Showing papers on "Heterosis published in 1985"
TL;DR: A bimodal distribution of outCrossing rates was observed for natural plant populations, with more primarily selfing and primarily outcrossing species, and fewer species with intermediate outcrossed rate than expected by chance.
Abstract: A bimodal distribution of outcrossing rates was observed for natural plant populations, with more primarily selfing and primarily outcrossing species, and fewer species with intermediate outcrossing rate than expected by chance. We suggest that this distribution results from selection for the maintenance of outcrossing in historically large, outcrossing populations with substantial inbreeding depression, and from selection for selfing when increased inbreeding, due to pollinator failure or population bottlenecks, reduces the level of inbreeding depression. Few species or populations are fixed at complete selfing or complete outcrossing. A low level of selfing in primarily outcrossing species is unlikely to be selectively advantageous, but will not reduce inbreeding depression to the level where selfing is selectively favored, particularly if accompanied by reproductive compensation. Similarly, occasional outcrossing in primarily selfing species is unlikely to regularly provide sufficient heterosis to maintain selection for outcrossing through individual selection. Genetic, morphological and ecological constraints may limit the potential for outcrossing rates in selfers to be reduced below some minimum level.
818 citations
TL;DR: A 6 × 6 diallel cross was conducted in spring-planted oilseed rape (Brassica napus L.) in 1983 at Elora and Dundalk, Ontario, and specific combining ability was as important as general combining ability for 1000 seed weight, physiological maturity, plant height, and lodging resistance.
Abstract: A 6 × 6 diallel cross was conducted in spring-planted oilseed rape (Brassica napus L.) in 1983 at Elora and Dundalk, Ontario. The F1 hybrids exhibited positive heterosis for seed yield, of up to 72...
112 citations
TL;DR: Average individual effects indicate that Angus, compared with Hereford, had calves that were born earlier, had lighter birth weights, lower pre- and postweaning gains and lower pregnancy rates.
Abstract: Data from 1,909 purebred, F1, backcross and F2 and F3 inter se combinations of Angus and Hereford were used to estimate average individual, maternal and grandmaternal genetic effects, individual and maternal heterosis, dominance and epistatic genetic effects. Models for evaluating heterosis and epistatic or recombination effects were discussed. Average individual effects indicate that Angus, compared with Hereford, had calves that were born earlier, had lighter birth weights, lower pre- and postweaning gains and lower pregnancy rates. Angus also produced lighter weight carcasses with more fat cover and marbling. Maternal effects of Angus were in the direction of reduced birth weight, greater calving ease, higher preweaning but lower postweaning growth rate and increased fatness when contrasted with Hereford. There was a tendency for opposite direction of maternal and grandmaternal effects for traits influenced by preweaning maternal environment. When additive X additive effects were ignored, total heterosis was significant for earlier day born, heavier birth weight, preweaning and postweaning gain, and heavier and fatter carcasses. Heterosis retained in F3 inter se vs F1 generation crosses indicated that net epistatic effects were relatively negligible for date of calving, birth weight, weaning gain and fat cover. There was a greater reduction of heterosis effects than expected from dominance alone for survival, pregnancy and marbling score. Loss of heterosis in F3 was less than expected for postweaning gain, carcass weight and rib eye area. Except for survival, pregnancy and marbling, these deviations from dominance expectations, or lack of them, are favorable for F3 composite populations.
96 citations
TL;DR: Genetic divergence between the parents had a positive relationship with heterosis and SCA effects of the hybrids of the parents belonging to different groups but not in the same group.
Abstract: Genetic diversity among ten varieties of spring wheat used as parents in a diallel cross was assessed through multivariate analysis (D(2)-statistics) and then related to heterosis and SCA effects of their hybrids. The parents fell into three groups. Group I contained the varieties, 'Nobre', 'Girua' and 'Carazinho'; group II contained 'Sonalika', 'Lyallpur' and 'Pitic 62' and group III contained 'Indus 66', 'Balaka', 'Sonora 64rs and 'MSl'. The varieties of group I were good general combiners, while the varieties of group III were poor combiners. Significant heterotic and SCA effects for yield and yield components were observed in the hybrids of the parents belonging to different groups but not in the same group. Genetic divergence between the parents had a positive relationship with heterosis and SCA effects of the hybrids.
84 citations
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TL;DR: Recombination loss in the F 2 or the mating of similar crosses interse is a function of the recombination fraction between loci, differences in gene frequencies, and additive by additive and dominance by dominance epistatic effects.
59 citations
41 citations
TL;DR: The present results provide evidence that heterozygosis for many genes and gene complexes does produce high fitness without previous selectional coadaptation.
Abstract: The relative viabilities of homozygous and heterozygous karyotypes were measured by making crosses between strains ofD. ananassae homozygous for ST or inverted gene orders in the second and third chromosomes. The strains utilized during the present study originated from widely separated localities in India, Kuala Lumpur and Kota Kinabaru, Malaysia and Chian Mai, Thailand. The presence of heterosis in many interpopulation crosses is evident from the results which show that the inversion heterozygotes formed by chromosomes coming from distant populations exhibit heterosis. On the other hand, heterosis is absent in two intrapopulation crosses. Thus the present results provide evidence that heterozygosis for many genes and gene complexes does produce high fitness without previous selectional coadaptation.
25 citations
TL;DR: The results suggest that, in general, in triticale allelic interactions within the wheat and the rye components are suppressed in favour of intergenomic interactions.
Abstract: Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents as well as the triticale derivatives were then crossed each within the same group of species in all possible combinations. Parents, F1s, and F2 populations were used to study the inheritance of a set of morphological and yield characters. The results suggest that, in general, in triticale allelic interactions within the wheat and the rye components are suppressed in favour of intergenomic interactions. Heterozygosity in the rye genome appeared to be detrimental for triticale, whereas heterozygosity in the wheat genome only resulted in positive interactions between certain characters. The retention of a high level of heterosis for kernels per spike in the F2 generation of such hybrids indicates interactions between genes which are in the homozygous state in the rye but remain in the heterozygous state in the wheat genome. If heterozygosity in the wheat component occurs between genes in the A and B genomes (homoeoalleles), it can be fixed in true breeding lines. This condition may ultimately lead to the fixation of their benefical effect on the interaction between wheat and rye genome. Aneuploidy caused a significant decline in performance for most of the investigated characters.
24 citations
01 Jan 1985
TL;DR: Genetic models are constructed which allow inbreeding depression to change with the mean selfing rate in a population by incorporating both mutation to recessive and partially dominant lethal and sublethal alleles at many loci and mutation in quantitative characters under stabilizing selection.
Abstract: Summary. -The amounts of inbreeding depression upon selfing and of heterosis upon outcrossing determine the strength of selection on the selfing rate in a population when this evolves polygenically by small steps. Genetic models are constructed which allow inbreeding depression to change with the mean selfing rate in a population by incorporating both mutation to recessive and partially dominant lethal and sublethal alleles at many loci and mutation in quantitative characters under stabilizing selection. The models help to explain observations of high inbreeding depression (>50%) upon selfing in primarily outcrossing populations, as well as considerable heterosis upon outcrossing in primarily selfing populations. Predominant selfing and predominant outcrossing are found to be alternative stable states of the mating system in most plant populations. Which of these stable states a species approaches depends on the history of its population structure and the magnitude of effect of genes influencing the selfing rate.
22 citations
21 citations
TL;DR: Data extracted from reports on Bos taurus × Bos indicus crossbreeding were used to estimate the amount of heterosis, and the estimates exceeded their sampling error in three of the four traits, and in all these cases the effect was in the undesirable direction.
TL;DR: To examine the effect of selection for body weight on levels of heterosis for reproductive traits, crosses were made between three groups of six lines of mice, one group unselected (controls) and the other two selected for high (large lines) and low (small lines) 6-week body weight, respectively.
Abstract: To examine the effect of selection for body weight on levels of heterosis for reproductive traits, crosses were made between three groups of six lines of mice, one group unselected (controls) and the other two selected for high (large lines) and low (small lines) 6-week body weight, respectively. The coefficient of inbreeding of each line was about 0.60. In a comparison of purebred and crossbred progeny, both out of purebred mothers, there was on average 4% heterosis for number born, 3% for percentage weaned and 8% for numbers weaned. In a comparison of purebred and crossbred mothers, each mated to males of an unrelated strain and dissected on the 17th day of gestation, crossbreds had on average 1.6 more live embryos, which was 22% of the purebred mean. This comprised an increase of 0.6 corpora lutea, of 0.4 in survival to implantation and of 0.6 in subsequent survival to 17 days. The heterosis was similar whether the mothers had parents of the same or different size.
TL;DR: In this article, a maize (Zea mays L.) inbred line was selected for study and five recessive alleles were selected for this study to ascertain if pleiotropic vigor effects may also be expressed in the heterozygous background of a hybrid.
Abstract: Present knowledge of the control of heterosis and various vigor characteristics on a single gene or locus basis is inadequate. Information on this subject was obtained by producing a number of mutant recessive alleles in a maize (Zea mays L.) inbred line and selecting 31 for study. It was obvious from observation that most of the recessive alleles exhibit numerous pleiotropic effects affecting various vigor characteristics in the homozygous background of the inbred. Five of the recessive alleles were selected for this study to ascertain if pleiotropic vigor effects may also be expressed in the heterozygous background of a hybrid. Each allele produced an array of pleiotropic effects, either positive or negative, affecting various vigor characteristics in the hybrid. Considering pleiotropic effects in the context of single gene differences, the effects on individual vigor characteristics range from small to large. One allele increased the grain yield by three percent. The genetic nature of the pleiotropic effects is not clear at this time; however, it is proposed that pleiotropic effects associated with recessive alleles provide a genetic basis for heterosis.
TL;DR: A representative group of 100 elite lines from 68 crosses made at IRRI and 18 improved varieties were studied, using Mahalonobis, D2-statistic and canonical analysis, to understand the nature and magnitude of divergence and to assess the importance of a set of quantitative characters related to yield in genetic differentiation.
Abstract: A representative group of 100 elite lines, 67 of which are restorers and 33 maintainers, from 68 crosses made at IRRI and 18 improved varieties from five countries were studied, using Mahalonobis, D2-statistic and canonical analysis, to understand the nature and magnitude of divergence and to assess the importance of a set of quantitative characters related to yield in genetic differentiation. The 100 genotypes were grouped into 13 clusters. There were three single variety clusters and the number of lines in the remaining clusters ranged from 2–36. Canonical vector values indicated the importance of yield followed by 1,000-grain weight, days to maturity and plant height in primary as well as in secondary differentiation. Results showed that yield, number of tillers per plant, days to maturity and 1,000-grain weight contributed largely to the divergence. There were no indications of a relationship between geographical diversity and genetic diversity in the present study. Disposition of IRRI developed maintainers and restorers into various clusters indicated the presence of large amounts of diversity within the IRRI elite lines which suggested that these materials could be used in crossing programs to produce heterotic F1 hybrids. Crossing of maintainers and restorers among the highly diverse groups was suggested as it may produce F1S that will give higher magnitudes of heterosis.
Journal Article•
TL;DR: A diallel analysis with eight varieties of rice revealed very poor manifestation of heterosis for kernel length, breadth and length: breadth ratio and a close association between per se performance and gca effects of parents was observed.
Abstract: A diallel analysis with eight varieties of rice (Oryza sativa L.) revealed very poor manifestation of heterosis for kernel length, breadth and length: breadth ratio. The gene action appeared to be additive for kernel length but both additive and non-additive gene actions were found important for kernel-breadth and length: breadth ratio. 'CP 231′ and 'T 9′ were good general combiners for kernel length, breadth and length: breadth ratio. in general, a close association between per se performance and gca effects of parents was observed.
TL;DR: The resemblance of absorption and transport patterns of Zn in CSH‐8 to those of 36‐A strongly suggests that the trait is inherited from the female parent, and significant hybrid vigor was observed in Zn transport from ZnEDDHA for the two hybridsCSH‐7 and CSH-8.
Abstract: Zinc absorption and transport patterns were examined in sorghum and maize hybrids and their parent cultivars with a view to observe, if any, and relate the differences amongst them meaningfully to traits like hybrid vigor. Short term uptake by excised roots or intact seedlings, from different concentrations of ZnCl2 or ZnEDDHA and also, time course from 50 μM ZnCl2, were measured. The results showed significant differences in the Zn absorption patterns by excised roots of sorghum cultivars. The rate of Zn transport to shoot in CSH‐8 was found to be higher than in others. The amount of Zn transported from ZnEDDHA was also more than that from ZnCl2 in all sorghum cultivars. Furthermore, significant hybrid vigor was observed in Zn transport from ZnEDDHA for the two hybrids CSH‐7 and CSH‐8. The resemblance of absorption and transport patterns of Zn in CSH‐8 to those of 36‐A strongly suggests that the trait is inherited from the female parent. No heterosis was observed in the absorption and transport ...
TL;DR: Heterosis was more extensive in crosses involving large or control lines than in crosses with small lines, and there was no detectable heterosis in several measures of developmental rate, such as age at vaginal opening.
Abstract: To examine the effect of selection on levels of heterosis, crosses were made between three groups of six lines of mice, one group unselected (controls) and the other two selected for high (large lines) and low (small lines) 6-week body weight, respectively. The coefficient of inbreeding of each line was about 0.60. Each line was crossed reciprocally to one line from each of the parental groups, as well as producing purebred progeny. Heterosis for 3-week weight, 6-week weight and 3-6 week gain averaged 0.0%, 2.4% and 4.2%, respectively, and was higher for males than for females. Heterosis was more extensive in crosses involving large or control lines than in crosses with small lines. There was no detectable heterosis in several measures of developmental rate, such as age at vaginal opening. Food conversion efficiency and carcass composition were measured on a sample of the animals. Food consumption, gonadal fat pad weight, and hindquarters weight, each expressed as a proportion of body weight, exhibited -4.0%, 5.6%, and 2.3% heterosis, respectively.
TL;DR: Heterosis and inbreeding depression in 13 crosses involving 10 dry bush bean, Phaseolus vulgaris L., lines and varieties are reported for days to maturity, pods per plant, 100-seed weight, seeds per pod, and bean yield.
Abstract: Heterosis and inbreeding depression in 13 crosses involving 10 dry bush bean, Phaseolus vulgaris L., lines and varieties are reported for days to maturity, pods per plant, 100-seed weight, seeds per pod, and bean yield. Six crosses showed positive heterosis (27.8–47.3%) over the mid-parent value for bean yield. Parents in each of these heterotic crosses differed for growth habit, seed size and geographical origin. But none of the F1 hybrids yielded significantly better than the highest yielding parental line. None of the crosses showed heterosis for pods per plant. All significant heterotic values for seeds per pod were negative. For 100-seed weight three crosses, both parents of which had small seeds, showed positive heterosis but one cross which had a significant negative value had one parent with small seeds and the one with large seeds. One heterotic cross each for bean yield and 100-seed weight showed subsequent inbreeding depression. But five crosses for bean yield, and one cross for 100-seed weight...
TL;DR: The agronomic performance of eight triazine-resistant single-cross oilseed rape (B. napus L.) hybrids was evaluated; the yield of most of the hybrids was significantly greater than Atr-Regent; some of the hybirds demonstrated mid- parent heterosis, but none of the eight exhibited high-parent heterosis.
Abstract: The agronomic performance of eight triazine-resistant single-cross oilseed rape (B. napus L.) hybrids was evaluated. The yield of most of the hybrids was significantly greater than Atr-Regent; some of the hybirds demonstrated mid-parent heterosis, but none of the eight exhibited high-parent heterosis. In most cases the hybrids were intermediate to the parents for flowering date, plant height, lodging resistance, physiological maturity, percent oil and percent protein.Key words: Brassica napus L., oilseed rape, F1 hybrid, triazine resistance
TL;DR: Seven highly inbred lines of White Leghorn chickens were used in a near complete diallel mating plan during eight years, showing large differences between line effects could be found in all traits and a negative correlation between reciprocal effects of egg weight and body weight.
Abstract: Seven highly inbred lines of White Leghorn chickens were used in a near complete diallel mating plan during eight years. The lines originated from three different base populations selected for egg weight. Average inbreeding coefficients of parents of chicks hatching in successive years were 0.75, 0.80, 0.84, 0.86, 0.89, 0.91, 0.93 and 0.94. The composition of line, specific combining ability and reciprocal effects and their estimated values are given. These effects were estimated for age at first egg (AFE), average weight of all eggs laid to 40 weeks (EW40), body weight at 40 weeks (BW40), number of eggs to 40 weeks (EP40) and number of eggs between 41 and 60 weeks (EP60). Records of 3247 hens surviving to 40 weeks and of 3133 birds to 60 weeks could be used. Large differences between line effects could be found in all traits. They were only partly due to the preceding selection in the base populations. All specific combining effects were in the expected direction, negative for AFE and positive for EW40, BW40, EP40 and EP60. Recovery of inbreeding depression inflated these effects rather substancially. Average heterosis, defined as the relative superiority of a line combination over the mid parent value, was −11.3%, 5.8%, 7.8%, 45.1% and 35.8% for AFE, EW40, BW40, EP40 and EP60 respectively. One line showed a relative superiority in AFE of -19.3% compared to about −7.9% for all other combinations. Reciprocal or sex-linked effects were generally smaller in all traits than specific combining effects, they were considerably smaller in AFE, EP40 and EP60. General reciprocal effects could be found for several lines in one or more traits. Offspring of two lines, when used as sire lines, showed a negative correlation between reciprocal effects of egg weight and body weight.
TL;DR: In this paper, a newly released F1 hybrid wheat (Hybrid Titan) was compared with its parents and three commercial check cultivars in yield trials over 16 site years, and the authors emphasized the need for both parents to be high-yielding and to have good combining ability for both yield and quality.
Abstract: A newly released F1 hybrid wheat (Hybrid Titan) was compared with its parents and three commercial check cultivars in yield trials over 16 site years. Mid-parent heterosis varied considerably (100-127%) over the sites and averaged 111%. However, high-parent and high-check cultivar heterosis levels were much lower (99-119%), most likely a consequence of the low yield of the male parent. A concurrent seeding rate trial showed that lower levels of heterosis resulted if the seeding rate of the hybrid was reduced below that of the parent and check cultivars. Quality tests performed on the harvested grain showed some characters deviating considerably from expected values. The most significant of these were lower milling yield, flour protein content, and water absorption. The T. timopheevi nucleo-cytoplasmic system for producing hybrid wheat was implicated as having likely side effects on yield performance and quality. The study emphasized the need for both parents to be high-yielding and to have good combining ability for both yield and quality.
TL;DR: Heterosis in vegetative characters changed between anthesis and maturity, which suggests different rates of development in the hybrids and their parents.
TL;DR: The results strongly suggest that recombinant inbred lines, possibly outyielding the better F1's could be produced.
Abstract: SUMMARY
The feasibility of producing commercially acceptable inbred lines of Brussels sprouts is investigated. Two experiments are described which examined the nature and extent of heterosis in this crop using the techniques of biometrical genetics. They indicate incomplete dominance for several production traits, lower F1 uniformity and the presence of inbreds that outyield some F1's. These results strongly suggest that recombinant inbred lines, possibly outyielding the better F1's could be produced. Five crosses were identified for inbreeding by SSD and 1000 lines are being produced from each. The principles upon which these crosses were identified are described.
Journal Article•
TL;DR: Seventy-two Ft hybrids resulting from line (18) × tester (4) matings among 22 hexaploid triticale genotypes were evaluated and it appeared that a specific range of divergence favoured the expression of heterosis for a particular character.
Abstract: Seventy-two Ft hybrids resulting from line (18) × tester (4) matings among 22 hexaploid triticale genotypes were evaluated. Using D'-statistic, 94 progenies were classified into 11 clusters. Correlation coefficients between genetic divergence, as defined by D2 values and mean group distances, heterosis and s.c.a. Were computed for tillers per plant, graing per spike, 1000 grain weight and grain yield per plant. It appeared that neither heterosis nor s.c.a. is a function of genetic divergence. Rather, a specific range of divergence favoured the expression of heterosis for a particular character. Results have been discussed in light of their importance in triticale breeding.
Journal Article•
TL;DR: The investigation indicated the possibility of maximising heterosis for number of grains by identifying parents possessing the highest level of heterotic potential forNumber of ovules and per cent of grain conversion.
Abstract: Heterosis manifest was studied for number of grains in a set of inter-varietal crossess of maize. in parental varieties as well as the crosses the mean-number of grains was considerably less than that of ovules present in the ear. Ear length was not correlated with number of grains per ear, per cent grain conversion and 100 grain weight. The investigation indicated the possibility of maximising heterosis for number of grains by identifying parents possessing the highest level of heterotic potential for number of ovules and per cent of grain conversion.
TL;DR: The strong positive association of callus growth with seed yield indicates the possibility of using this system for mass screening and selection of superior hybrids.
Abstract: Studies on callus growth and shoots/cotyledon, using seven different genotypes of pigeonpea and their hybrid progenies, revealed continuous variation for these traits. Hence, the type of gene action influencing in vitro cell proliferation and differentiation has been investigated in a diallel analysis of seven pigeonpea genotypes. Highly significant average heterosis was recorded for callus growth and seed yield/plant. In general, the F1 hybrids which showed heterosis for callus growth also exceeded their better parent for yield/ plant. Combining ability analysis revealed both additive and non-additive gene effects for callus growth, while number of shoots/cotyledon was mostly governed by non-additive gene effects. The genotype, ‘ICP 7035’, was the best general combiner for callus growth and shoot forming capacity of cotyledons. Two cross combinations, ‘7186’ב6974’ and ‘7035’בT-21’, showed maximum SCA effects for callus growth and shoots/cotyledon. Callus dry weight was positively correlated with seed yield/plant and seedling weight. The strong positive association of callus growth with seed yield indicates the possibility of using this system for mass screening and selection of superior hybrids.
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TL;DR: In a set of crosses involving five tall types of which four were of Russian origin, as male parents and nine genotypes as females, heterosis and combining ability were studied for days to first flowering and days to maturity, while only two crosses showed significant better parent heterosis with respect to days to flowering.
Abstract: In a set of crosses involving five tall types of which four were of Russian origin, as male parents and nine genotypes as females, heterosis and combining ability were studied for days to first flowering and days to maturity. While only two crosses showed significant better parent heterosis with respect to days to flowering, seven crosses showed significant better parent heterosis for days to maturity. Though both additive and non-additive variances were important for days to first flowering, the former was more predominant. For days to maturity, only non-additive variance was significant. Based on g.c.a. effects, BG 203, P 517 and P 10 among lines and NEC 249 among testers were indentified as good combiners for earliness. The implications of these results in deciding upon the breeding strategy for evloving early maturing types are discussed.
Journal Article•
TL;DR: The present investigation was undertaken to study the extent, of heterosis in single and three way crosses in sorghum and the highest heterosis and heterobeltiosis was recorded by 1202A×CK60BX IS-84 and 2219A×36B×IS-84 respectively.
Abstract: The present investigation was undertaken to study the extent, of heterosis in single and three way crosses in sorghum. Four male steriles, viz., CK-60A, 2219A, 36A and 1202A and their maintainers were intemated to produce twelve sterile single crosses. These 12 sterile crosses and 4 male steriles were crossed with five restorers, viz., 285, PD-3-1-11, 168, IS-84 and CS-3541, to produce sixty three way and twenty single crosses. The major contribution towards developmental and yield characters came from the male parents in single and threeway crosses. The performance of three way crosses was at per with single crosses. The grain yield per plant exhibited highest heterotic manifestation in both kinds of hybrids. The highest heterosis and heterobeltiosis was recorded by 1202A×CK60BX IS-84 and 2219A×36B×IS-84 respectively. The females, both A and A×B, exhibited limited diversity for most of the characters. Further evaluation of most heterotic three way crosses for seed production and grain yield stability s suggested.