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1.
A. Gallais 《Euphytica》1988,39(2):95-104
Summary To discuss the utilisation of heterosis in plant breeding it is necessary to consider its genetic basis. In cross fertilized plants in which the phenomenon of heterosis is very important, such as maize, it appears that a great part can be explained by the mutation load. However in both autogamous or allogamous plants it is difficult to exclude a role of marginal overdominance which could justify hybrid variety production.To know in a relatively short time whether it will be better to develop lines or hybrids it is necessary to know the parameters (mean and variance) of the distribution of all varieties of a given type which can be derived from the breeding population. A numerical application allows the determination of the situations where the best single crosses will be better than the best lines. With some approximate values of the necessary parameters, the case of grain yield in maize and in wheat is briefly discussed.To develop lines or hybrids, a general strategy is given. Its main axis is population improvement which has to be adapted to the type of varieties to develop. It is shown that according to the situation the type of varieties to develop can change with time: single crosses can be more justified at the beginning and lines can be justified later if all heterosis were fixable. To develop hybrids the best scheme is reciprocal recurrent selection with half-sib or full-sib progenies followed by pedigree reciprocal selection initiated by full-sib progeny tests. With this strategy there is no problem of the prediction of hybrid performances. However it seems possible to develop some predictors of heterosis or of specific combining ability between two lines using some criteria of genetic distances. Preliminary results with distances computed from the behaviour of lines in a two-tester top cross design appears very stimulating.Communication given at the206th meeting of teh Genetical Society of Grain Britain 相似文献
2.
A. Gallais 《Plant Breeding》1989,103(4):265-269
With the assumption of biallelism it is shown that differences in line values of genotypes from a random mating population can be predicted by the differences of values in top cross progenies with a heterozygous tester. This prediction is also valid in the case of multiallelism with a constant degree of dominance for each pair of alleles and if the tester is heterozygous for the more “distant” alleles. With an arbitrary tester, the efficiency of the prediction is affected by the proportion of the loci which are heterozygous for the more distant alleles. However, with the assumptions considered on multiallelism, with partial to complete dominance, the correlation between line value and combining ability with the tester is expected to be high for a large range of the repartition ot the loci. A two tester top cross design using highly complementary lines, could also be used. 相似文献
3.
J. Bordes G. Charmet R. Dumas de Vaulx A. Lapierre M. Pollacsek M. Beckert A. Gallais 《Euphytica》2007,154(1-2):41-51
Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance.
DH and single-seed descent (SSD) lines were produced from random S1 progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three
population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the
genetic variance of S1 families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance
of S1 families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all
traits, heritability of SSD or DH lines was higher than heritability of S1 families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S1 testcross progenies and DH or SSD testcross progenies, meaning that the S1 testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation
in DH lines appeared to be more in accordance with the observed variation among S1 families than with the observed variation among SSD lines. 相似文献
4.
Summary Six lines of Pisum were tested in vitro for their ability to produce somatic embryos from apices. Significant quantitative variation was observed. Inheritance of the ability to form somatic embryos was studied using a diallel cross among six different lines. About 80% of the observed genotypic variation was due to additive effects. There is a tendency for the favourable genes to be recessive. It appears that there are two genetic systems involved. Analysis of the distribution of F3 families means from a cross among two extreme lines seems to indicate the presence of a few major genes in the control of somatic embryogenesis of pea. 相似文献
5.
Guylaine Blanc Alain Charcosset Jean-Baptiste Veyrieras André Gallais Laurence Moreau 《Euphytica》2008,161(1-2):71-84
Many studies already investigated marker-assisted selection (MAS) efficiency but mainly in biparental populations. Connected
multiparental populations address a broader diversity and confer a gain of power for QTL detection which must be beneficial
for MAS. Our objective was to compare multiparental connected designs to biparental populations taken separately for MAS and
phenotypic selection. We first detected QTL for flowering time and grain yield in an experimental maize design involving four
parental inbred lines crossed to produce six different biparental populations and confirmed the advantage of multiparental
connected designs over biparental populations for QTL detection. Based on these results we performed stochastic simulations
to evaluate the expected efficiency of four generations of MAS and phenotypic selection. Different parameters were considered:
trait heritability, genetic architecture and whether QTL were assumed to be known or have to be detected. Genetic gains were
higher in the multiparental design than on average over the biparental populations considered separately, especially when
favourable alleles were equally distributed among parental lines. When QTL detection was included in the simulation process,
we found that type I error risk considered for declaring QTL as significant should be adapted to the design. Type I error
risks leading to the best response were higher for the biparental populations than for the multiparental design. Besides addressing
a broader diversity, multiparental designs increase the power of QTL detection, which reinforces their superiority over biparental
designs for MAS. Application of MAS to multiparental designs therefore appears promising to accelerate genetic gain in plant
breeding programs. 相似文献
6.
7.
A. Gallais 《Euphytica》1990,48(3):197-209
Summary The concepts of varietal ability and value in test of a genotype or group of genotypes are specified according to the type of variety (clones, hybrids, lines, synthetics) and the testing system (phenotype, S1, General combining ability (GCA), line value, General synthesizing ability (GSA)). Varietal ability and value in test are to be considered as any quantitative characters for which it is possible to define additive effects, dominance effects and epistasis. For diploids in recurrent selection, only additive effects and additive× additive epistasis for varietal value contribute to genetic advance. Genetic advance depends on the covariance between the testing value of the parents and the test value of the progeny by intercrossing. Such a parent-offspring covariance is, in the absence of epistasis and inbreeding, one half of the covariance between additive effects in test of the parents and additive effects in test of their progenies. This allows one to express directly the genetic advance in varietal value according to the type of variety and to the testing system used in recurrent selection. The case of biallelic populations is considered; it allows some discussions on the relative values of components of variance of varietal and test values. 相似文献
8.
A. Gallais 《Plant Breeding》1991,107(4):265-274
Three or four-way recurrent selection is proposed for the development of three or four-way crosses. In term of genetic effects, it could be justified if there are interactions between more than three genes, whether alleles or not, if autopolyploids are also considered. For autotetraploids, in particular with tetragenic interaction, four-way recurrent selection could be more effective than reciprocal recurrent selection (two-way selection). According to the types of progenies used to develop the tests, different selection procedures are considered, the two extremes being called method 1 and method 3. With method 1 (selection for three or four-way general combining ability) a plant from a population is used to produce three-way or four-way progenies with the other populations used as testers. With method 3 (selection for three or four-way specific combining ability) three-way or four-way crosses are developed with one plant from each population. To study the genetic advance, the theory is developed to consider either diploidy or autotetraploidy. It is shown that method 3 will allow a greater genetic advance than method 1 for low heritability and low selection intensity. The way towards hybrid development with three and four-way pedigree selection is discussed: again selection can be for general or specific three or four-way combining ability. It is emphasized that an advantage of recurrent selection for three or four-way specific combining ability is that it allows direct varietal development with pedigree selection on three or four-way specific combining ability. Some other practical aspects are also considered. 相似文献
9.
Summary Thirty lines of pea were tested in vitro to evaluate their ability to produce somatic embryos. Three distinct genotypic classes were detected (strong, medium and weak). The best responses were obtained in Pisum sativum. Abnormal somatic embryos and secondary embryogenesis seem to constitute the principal obstacle to the development of these structures. 相似文献
10.
A program was initiated in 1994 to compare the efficiency of marker-assisted selection (MAS) and conventional phenotypic selection.
A population of 300 F3:4 families was generated from the cross between two maize inbred lines F2 and F252 and selected on an index combining grain yield and grain moisture at harvest. This population was characterised for 93 RFLP
markers and evaluated as testcrosses in a large range of environments. Three methods of selection were applied (i) two cycles
of conventional phenotypic selection; (ii) two cycles of MAS based on an index combining phenotypic values and QTL genetic
values and (iii) one cycle of combined MAS followed by two cycles of selection based only on the QTL effects estimated in
the first generation. The different populations were characterised for RFLP markers. The evolution of allele frequencies showed
that selection on only-markers was very efficient for fixing QTL alleles found favourable in the initial population. This
evolution was quite different from that observed for phenotypic selection or combined MAS. Genetic gain was evaluated and
found significant for each method of selection. Nevertheless, the difference between phenotypic selection and combined MAS
was not significant. The two additional cycles of MAS on only-markers did not improve significantly the genetic value of the
population. Moreover, the genetic variance of this population remained high, despite most of the QTL initially detected were
almost fixed. The results suggest that the QTL effects estimated in the initial population were not stable due to epistasis
and/or QTL by environment interactions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献