were developed to study the effectiveness of allelicselection. Selection for increased dry matter yield resulted in alfalfapopulations with 38 percent greater yield than the parent populations. Twocycles of intercrossing, among selected F1 lines, did not dissipate the gainfrom selection. This result has important implications for synthetic cultivardevelopment in which a major limitation is the decline in productivity withadvancing generations of seed increase. A positively correlated response toselection for dry matter yield was observed for plant height and stemdiameter. The results of this research indicate that continued testing of theallelic selection scheme is warranted and could have a significant impact onthe breeding of autotetraploid alfalfa, particularly for synthetic cultivardevelopment.     

Direct and indirect selection for grain yield in oats (avena sativa L.)

Direct and indirect selection for increased grain yield were carried out on a population of 678 F₂-derived lines of oats. A selection intensity of 10% was used with direct selection (selection for grain yield itself) and with indirect selection using three criteria, harvest index, vegetative growth rate, and the index of harvest index + vegetative growth rate. Expected gains from 1978 evaluations were compared to actual gains measured in 1980. Actual grain yield increases were 4, 8, 7, and 6% from selection via harvest index, vegetative growth rate, grain yield, and harvest index + vegetative growth rate, respectively. Thus, indirect selection via vegetative growth rate gave a greater increase in grain yield than did direct selection. Heritability values computed via components of variance ranged from 0.50 to0.57 for the three traits, harvest index, vegetative growth rate, and grain yield, whereas regression heritabilities ranged from 0.41 to 0.55. Realized heritabilities were 0.33, 1.00 and 0.89 for the three traits, respectively. Selection via all criteria caused significant changes in nearly all agronomic traits except weight per volume. Vegetative growth rate, which gave the greatest gain in grain yield, caused less drastic changes in days to anthesis, plant height, biological yield, and vegetative yield than did direct selection for grain yield.     

Marker‐assisted parentage analysis reveals high individual selfing rates in tetraploid red clover genotypes selected for seed yield

Seed yield is a major breeding target in tetraploid red clover. We investigated if marker‐assisted parentage analysis can identify progeny plants with two high seed‐yielding parents in tetraploid red clover and if this technique is more advantageous than traditional half‐sib selection. Parentage analysis was successfully performed on the progeny from the 10% highest seed‐yielding genotypes from a second‐cycle family selection trial: 16.0% of progeny were identified with a high seed‐yielding father. However, progeny plants with two high seed‐yielding parents did not produce more seeds than traditionally selected progeny (27.3 g vs. 30.7 g/plant, respectively). The 10% highest seed‐yielding genotypes displayed on average 2% self‐fertilization. Four genotypes were self‐fertile with individual selfing rates up to 20%. Our results discourage the use of marker‐assisted parentage analysis to improve seed yield in tetraploid red clover when the material has been preselected for seed yield. Breeders should be aware that intensive selection for seed yield in tetraploid red clover may inadvertently lead to selection for increased self‐fertility, which may increase inbreeding in the long term.     

Combining ability of soybean (Glycine max) for low phosphorus tolerance on acidic soils of Western Ethiopia

Determining the gene actions governing the inheritance of traits of interest has paramount importance in designing a breeding approach to improve the progeny populations. This study was undertaken to determine the combining ability of nine selected parental lines in the F₂/F₃ segregating populations for low P tolerance. The experiment was laid out in an alpha lattice design in two locations, that is Mettu and Assossa of Western Ethiopia that are characterized by soils with low P and pH. General combining ability (GCA) effects were highly significant for grain yield, pod length, days to maturity and plant height, while specific combining ability (SCA) effects were highly significant for grain yield, 100-seed weight, pod length and plant height. The parent Hardee-1 was identified as the best general combiner for yield, number of seeds per pod, pod length, plant height and pod number. The results suggest that additive gene action was important for several of the studied traits, implied by significant GCA effect, which might indicate selection for these traits could be effective in later segregating generations.     

不同生态型大豆杂种后代早熟高产性研究

用不同生态来源的6个早熟大豆品种进行完全双列杂交,研究F_1、F_2单株产量等性状的亲子关系、杂种优势,配合力、M·S·g/M·S·s值、遗传力、相关系数。结果表明,早熟大豆杂种F_1、F_2单株产量等性状介于双亲之间,与双亲值、中亲值密切相关;F_2出现超亲分离,分离幅度、杂种优势、特殊配合力效应与双亲生态差异有关,单株粒重与鼓粒—成熟期密切相关,与开花—鼓粒期相关不显著,因此缩短开花—鼓粒期是提高大豆杂种后代早熟高产性的关键。     

Genetic gains in two selection phases of a wheat-breeding programme

Genetic gain in field crops is usually estimated as the collective contribution of several breeding programmes. Critical to an individual breeder, however, is the genetic gain realized within a single programme. Our objective was to quantify per-annum genetic gains from 1969 to 1993 within two successive phases of experimental line testing in the wheat (Triticum aestivum L.) breeding programme of the Oklahoma Agricultural Experiment Station. Data for grain yield (Phases I and II), volume weight and heading date (Phase II) were analysed according to the procedure developed by St. Martin and McBlain (1991). Genetic gains for grain yield were indistinguishable between phases, averaging 4.6 ± 1.1 and 4.2 ± 1.3% of the control mean across the 24-year period. Genetic gain for volume weight averaged only 0.2% of the check mean, reflecting lower selection pressure for that trait compared to grain yield. Inconsistent genetic gains in heading date reflect a preference for a window of desirable heading dates rather than difficulties in selecting uni-directionally for maturity. The absence of a decline in genetic gain in recent years indicates that future improvement in grain yield is likely; however, increased attention must be given to volume weight to maintain US domestic and export standards for hard winter wheat. The statistical procedure was useful in monitoring long-term trends in genetic gains and identifying gaps in programme efficiency.     

Changes in Several Traits of Oats Caused by Selection for Vegetative Growth Rate*

Growth rate and harvest index are the primary components that cause variation in gram yield or oats it growth duration of the crop is fixed as it is in mid western USA. Because harvest index for oats in that region has been optimized 45 %, growth rate is the only remaining trait for improving grain yield. F₂ derived oat lines from inter- (Avena sativa L. ×A. Sterilis L.) and intraspecific mating (among A. sativa cultivars) in F₃ were selected for vegetative growth rate at maturity (GRM) with an intensity of 8.3%. Predicted genetic gain was 21.5% for GRM, and actual gain was 7%. Changes in grain, biological, and straw yields were higher than gains in GRM when expressed as percentages of the oat population means. Predicted genetic gains were very low for traits unrelated or negatively associated with GRM such as heading data and harvest index. This study suggests that indirect improvement can be made for gain, biological, and straw yields by selecting for GRM.     

群体构成方式对大豆百粒重全基因组选择预测准确度的影响

百粒重是大豆产量的重要构成因子,在一定条件下与产量呈显著正相关。百粒重是一个复杂的数量性状,用传统的育种方法其遗传增益不明显。本研究对280份大豆品种多年多点田间鉴定,通过混合线性模型预测获得品种百粒重的最佳线性无偏预测值。同时利用分布在大豆全基因组的5361个SNP标记鉴定参试品种基因型,结合随机回归最佳线性无偏预测模型和交互验证方法,探讨了群体构成方式对大豆百粒重的全基因组选择预测准确度的影响。结果表明,大豆百粒重的全基因组选择预测准确度变化范围为–0.15~ +0.75;群体构成方式对百粒重的预测准确度影响明显;亚群内的预测准确度(0.24~0.75)高于亚群间(?0.15~ +0.29);当群体间遗传距离由0.1566增加到0.2201时,预测准确度下降27.87%;相比随机构建的训练群体,基于群体遗传结构构建的训练群体能将百粒重的预测准确度提高2.34%。本研究明确了大豆百粒重的全基因组选择预测准确度,阐明了群体结构对大豆百粒重的全基因组选择预测准确度的影响,为大豆分子育种提供了新的思路和方法。     

Breeding the common bean (Phaseolus vulgaris L.) for resistance to bean common mosaic virus: alternatives to backcrossing

A series of field experiments was undertaken in order to determine whether resistance to bean common mosaic virus (BCMV) could be incorporated into genotypes of the common bean (Phaseolus vulgaris L.) suitable for cultivation in Zimbabwe without recourse to backcrossing. Six inbred genotypes carrying the resistance-conferring alleles at the loci I and Bc-3 were crossed with five locally-adapted inbred genotypes. The first experiment comprised F₃ progeny rows, each derived from a single unselected F₂ plant, the second, F₃ bulks selected for resistance, and the third, a comparison of selected and unselected F₂-derived F₄ lines. The number of days to flowering and to maturity, the incidence of mosaic and necrosis symptoms, seed yield and seed size were recorded. There was evidence that late flowering and maturity were associated with BCMV resistance in some crosses, though not strongly enough to present an obstacle to plant breeding. The incidence of virus symptoms and seed yield were influenced by genetic factors additional to the major resistance genes, and variation in seed yield was present not only between bulk populations of crosses, but also between single-row plots of lines within crosses. This indicates that early-generation selection for yield in the presence of BCMV, even among progeny selected for BCMV-resistace, is likely to be effective. However, the variation in yield among F₄ lines was least in the highest-yielding crosses, which may represent a limit to successful selection for yield. Seed size was partly under additive genetic control, but there was also evidence of non-allelic interactions. There was no association between large seed size, preferred by consumers, and susceptibility to BCMV in the progeny, indicating that the association between these characters in the parent lines is fortuitous and will not present an obstacle to plant breeding. It is noted that a considerable amount of useful genetic information can be obtained without recourse to elaborate crossing schemes, provided that unselected progeny are included in experiments as controls. The evidence presented indicates that resistance to BCMV can be combined with appropriate values of maturity date, yield and seed size without the need for backcrossing.     

Identification of quantitative trait loci for grain yield, seed protein concentration and maturity in field pea (Pisum sativum L.)

Breeding efforts to improve grain yield, seed protein concentration and early maturity in pea (Pisum sativum L.) have proven to be difficult. The use of molecular markers will improve our understanding of the genetic factors conditioning these traits and is expected to assist in selection of superior genotypes. This study was conducted to identify genetic loci associated with grain yield, seed protein concentration and early maturity in pea. A population of 88 recombinant inbred lines (RILs) that was developed from a cross between 'Carneval' and 'MP1401' was evaluated at 13 environments across the provinces of Alberta, Manitoba and Saskatchewan, Canada in 1998, 1999 and 2000. A linkage map consisting of 193 AFLPs (amplified fragment length polymorphism), 13 RAPDs (random amplified polymorphic DNA) and one STS (sequence tagged site) marker was used to identify putative quantitative trait loci (QTL) for grain yield, seed protein concentration and early maturity. Four QTL were identified each for grain yield and days to maturity, and three QTL were identified for seed protein concentration. A multiple QTL model for each trait showed that these genomic regions accounted for 39%, 45% and 35% of the total phenotypic variation for grain yield, seed protein concentration and days to maturity, respectively. The consistency of these QTL across environments and their potential for marker-assisted selection are discussed in this report.     

Geneticanalysis of drought stress response in rapeseed (Brassica campestris and B. Napus). II. Yield improvement and the application of selection indices

Summary The expected improvement in grain yield if selection was made for plant characters measured between flowering and maturity was evaluated in populations of rapeseed (Brassica campestris and B. napus) grown in a droughted environment. Drought was commenced at flowering in each species and measurements were made on plants at the commencement of the drought stress, during the stress treatment and at crop maturity.Substantial genetic and phenotypic variation was observed in yield as well as the different morphophysiological determinants of yield. In B. campestris no single parameter was found to be a suitable alternative selection criterion to yield since the correlated responses in yield if selection was for another character was lower than if selection was for yield alone. By the use of a selection index however, joint selection for yield, as well as harvest index, 1000 seed weight and seeds per pod, was expected to be 20% more effective than direct selection for yield under drought. In the B. napus population direct selection for flowering time or for harvest index was predicted to result in a genetic advance in yield equal to or greater than that obtained by direct selection for yield, whereas joint selection for flowering time and yield should result in a 16% greater yield increase. Selection for increased yield in these populations grown in droughted conditions is discussed.     

Recurrent selection for grain yield in early generations of two barley populations

Summary Two spring barley composites, one based on eight West-European two-rowed cultivars (A) and one, the predominantly six-rowed composite XXI, based on several thousands of barley cultivars (B), formed the starting point of a recurrent selection procedure. The aim was to study whether recurrent selection in early generations is an effective procedure to improve barley populations for agronomic characteristics, especially grain yield.After two cycles of recurrent selection in the two populations A and B separately, and consisting of single plant selection followed by line selection, one cycle of recurrent selection was applied to the population produced by intercrossing the selected A and selected B lines.The selection for grain yield in the F2 single plant stages and the F3 line stages was carried out by selecting the plants or lines with the largest mean head weight provided that they did not tiller too poorly. Also some selection was applied against extremes in heading date and against tall plants.After two cycles of recurrent selection the grain yield, tested over two years and two locations, had increased with 16.5% in population A and with 27.0% in population B. Both the single plant selection and the line selection had contributed significantly to this response.The population created by crossing the selected A with the selected B lines showed a significant reduction in yield compared to the mean yield of the A and B lines constituting this population. Single plant selection, followed by line selection did raise the yield level 5.7% above that of the mean of these A and B lines. Several lines produced from this intercross combined an excellent grain yield with outstanding resistance to barley leaf rust and powdery mildew. However, these lines like the entire intercross population suffered from susceptibility to lodging, a characteristic derived from population B.In five experimental situations mixtures of genotypes were compared with the mean of the monocultures of the constituting genotypes. The mixture yielded always more, the average mixture effect being 4.5%.     

Study of heritable variation and genetics of earliness in mungbean (<Emphasis Type="Italic">Vigna radiata</Emphasis> L. Wilczek)

Fifty-five mungbean lines were evaluated for days to maturity and grain yield per plant. This material showed considerable range of variability for the target traits. Eight genetically diverse parents were selected and used for a full diallel set of crosses to study the mode of inheritance for earliness related parameters (days to flowering, days to maturity and length of reproductive phase) during summer 2005. The F₁ generation of these crosses was sown during the spring of 2006 and the selfed seeds were used to raise the F₂ generation during kharif season. The data recorded from two generations were subjected to genetic analysis. The formal ANOVA showed the significance of both additive and dominance effects for all the traits in both generations. Significance of D, H₁ and H₂ components also confirmed the contribution of both additive and dominance effects in controlling the inheritance of these traits. The estimates of narrow sense heritability were low to moderate except higher estimates for days to maturity in F₂ generation, while the broad sense heritability estimates were relatively higher. Seasonal and environmental effects were also found to be significant. In view of the complex nature of gene action for earliness, it is suggested that breeders should look for transgressive recombinants of earliness and other desirable attributes in later segregating generations to gain higher genetic advance. The variety NM92 was found to be the best source of earliness in mungbean breeding.