Showing papers on "Heterosis published in 1987"

Inheritance of aluminum tolerance in maize

Abstract: The inheritance of Al tolerance in maize (Zea mays L.) was studied in nutrient solution. Analysis of relative seminal root lengths of six generations (P1, P2, F1, F2, BC1, and BC2) derived from crosses between tolerant and non-tolerant inbred lines showed that additive gene effects contributed most to genetic variation for Al tolerance of the materials included in this study. Dominance effects accounted for only half as much variation as did additive effects. Effects of epistasis contributed little compared to other gene effects. The frequency distributions of plants within the F2 generations were continuous, unimodal, and typical for quantitatively inherited traits. There was some tendency for non-tolerance to be dominant over tolerance, but it was not consistent. In a diallel cross among inbred lines, the analysis of F1 crosses indicated that the variance for general combining ability explained most of the variation, but specific combining ability was statistically significant in each case.

Heterosis among populations of maize (Zea mays L.) with different levels of exotic germplasm.

Abstract: Thirteen maize (Zea mays L.) populations including five adapted, five adapted x exotic, two composites of adapted and exotic, and one exotic selected for adaptability were crossed in a diallel mating system. The parents and 78 crosses and nine check hybrids were evaluated for grain yield and plant height in five environments. The Gardner-Eberhart model Analysis II indicated that additive and nonadditive gene effects accounted for 60 and 40% of the total variation among populations, respectively, for grain yield and 86% and 14% of the total variation, respectively, for plant height. Components of heterosis were significant in the combined analysis for both traits. Adapted Corn Belt populations tended to have higher performance in crosses and greater values of variety heterosis than 50% adapted populations. ‘Nebraska Elite Composite’, ‘Corn Belt’ x ‘Mexican’, and ‘Corn Belt’ x ‘Brazilian’ showed high mean yields in crosses, however, they were not among those with high estimates of variety heterosis. One exotic population (‘Tuxpeno’ x ‘Antigua Grupo 2’) and three adapted populations [‘307 Composite’, ‘NB(S1)C-3’, and ‘NK(S1)C-3’] might be combined together to form a high-yielding population. It may be possible to synthesize two useful populations for reciprocal recurrent selection by grouping ‘Tuxpeno’ x ‘Antiqua Grupo 2’, ‘NB(S1)C-3’, and ‘NS(FS)LFW-8’ into one population and ‘NK(S1)C-3’, ‘Krug’x‘Tabloncillo’, and ‘307 Composite’ in the other one.

Dominance is not necessary for heterosis: a two-locus model

Abstract: Under a two-locus model with additive genes which combine multiplicatively to determine a quantitative trait, heterosis is generally observed in the F 1 It is positive only if both frequencies of the best allele at each locus are not higher in the same parental population In the F 2 , heterosis depends on the rate of recombination between the two loci If linkage is tight, F 1 superiority is nearly halved in the F 2 But if the two genes are independent, heterosis is maintained in the F 2 at the same level as in the F 1

Dominance and epistasis in heterosis of white leghorn strain crosses

Abstract: Four unrelated pure strains of White Leghorns including a grandparent strain from industry and 12 two-strain, 24 three-strain, 24 four-strain and 12 F2 strain crosses produced contemporaneously were used to examine the role of dominance and epistasis in heterosis. A control strain and a commercial strain were also included. For egg weight, the heterosis observed closely approximated that expected due to dominance alone. For sexual maturity and body weight, dominance was the major component of heterosis, but epistasis made a significant contribution — additive by additive (A × A) genetic effects for sexual maturity and 140-d body weight, and parental epistasis for mature body weight. Both dominance and epistasis played a significant role in heterosis for egg production traits. A × A, dominance by dominance (D × D) and additive by dominance (A × D) epistasis were all important for hen-housed egg production and hen-housed egg yield. For hen-day rate of egg production, A × A epistasis was significant only ear...

Genetic and non-genetic factors affecting anther culture of Brussels sprouts (Brassica oleracea var. gemmifera).

Abstract: Eight inbred lines of Brussels sprouts and ten F1 hybrids derived from them were tested for their response to anther culture. From 5–19 plants per genotype were tested, and each plant was tested on 3–6 separate occasions. Results from the inbred lines were broadly similar to those from the F1 hybrids, despite the inbreds producing fewer buds and having a higher frequency of anther deformities. The maximum embryo yield from an inbred line was 215 embryos per 100 anthers, and from a hybrid was 275. From estimation of the variance components it was calculated that, for both inbreds and hybrids, about half the total variation was genetic whereas variation due to plants within genotypes and to occasions within plants were each about 13% of the total. The narrow sense heritability of responsiveness to anther culture (estimated by the proportion of variation between inbred lines which was genetic) was 0.48, and there was partial dominance for this character. In three cases the hybrid outyielded the better inbred, and this heterosis may well be due to dispersed dominant genes.

Allozyme heterosis in radiata pine is poorly explained by overdominance

Abstract: Heterosis, the superior vegetative or reproductive vigor associated with heterozygosity, has been observed for allozymes in a wide variety of plant and animal taxa. Its causes, however, are widely debated. To gain insight into the causes of heterosis, we examined the relationship of allozyme heterozygosity and growth rate in a sample from a natural population of radiata pine. Some 244 clones derived from 30 natural stands were grown for 14 yr in an experimental plantation. Height, diameter, and crown growth rates were determined for six to nine ramets per clone; clonal genotypes were scored at 27 polymorphic allozyme loci. Levels of heterozygosity well below average were associated with depressed growth rates. The strength of heterosis within stands was positively associated with the estimated level of natural inbreeding and negatively associated with mean observed heterozygosity. Heterosis varied sporadically among loci and was unrelated to their levels of polymorphism, thus failing to support the hypoth...

Individual Heterosis and Breed Effects for Postweaning Performance and Carcass Traits in Four Breeds of Swine

Abstract: Individual heterosis and direct and maternal breed effects for postweaning average daily gain (ADG), off-test age (AGE) and probed backfat thickness (BF) were estimated from data on 1,664 pigs produced in a complete diallel mating system involving the Duroc, Yorkshire, Landrace and Spotted breeds. The same genetic parameters were estimated for various carcass traits by analyses of data collected on 269 barrow carcasses. Significant breed • environment (i.e., year-season farrowed, parity and sex) interactions were found for ADG, AGE and BF. Specific heterosis estimates for ADG and AGE were all highly significant and reasonably consistent among crosses. Overall heterosis for BF was significant, although specific estimates were not. Overall heterosis estimates were .07 kg/d (10.5%) for ADG, --14 d (7.5%) for AGE and .83 mm (3.2%) for BF. Of 72 specific heterosis estimates for carcass traits, only seven were significantly different from zero, apparendy at random. Durocand Spotted-sired pigs grew faster and were younger off-test than Yorkshireand Landrace-sired pigs. Landrace-sired pigs had higher BF and Duroc-sired pigs lower BF than Spottedor Yorkshire-sired pigs. Breed-of-dam effects for ADG were similar to breedof-sire effects. Significant breed-of-sire effects for carcass traits reflected the superiority of Durocsired pigs for carcass backfat, loin muscle area, lean cuts yield and muscle quality (marbling and firmness). Maternal effects were important for carcass composition in crosses involving the Duroc. Such crosses produced leaner, more heavily muscled carcasses where the Yorkshire, Landrace and Spotted were used as the dam breed. (

Physiological reasons for heterosis in growth of Bos indicus × Bos taurus

Abstract: By comparing growth rates of Brahman (B), Hereford × Shorthorn (HS), their reciprocal F1, hybrid (F1BX), their Fn hybrid (FnBX) and an F1 Charolais × Brahman hybrid (Fl CH x B) in environments that differed in their levels of stresses that affected growth, it was shown that heterosis for growth realized in any environment arose because of heterosis in its underlying determinants, namely growth potential and resistance to environmental stresses. Growth potential of the F1 BX was similar to that of the better parent (HS) whilst resistance to environmental stresses was similar to or approached that of the more resistant parent (B). This combination of high growth potential and high resistance to environmental stresses enabled the F1 BX to outgain both parents at all levels of environmental stress above zero. However, some or all of the heterosis in both growth potential and resistance to environmental stresses was lost in the Fn BX. Thus, although previous selection for increased live-weight gain should have favoured the Fn BX, they realized lower live-weight gains than the Fl BX in all environments and lower live-weight gains than the parental breeds in all but intermediate environments.Because the breeds differed in both determinants of growth, the magnitude of estimates of heterosis for realized growth was dependent on the environment in which it was measured. A figure depicting this interaction was constructed.Comparative estimates were also made of the rate of approach to sexual maturity of bulls of each breed. The F1 BX had similar values to the better parent (HS) for both scrotal circumference and plasma testosterone concentrations. However, the Fn BX had values that were intermediate to those of the parental breeds.Generally, gains of the -F, CH × B exceeded those of all other breeds in all environments but their rate of approach to sexual maturity was slower than that of the F1 BX.

Heterosis and genetic distance in rapeseed (Brassica napus L.): use of kinship coefficient

Abstract: Different agronomic characters have been measured on F1 rapeseeds from inbred lines that are more or less related and on their parents, in Rennes (France). Two different experiments were conducted over a 2-year period. A study of the relationship between heterosis and genetic distance, measured here by a function of kinship coefficient (1–ψ), was carried out in two steps. First, four classes of increasing 1–ψ values were defined and related to heterosis value and F1 performance. The results point out a significant effect of the class, whatever the character and the year. Moreover, the best heterotic hybrids were always obtained with lines unrelated and coming from two different geographic pools. Then, the efficiency of 1–ψ for predicting heterosis or cross values was tested: it varies with year and character. For example, in the first experiment average relationship between lines was high, about 50% of seed yield variation owing to mean parent heterosis was explained with the 1–ψ distance. Key words: hete...

The crossbred sire: experimental results for sheep.

Abstract: Crossbreeding of sheep is practiced to exploit simultaneously the use of additive and nonadditive genetic effects. The goal is to achieve optimal levels of performance appropriate for defined systems of sheep production and marketing. Although the beneficial effects of individual and maternal heterosis on sheep production have been well documented and widely implemented, considerably less is known about the effects of paternal heterosis. Limited evidence suggests that crossbred rams are more sexually aggressive and exhibit greater testicular growth than do purebred rams. Average estimates of paternal heterosis effects were 1.4, -.7 and 2.3% for seasonal fertility, prolificacy and preweaning survival, respectively. The average effect of paternal heterosis on fertility during spring breeding was 29.5%. Progeny of crossbred and purebred sires were similar in birth weight, weaning weight and postweaning growth rate and in phenotypic variation for these growth traits. However, favorable paternal heterosis effects need not exist to warrant the use of crossbred sires. Composite or F1 sires can be used as an effective method to manage the composition of additive breed effects. For example, varying proportions of germ plasm from highly prolific breeds such as the Finnsheep and Romanov can be realized through the use of crossbred sires to set reproductive rates at desired levels. Crossbred sires may be used to a greater extent to optimize additive breed effects than to exploit effects of paternal heterosis. The role of composite breeds in managing both additive and nonadditive effects is discussed.

Heterosis and Additive Breed Effects on Feedlot and Carcass Traits from Crossing Angus and Brown Swiss

Abstract: vi

Heterosis and Combining Ability Analysis in Chilli

Abstract: Four chilli lines, Jwala, Pant C-l, CA 33 and CA 23, were crossed in a half diallel to estimate heterosis and combining ability. Involvement of both additive and nonadditive gene actions was detected for the control of plant height, primary branches/plant, leaf laminar length, fruit length, and days to flower. Out of six hybrids, four exhibited significant relative heterosis for plant height and one for fruit length. Taking into consideration the per se performance, heterosis and sca effect, Jwala × Plant C-1 was the best hybrid, yielding 201 g/plant, followed by Jwala × CA 23 (160g/plant). All the hybrids were earlier than the midparents of which three were even earlier than the early parents.

The crossbred sire: theory.

Abstract: Favorable effects of heterosis on performance of the crossbred market animal and the crossbred dam have been well documented and breeding plans have been developed to utilize these effects. However, a similar mandate for use of the crossbred sire does not exist. Given the common developmental factors involved in reproduction in both sexes, it appears likely that the same nonadditive effects that lead to improved reproductive fitness in the female would also have an effect in the male. Most studies that have evaluated heterotic effects in the male have observed heterosis for at least some components of male reproduction, but have been unable to document consistently favorable effects of the crossbred male on overall conception rate. This result may reflect the categorical nature of conception and possible limiting effects of the female on expression of male differences. Important effects of true paternal heterosis, parallel to maternal heterotic effects acting through the maternal environment provided by the dam, appear unlikely because of the less-intimate relationship between offspring and sire. However, if the relationship between underlying breeding value and realized phenotypic merit is not linear, substantial realized paternal heterosis may be observed due to optimization of gene frequencies through use of the crossbred male. This result is likely for categorical traits or traits with an intermediate optimum breeding value. At the production system level, the appropriate unit of evaluation is the cohort composed of a male and the set of females that are exposed to the male for breeding. At this level, potential advantages of the crossbred male may accrue due to both heterosis for male fertility and optimization of gene frequency.

Expression of nuclear-cytoplasmic interactions and heterosis in quantitative traits of oats (Avena spp.)

Abstract: Nuclear and cytoplasmic genes from 10 diverse Avena sterilis L. accessions were introgressed into four Corn Belt oat (A. sativa L.) cultivars. Grain and straw yield, harvest index, heading date, height, unit straw weight, and vegetative growth index were evaluated in the BC2 generation of 76 cytoplasmic isopopulations. Means of all seven traits in the BC2 of ‘Tippecanoe’ matings were greater than Tippecanoe due to introgression of A. sterilis germplasm, whereas means of all seven traits in BC2 populations of ‘Ogle’ were inferior to those of Ogle. BC2 populations of matings involving ‘CI 9170’ and ‘CI 9268’ were variable, with some trait means being greater than those of the recurrent parents and some being lower.

Environment-dependent heterosis in Drosophila melanogaster.

Abstract: drawn about the effect of environment for these traits. Every pair of lines displayed heterosis for fecundity both under optimal and crowded development conditions, while only 2 pairs of lines showed significant heterosis for fecundity at low temperature. Contrary to what is usually found for most traits, heterosis for fecundity was greater in the optimal environment. Hybrids were more affected by environmental stress than their inbred parents, but the error variance within environment was lower for the hybrids. This suggests that the greater homeostasis of hybrids to minor changes in environment can not be extended to major changes in the environment in which different sets of genes may be implicated.

Maternal heterosis and grandmaternal effects in beef cattle: postweaning growth and carcass traits.

Abstract: Crossbred steer and heifer progeny from 5-, 6- and 7-yr-old dams produced in a four-breed diallel crossing experiment involving the Brown Swiss, Red Poll, Hereford and Angus maternal grandsires and maternal granddams were evaluated for postweaning growth and carcass traits to estimate breed mean maternal heterosis, maternal heterosis for specific breed cross females, average maternal heterosis for all crosses, breed grandmaternal effects and net breed effects in crosses. All progeny evaluated were born in 1979 and 1980 and were sired by 7/8 or 15/16 Simmental bulls. Average maternal heterosis was significant for 200-d weight in heifers but not in steers and was not significant for final weight (444-d) in either heifers or steers. The effects of maternal heterosis on postweaning growth were not important. Differences among breeds in mean maternal heterosis values were small for growth-related traits. Breeds did not differ (P greater than .05) in grandmaternal effects for growth-related traits; Brown Swiss tended to be highest, Red Poll lowest, with Hereford and Angus intermediate. Differences in net breed effects in crosses favored Brown Swiss over the three other breeds and were generally significant for growth traits. Average maternal heterosis, though generally positive, was not significant for carcass traits on either an age-constant or weight-constant basis. Differences among breeds were small in grandmaternal effects, specific heterosis and net effects in crosses for carcass traits associated with both weight or composition; generally the Brown Swiss breed was favored on carcass traits associated with weight in the age-constant analysis and generally had a higher lean-to-fat ratio than the three other breeds in both the age-constant and weight-constant analyses.

Combining ability and heterosis for quantitative powdery mildew resistance in barley

Abstract: The estimation of combining abilities and heterosis for quantitative resistance against Erysiphe graminis f. sp. hordei of eight spring barley (Hordeum vulgare) cultivars is presented. Fur this purpose a half diallel cross and its parents were arranged in five Latin rectangles, each inoculated with a current mildew isolate. Significant general combining ability was found whereas specific combining ability was non-significant. A great pan of the general combining ability could be explained by variety effects. Significant variety heterosis was obtained too. Significant average heterosis was obtained but us effect was small. Among those selected for this study, ‘Grit’ and ‘Hora’ were the best parents for further crosses.

Periodic rotational crosses. I. Breed and heterosis utilization.

Abstract: Periodic rotational crosses differ from conventional rotations by using sire breeds an unequal number of generations but in a regular sequence. Formulas for breed composition and heterosis in offspring from periodic rotations at equilibrium averaged over all generations of a cycle and for each generation of the cycle are presented. Coefficients of squares and products of breed differences and heterosis used to calculate inter-generational variance are also derived. Several specific periodic rotations utilizing a range of breed proportions were found to use from 70 to 95% as much heterosis as conventional rotations using the same number of breeds equally. Estimates of swine and cattle additive breed and heterosis effects taken from the literature were applied to the formulas. In both the swine and cattle examples, periodic rotations were found that equaled or exceeded the conventional rotations using the same number of breeds and also had lower inter-generational variance.

Crossbreeding and Meat Quality in Pigs

Abstract: A review is presented on heterosis for meat quality. The classical view, i.e. no significant heterosis, is to be revised to some extent when considering specific meat quality traits in specific crosses. Evidence is presented for two main deviations from additive inheritance of breed differences in crossing. Abnormally fast rate of fall in pH in the early post-mortem period, an indicator of typical PSE meat condition, appears to be inherited as a recessive or partially recessive trait in Pietrain crosses. The halothane locus is likely to play the major role in this respect. On the other hand, it may be hypothesized that the comparatively larger extent of fall in pH (i.e. lower ultimate pH) shown by Hampshire purebreds is inherited as a dominant or partially dominant trait in Hampshire crosses. Recent results suggest that a dominant major gene could be involved in this “Hampshire effect” on meat quality.

Studies on Hybrid Vigour in Egg Plant (Solanum Melongena Linn.)

Abstract: The manifestation of hybrid vigour in 30 Fj hybrids was studied for five characters viz. yield per plant (marketable), fruit weight, fruit length and fruit girth. Crosses BR-112 × Aushey, PBR-61 × K 202-14, PBR-91-1 × K 202-14 and K T 3 × K 102-14 showed significant positive heterosis over best parent K 202-9 for yield. Crosses KT3 × Vijai, PBR-91-1 × K 202-14 and PBR-91-1 × Aushey for number of fruits, BR-112 × Arka sheel for fruit weight, PBR-61 × Azad Kranti for fruit length showed significant and positive heterosis over better parent. None of the crosses displayed significant and positive heterosis for number of fruits, fruit weight and fruit girth over best parent.

Genetic Changes Over Six Generations in a Pedigree Breeding Programme in Sorghum

Abstract: Six consecutive generations (F1 to F6) of a cross between CSV 8R and SPV 104 were studied during rabi (postrainy) season at Hyderabad. The F3-f6 progenies have undergone assortive mating. They were also subjected to selection for grain yield and seed size. The grain yield was highest in F1 followed by successive depression in F2 and f3 generations. After marginal increase in F4, the yield levels were almost consistent in subsequent generations. There was decrease in plant height and increase in days to flower and seed size in later generations. Heterosis over superior parent was highest (27.3%) for grain yield. It was mainly governed by dominance gene effect (h). The highest inbreeding depression for grain yield was observed in F3 due to segregation of heterozygous plants which had selective advantage over the relatively homozygous plants in F2 and high magnitude of dominance which governs the yield heterosis. The change in mean phenotypic value of other characters has been due to correlated response.

Hormones and Heterosis in Plants

Abstract: Heterosis, or hybrid vigor, occurs when hybrid performance exceeds that of either parent. Heterosis occurs in animals and is particularly common in plants. It is probably important in evolution since heterozygote superiority may ensure the maintenance of genetic polymorphism in natural populations. Further, heterosis is extremely important to agriculture and horticulture and is of increasing importance in forestry. The dramatic yield improvements in cereal crops in the twentieth century have been, in large part, due to the utilization of heterosis. Inbreeding depression refers to the reduction in phenotypic vigor following self-fertilization and is the complementary process to heterosis.