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1.
Longin CF Utz HF Reif JC Wegenast T Schipprack W Melchinger AE 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2007,115(4):519-527
Early testing prior to doubled haploid (DH) production is a promising approach in hybrid maize breeding. We (1) determined
the optimum allocation of the number of S1 families, DH lines, and test locations for two different breeding schemes, (2) compared the maximum selection gain achievable
under both breeding schemes, and (3) investigated limitations in the current method of DH production. Selection gain was calculated
by numerical integration in two-stage breeding schemes with evaluation of testcross progenies of (1) DH lines in both stages
(DHTC), or (2) S1 families in the first and DH lines within S1 families in the second stage (S1TC-DHTC). Different assumptions were made regarding the budget, variance components, and time of DH production within S1 families. Maximum selection gain in S1TC-DHTC was about 10% larger than in DHTC, indicating the large potential of early testing prior to DH production. The optimum
allocation of test resources in S1TC-DHTC involved similar numbers of test locations and test candidates in both stages resulting in a large optimum number
of S1 families in the first stage and DH lines within the best two S1 families in the second stage. The longer cycle length of S1TC-DHTC can be compensated by haploid induction of individual S1 plants instead of S1 families. However, this reduces selection gain largely due to the current limitations in the DH technique. Substantial increases
in haploid induction and chromosome doubling rates as well as reduction in costs of DH production would allow early testing
of S1 lines and subsequent production and testing of DH lines in a breeding scheme that combines high selection gain with a short
cycle length.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
Wegenast T Longin CF Utz HF Melchinger AE Maurer HP Reif JC 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2008,117(2):251-260
Parental selection influences the gain from selection and the optimum allocation of test resources in breeding programs. We
compared two hybrid maize (Zea mays L.) breeding schemes with evaluation of testcross progenies: (a) doubled haploid (DH) lines in both stages (DHTC) and (b)
S1 families in the first stage and DH lines within S1 families in the second stage (S1TC-DHTC). Our objectives were to (1) determine the optimum allocation regarding the number of crosses, S1 families, DH lines, and test locations, (2) investigate the impact of parental selection on the optimum allocation and selection
gain (ΔG), and (3) compare the maximum ΔG achievable with each breeding scheme. Selection gain was calculated by numerical integration. Different assumptions were
made regarding the budget, variance components, correlation between the mean phenotypic performance of the parents and the
mean genotypic value of the testcross performance of their progenies (ρ
P
), and the composition of the finally selected test candidates. In comparison with randomly chosen crosses, maximum ΔG was largely increased with parental selection in both breeding schemes. With an increasing correlation ρ
P
, this superiority increased strongly, while the optimum number of crosses decreased in favor of an increased number of test
candidates within crosses. Thus, concentration on few crosses among the best parental lines might be a promising approach
for short-term success in advanced cycle breeding. Breeding scheme S1TC-DHTC led to a larger ΔG but had a longer cycle length than DHTC. However, with further improvements in the DH technique and the realization of more
than two generations per year, early testing of S1 families prior to production of DH lines would become very attractive in hybrid maize breeding.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
T. Wegenast and C. F. H. Longin contributed equally to this work. 相似文献
3.
Thilo Wegenast H. Friedrich Utz C. Friedrich H. Longin Hans Peter Maurer Baldev S. Dhillon Albrecht E. Melchinger 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2010,120(4):699-708
In hybrid maize (Zea mays L.) breeding, doubled haploids (DH) are increasingly replacing inbreds developed by recurrent selfing. Doubled haploids may
be developed directly from S0 plants in the parental cross or via S1 families. In both these breeding schemes, we examined 2 two-stage selecting strategies, i.e., considering or ignoring cross
and family structure while selection among and within parental crosses and S1 families. We examined the optimum allocation of resources to maximize the selection gain ΔG and the probability P(q) of identifying the q% best genotypes. Our specific objectives were to (1) determine the optimum number and size of crosses and S1 families, as well as the optimum number of test environments and (2) identify the superior selection strategy. Selection
was based on the evaluation of testcross progenies of (1) DH lines in both stages (DHTC) and (2) S1 families in the first stage and of DH lines within S1 families in the second stage (S1TC-DHTC) with uniform and variable sizes of crosses and S1 families. We developed and employed simulation programs for selection with variable sizes of crosses and S1 families within crosses. The breeding schemes and selection strategies showed similar relative efficiency for both optimization
criteria ΔG and P (0.1%). As compared with DHTC, S1TC-DHTC had larger ΔG and P (0.1%), but a higher standard deviation of ΔG. The superiority of S1TC-DHTC was increased when the selection was done among all DH lines ignoring their cross and family structure and using variable
sizes of crosses and S1 families. In DHTC, the best selection strategy was to ignore cross structures and use uniform size of crosses. 相似文献
4.
Mi X Wegenast T Utz HF Dhillon BS Melchinger AE 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2011,123(1):1-10
With best linear unbiased prediction (BLUP), information from genetically related candidates is combined to obtain more precise
estimates of genotypic values of test candidates and thereby increase progress from selection. We developed and applied theory
and Monte Carlo simulations implementing BLUP in 2 two-stage maize breeding schemes and various selection strategies. Our
objectives were to (1) derive analytical solutions of the mixed model equations under two breeding schemes, (2) determine
the optimum allocation of test resources with BLUP under different assumptions regarding the variance component ratios for
grain yield in maize, (3) compare the progress from selection using BLUP and conventional phenotypic selection based on mean
performance solely of the candidates, and (4) analyze the potential of BLUP for further improving the progress from selection.
The breeding schemes involved selection for testcross performance either of DH lines at both stages (DHTC) or of S1 families at the first stage and DH lines at the second stage (S1TC-DHTC). Our analytical solutions allowed much faster calculations of the optimum allocations and superseded matrix inversions
to solve the mixed model equations. Compared to conventional phenotypic selection, the progress from selection was slightly
higher with BLUP for both optimization criteria, namely the selection gain and the probability to select the best genotypes.
The optimum allocation of test resources in S1TC-DHTC involved ≥10 test locations at both stages, a low number of crosses (≤6) each with 100–300 S1 families at the first stage, and 500–1,000 DH lines at the second stage. In breeding scheme DHTC, the optimum number of test
candidates at the first stage was 5–10 times larger, whereas the number of test locations at the first stage and the number
of test candidates at the second stage were strongly reduced compared to S1TC-DHTC. 相似文献
5.
P. Revilla M. I. Vales R. A. Malvar A. Ordás 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(7):1057-1061
Three cycles of S1 recurrent selection for yield were carried out in two synthetic maize populations, EPS6 from humid Spain and EPS7 from arid
Spain. One-hundred S1 lines were evaluated from each cycle of selection and the ten highest-yielding S1 lines were recombined to produce the next cycle. Changes in variability and genetic distances in two synthetic maize populations,
following three cycles of recurrent selection, recombining ten S1 lines in each cycle, were determined. Isozyme analysis was performed on 125 seedlings per cycle of selection (four cycles
in each of two populations). Regressions of each allozyme frequency on cycles of selection were performed, genetic distances
between populations were determined, and simple correlations between genetic distances and heterosis were calculated. The
average heterozygosity per locus was also calculated for each population. Regression analysis did not reveal any common trend
between EPS6 and EPS7 for changes in allele frequencies presumably due to selection. The number of polymorphic loci, the mean
alleles per locus, and the mean heterozygosity did not show any reduction in variability. Finally, selection did not affect
genetic distances among cycles of selection. The agronomic evaluation of the selection program, after three cycles of selection,
revealed that the genetic variance was not significantly reduced for most traits, and that the heterosis among cycles of selection
of both populations had not changed significantly. The conclusions based on isozyme data supported the deductions made from
agronomic data. Three cycles of selection neither caused relevant changes on variability nor on genetic distance among cycles
of selection of both maize synthetic populations. These data did not indicate any basis for increasing the number of S1 lines recombined for recurrent selection.
Received: 28 April 1997 / Accepted: 23 June 1997 相似文献
6.
R. Bernardo 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,82(1):17-21
Summary In hybrid breeding programs, testcross evaluation of lines can be done during the early stages of selfing (early testing) or delayed until the lines are near-homozygous. To evaluate the usefulness of early testing, the expected genetic and phenotypic correlations between testcross performance at different selfing generations were examined. The genetic correlation (r
GnGn
) between testcross performance of S
n
and S
n
, (n>n) individuals or lines is equal to the square root of the ratio of their testcross genetic variances, and it is a function of the inbreeding coefficients (F) at the two selfing generations, i.e., r
GnGn=[(1+F
n
)/(1+F
n
)]0.5. The genetic correlation between testcross performance of lines and their directly descended homozygous (n=) lines is 0.71 for S1; 0.87 for S2, 0.93 for S3, 0.97 for S4, 0.98 for S5, and 0.99 for S5 lines. The effectiveness of early testing is limited mainly by nongenetic effects. The square root of testcross heritability at generation n sets the upper limit on the correlation between phenotypic value at generation n and genotypic value at homozygosity. The probabilities of correctly retaining S
n
individuals or lines that have superior testcross performance at homozygosity (n=) indicate that early testing should be effective in identifying lines with above- and below-average combining ability. However, the risk of losing lines with superior combining ability is high if strong (best 10%) selection pressure is applied during early testing. If only a small proportion of lines is retained based on testcross performance and/or if the heritability of the trait is low, selfing for two or three generations prior to testcrossing may be desirable to increase the likelihood of retaining lines that perform well at homozygosity. The theoretical results in this study support the testcross evaluation procedures for grain yield used by most maize (Zea mays L.) breeders.A contribution from Limagrain Genetics, a Groupe Limagrain company 相似文献
7.
M. N. Inagaki G. Varughese S. Rajaram M. van Ginkel A. Mujeeb-Kazi 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(4):550-556
Yield performance of each group of ten spring bread wheat lines selected by doubled haploid (DH), single-seed descent (SSD)
and pedigree selection (PS) methods from three F1 crosses was compared with the aim of evaluating the DH method in breeding programs. Populations of 65–97 DH lines and 110
SSD lines per cross were used for selection. PS lines were developed by repeated selections from 1500 F2 plants. Yield evaluation was performed at the F6 generation of SSD and PS lines along with DH lines in a 2-year field experiment. It took only 2 years from the planting of
wheat materials for DH production to the planting of selected DH lines for yield evaluation. There was no significant difference
in grain yield between DH lines and PS lines selected from an F1 cross whose parental varieties were closely related in their pedigrees. In two crosses with low coefficients of parentage
and a large variation in their progenies, grain yield of selected DH lines was significantly lower than those of selected
SSD and PS lines. These results confirm that the DH method can save time in obtaining recombinant inbred lines ready for yield
evaluation. However, a larger DH population is required to achieve the same level of genetic advance with the PS method in
crosses containing greater genetic variation.
Received: 23 December 1997 / Accepted: 12 March 1998 相似文献
8.
Rex Bernardo 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2009,119(2):255-262
Maize (Zea mays L.) doubled haploid lines are typically produced from F1 plants. Studies have suggested that the low frequency of recombinants in doubled haploids may reduce the response to selection.
My objective was to determine if, for sustaining long-term response, doubled haploids should be induced in F1 or F2 plants during maize inbred development. In simulation experiments, I examined the response to multiple cycles of testcross
selection among doubled haploid lines derived from F1 plants (denoted by DH), doubled haploid lines derived from F2 plants (DHF2), and recombinant inbred (RI) lines derived by single-seed descent. For a trait controlled by 100 or more quantitative trait
loci (QTL), the cumulative responses to selection were up to 4–6% larger among DHF2 lines than among DH lines. The cumulative responses were up to 5–8% larger among RI lines than among DH lines. The QTL become
unlinked as the number of QTL in a finite genome decreases, and the responses among RI, DH, and DHF2 lines were equal or nearly equal when only 20 QTL controlled the trait. Metabolic-flux epistasis reduced the differences
in the response among RI, DH, and DHF2 lines. Overall, the results indicated that doubled haploids should be induced from F2 plants rather than from F1 plants. If year-round nurseries are used and new F1 crosses for inbred development are initially created on a speculative basis, the development of doubled haploids from F2 rather than F1 plants should not cause a delay in inbred development. 相似文献
9.
H. A. Eagles A. K. Hardacre 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(4):543-549
Summary A backcross population (NZS1) of maize (Zea mays L.) was produced by crossing a highland Mexican population with the elite Corn Belt Dent synthetic AS3, and then by backcrossing to AS3. S1 lines, S2 lines, and S2 testcrosses with an elite tester were used to compare the means, correlations, genetic variances, and predicted gains from selection of NZS1 and AS3 for grain yield, grain moisture at harvest, root and stalk lodging in a cool, temperate environment in New Zealand. The S1 and S2 lines from NZS1 had lower mean grain yields, higher levels of root lodging and higher mean grain moistures than the S1 and S2 lines from AS3. Mean grain yields of testcrosses of NZS1 and AS3 were similar, but NZS1 testcrosses had higher levels of root lodging. Genotypic variances estimated from S1 and S2 lines were larger for grain yield and root lodging for NZS1, smaller for grain moisture, and similar for stalk lodging. Predicted gains from selection for grain yield using intrapopulation methods based on the additive-genetic variance were larger for NZS1, but predicted gains for testcross selection were similar for the two populations. Lines with high combining ability for grain yield and acceptable grain moisture in combination with the tester occurred in NZS1. Because of the higher additive-genetic variance and the occurrence of lines with high combining ability for grain yield, we concluded that populations including highland Mexican germ plasm should be valuable for recurrent selection programs in New Zealand and in other cool, temperate regions. 相似文献
10.
A western redcedar selection study with self-mating was initiated using an accelerated breeding cycle, such that five generations
were completed in 10 years. Thirty random and 30 selected lines for height, from 15 unrelated full-sib families (S0; inbreeding coefficient F = 0) were the founders for the subsequent selfed lines (S1 to S4; F = 0.5 to 0.9375, respectively). Of the original 60 lines, 50 were still in existence at the S4 generation. Random extinct lines and replacement seedlings resulted either from a lack of mature cones or filled seed, whereas
selected line extinctions and replacements were mostly due to a lack of filled seed. Approximately 47% of parent-trees in
the S4 generation displayed temporal separation of male and female function, as opposed to 7% in the S0. Observed response to selection in height was approximately 21% after four generations. There were no significant reductions
in seed weight or vigor across generations, and these traits were not correlated with selection height. Results are discussed
in relation to the general influences of inbreeding and random genetic drift on response to the selection and incorporation
of selfing into tree-breeding strategies. 相似文献
11.
Fan Z Robbins MD Staub JE 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2006,112(5):843-855
Cucumber (Cucumis sativus L.; 2n=2x=14) has a narrow genetic base, and commercial yield of US processing cucumber has plateaued in the last 15 years. Yield may
be increased by altering plant architecture to produce unique early flowering (days to flower, DTF), female (gynoecious, GYN),
highly branched (multiple lateral branching, MLB), long-fruited (length:diameter ratio, L:D) cultivars with diverse plant
statures. The genetic map position of QTL conditioning these quantitatively inherited yield component traits is known, and
linked molecular markers may have utility in marker-assisted selection (MAS) programs to increase selection efficiency, and
effectiveness. Therefore, a base population (C0), created by intermating four unique but complementary lines, was subjected to three cycles (C1–C3) of phenotypic (PHE) mass selection for DTF, GYN, MLB, and L:D. In tandem, two cycles of marker-assisted backcrossing for
these traits began with selected C2 progeny (C2S) to produce families (F1[i.e., C2S × C2S], and BC1 [i.e., F1 × C2S]) for line extraction, and for comparative analysis of gain from selection by PHE selection, and MAS. Frequencies of marker
loci were used to monitor selection-dependent changes during PHE selection, and MAS. Similar gain from selection was detected
as a result of PHE selection, and MAS for MLB (~0.3 branches/cycle), and L:D (~0.1 unit increase/cycle) with concomitant changes
in frequency at linked marker loci. Although genetic gain was not realized for GYN during PHE selection, the percentage of
female flowers of plants subjected to MAS was increased (5.6–9.8% per cycle) depending upon the BC1 population examined. Selection-dependent changes in frequency were also detected at marker loci linked to female sex expression
during MAS. MAS operated to fix favorable alleles that were not exploited by PHE selection in this population, indicating
that MAS could be applied for altering plant architecture in cucumber to improve its yield potential.
The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper
therefore must be hereby, marked advertisement solely to indicate this fact. Mention of a trade name, proprietary product,
or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion
of other products that may be suitable. 相似文献
12.
S. K. St.Martin 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,72(5):682-688
Summary The objective of this study was to compare several selection procedures with respect to expected genetic gain in the population hybrid across a range of initial allelic frequencies, degrees of dominance, and environmental variances. The methods compared were intrapopulation recurrent selection using full-sib or S1 families, full-sib and two half-sib reciprocal recurrent selection procedures, and convergent improvement applied to populations. Comparisons were made by calculating expected allelic frequency changes for each method. The optimal selection method for a given set of allelic frequencies and degree of dominance depended little on the environmental variance. Partly because of its short cycle, full-sib intrapopulation selection was the most effective method for the majority of allelic frequency combinations when the degree of dominance was small and an off-season nursery could be used to make recombinations. With larger values for the degree of dominance, S1 and reciprocal full-sib methods became optimal, the former method especially when favorable alleles had a high frequency and the latter when populations were highly divergent. When off-season nursery use was restricted to making self-pollinations or was absent, S1 selection was optimal for the majority of allelic frequency combinations. Convergent improvement was superior only for extremely divergent allelic frequencies and then only when the degree of dominance was less than 0.10. Half-sib reciprocal methods were never optimal, although the gain for the standard half-sib reciprocal procedure differed little from that of full-sib reciprocal selection when the degree of dominance was 0.75. 相似文献
13.
A. Gallais 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,81(4):493-503
Summary A model to study genetic effects at the level of a population of testcross progenies is presented. As there is no dominance for the testcross value, with the restriction of epistasis to pairs of loci, only additive x additive epistasis can contribute to the variance among progenies. To estimate the variance among progenies due to epistasis, it is necessary to have the population structured in families of full sibs, half sibs or S1, with only a few plants per family tested in combination with the tester. Using a two-way mating design to produce the families, it is possible to estimate the variance due to additive x additive epistasis. The consequence of the presence of epistasis is studied at the level of recurrent selection for combining ability with the tester. It seems that epistasis itself does not change the efficiency of the breeding methods considered. However, when the population from intercrossing is structured in families, it could be efficient to use a combined selection when the heritability is very low. In this case it would be efficient to produce full-sib families (by single-pair matings) at the level of intercrossing. The best procedure is to produce such families at the same time as crossing with the tester. In comparison to the classical scheme of selection for combining ability with a tester, such a modification increases the efficiency of selection 41.1% if an off-season generation can be used. 相似文献
14.
G. Sills J. Nienhuis 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(1-2):275-282
Recurrent selection for specific combining ability (RS-SCA) and S1 family performance (RS-S1) were compared in replicated
selection programs initiated from a common C0 base population of Arabidopsis. Three cycles of selection for aerial biomass were completed in each of two replicate programs of each selection method.
Response to selection was measured on the basis of per se, S1 progeny, and testcross performance with a common tester. All
selection programs improved testcross performance. Testcross gain per cycle in RS-S1 (7.15% cycle-1) and RS-SCA (5.31% cycle-1) were not significantly different. Performance of S1 progeny and populations per se significantly improved over cycles of
selection using RS-S1 but were unchanged by RS-SCA. Codominant molecular marker-allele frequencies were recorded for each
population at 22 polymorphic loci. Trends in marker-allele frequencies were tested by linear regression. Significant trends
in marker-allele frequencies pooled over replicate programs were detected at 8 and 7 loci in the RS-S1 and RS-SCA programs,
respectively. Marker alleles at 2 loci significantly changed frequency in response to both RS-S1 and RS-SCA programs. Marker
alleles at 6 loci significantly changed frequency only in response to RS-SCA. Marker alleles at 6 other loci showed significant
linear trends pooled over replicates only in RS-S1. No markers revealed increases in the frequency of different marker alleles
within loci using the two selection methods. Possible genetic causes of marker frequency changes are discussed, as well as
breeding implications. 相似文献
15.
J. Moreno-González A. R. Hallauer 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1982,61(4):353-358
Summary A method (CRRS) that combines S2 and crossbred family selection in full-sib reciprocal recurrent selection (FSRRS) is proposed. The method requires four generations per cycle in single-eared maize populations. Selection is based on performance of S2 and full-sib families by applying selection index theory. Equations to estimate the coefficients included in the index are given. These estimates are functions of the genetic and phenotypic variances and covariances among and between the two kinds of families. Comparisons of FSRRS and CRRS under equivalent amount of effort show that CRRS has some advantage over FSRRS for low heritability of the trait being selected (e.g., maize yield) and when only one or two locations with two replications are involved in the selection experiment.Joint contribution: Institute Nacional de Investigaciones Agrarias, La Coruna, Spain; and Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Journal Paper No. J-10118 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. Project 2194 相似文献
16.
Flachenecker C Frisch M Falke KC Melchinger AE 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2006,113(6):1113-1120
Selection response of a modified recurrent full-sib (FS) selection scheme conducted in two European flint F2 maize (Zea mays L.) populations was re-evaluated. Our objectives were to (1) determine the selection response for per se and testcross performance in both populations and (2) separate genetic effects due to selection from those due to random genetic drift. Modified recurrent FS selection was conducted at three locations using an effective population size N
e = 32 and a selection rate of 25% for a selection index, based on grain yield and grain moisture. Recombination was performed according to a pseudo-factorial mating scheme. Selection response was assessed using a population diallel including the source population and advanced selection cycles, as well as testcrosses with unrelatesd inbred line testers and the parental F1 generation. Selection response per cycle was significant for grain yield and grain moisture in both populations. Effects of random genetic drift caused only a small reduction in the selection response. No significant selection response was observed for testcrosses, suggesting that for heterotic traits, such as grain yield, a high frequency of favorable alleles in the elite tester masked the effects of genes segregating in the populations. We conclude that our modified recurrent FS selection is an alternative to other commonly applied intrapopulation recurrent selection schemes, and some of its features may also be useful for increasing the efficiency of interpopulation recurrent selection programs. 相似文献
17.
C. Scotti F. Pupilli S. Salvi S. Arcioni 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,101(1-2):120-125
The effect of selfing on vigour and heterozygosity was analysed in six independent families obtained by recurrent cycles of
self-fertilization and selection until the S3 generation. The heterozygosity level, estimated by means of 11 homologous probes, decreased from the S0 to S3 generations and was partially restored in S2×S2 polycrosses. The decreasing trend was influenced by the inbreeding level of the chosen mother plant in each self generation
to advance in subsequent selfing. Plant vigour estimated by Dry Matter Yield (DMY) decreased during inbreeding, and phenotypic
selection of S2 individuals seemed to prove effective as the differences in DMY between vigorous and weak plants were maintained in S2×S2 crosses. No correlation between plant vigour and heterozygosity was found between subgroups of vigorous and weak plants selected
within the same S2 family. Results are discussed with a view to selecting the best performing and least heterozygous plants during inbreeding
to isolate useful genes and linkats in superior partially inbred parental lines.
Received: 4 August 1999 / Accepted: 6 December 1999 相似文献
18.
S. J. Knapp W. C. Bridges Jr. D. Birkes 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(5):583-592
Summary High-density restriction fragment length polymorphism (RFLP) and allozyme linkage maps have been developed in several plant species. These maps make it technically feasible to map quantitative trait loci (QTL) using methods based on flanking marker genetic models. In this paper, we describe flanking marker models for doubled haploid (DH), recombinant inbred (RI), backcross (BC), F1 testcross (F1TC), DH testcross (DHTC), recombinant inbred testcross (RITC), F2, and F3 progeny. These models are functions of the means of quantitative trait locus genotypes and recombination frequencies between marker and quantitative trait loci. In addition to the genetic models, we describe maximum likelihood methods for estimating these parameters using linear, nonlinear, and univariate or multivariate normal distribution mixture models. We defined recombination frequency estimators for backcross and F2 progeny group genetic models using the parameters of linear models. In addition, we found a genetically unbiased estimator of the QTL heterozygote mean using a linear function of marker means. In nonlinear models, recombination frequencies are estimated less efficiently than the means of quantitative trait locus genotypes. Recombination frequency estimation efficiency decreases as the distance between markers decreases, because the number of progeny in recombinant marker classes decreases. Mean estimation efficiency is nearly equal for these methods. 相似文献
19.
Confirmation of QTL controlling seed yield in spring canola (Brassica napus L.) hybrids 总被引:1,自引:0,他引:1
Quijada Pablo A. Maureira Ivan J. Osborn Thomas C. 《Molecular breeding : new strategies in plant improvement》2004,13(2):193-200
Allelic effects observed in QTL discovery experiments must be confirmed to be useful in subsequent breeding efforts. Two QTL affecting seed yield of spring hybrid canola (Brassica napus L.) were previously identified in two populations of inbred backcross lines (IBLs) containing germplasm introgressed from a winter cultivar. The effects of favorable alleles at these QTL were retested by crossing two selected IBLs (M5 and M31) to three spring canola lines having different genetic backgrounds. Doubled haploid (DH) lines derived from each F1 were genotyped with RFLP markers flanking the QTL and grouped into the four possible QTL genotypes. For the first field experiment, DH lines derived by crossing the M5 line to one spring line were crossed to two female testers and evaluated as individual testcross progenies in one environment. QTL genotypes had large variances and were not significantly different. A second field experiment was conducted using the DH lines from the first experiment and two other sets of DH lines derived from the M31 line crossed to two different spring canola lines. Individual lines within each QTL genotype of each set were bulked and crossed to the same testers used in Experiment 1. Bulked hybrid seeds of each QTL genotype were planted in a split-split plot randomized block design and 12 replicates. QTL genotypes had smaller variances in this experiment, and the effects of one QTL were confirmed in some genetic backgrounds. These results suggest that bulking of QTL genotypes and use of an appropriate experimental design with many replicates are needed to detect small differences between QTL genotypes. 相似文献
20.
J. Crossa C. O. Gardner 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(1):33-38
Summary The maize (Zea mays L.) improvement program of the International Maize and Wheat Improvement Center (CIMMYT) develops broad-based maize populations and, until recently, improved all of them through full-sib family selection with international testing. The purpose of this study was to estimate the genetic and genetic × environment variance components for ten of those populations and to measure expected yield improvement from full-sib selection. Mean yield ranged from 3.35–6.81 t ha–1. For five populations the average yield in the last cycle was higher than in the initial cycles. Several populations showed no improvement or yielded less in the final cycle of selection, either because selection intensity was low or because strong selection pressure was applied simultaneously for several traits. Variation resulting from differences among family means within cycles and from interaction between families and locations within cycles were significant in all populations and cycles. Results indicate that variability among full-sib families was maintained throughout the cycles for all populations. The large
ge
2
/
g
2
ratio shown by most populations suggests that yield response per cycle could be maximized if the environments in which progenies are tested were subdivided and classified into similar subsets. The proportion of the predicted response realized in improved yield varied for each population.Journal Paper No. 8640, Nebraska Agric. Res. Div. Project No. 12-159. Research was supported in part by USAID/USDA/ CSRS Research Grant No. 86-CRSR-2-2789 相似文献