Showing papers on "Heterosis published in 1975"

Physiological, Biochemical, and Genetic Basis of Heterosis

Abstract: Publisher Summary This chapter describes the basic mechanism of heterosis, along with the physiological and genetic basis for this phenomenon. Heterosis is a phenomenon through which the yields of crop plants can be improved and explains the way this mechanism can be exploited more effectively and profitably. Heterosis in plants has usually been identified with hybrid vigor as a major component. Hybrid vigor is defined as the heterosis manifest, and is thus the phenotypic expression of heterosis, which is a genetic phenomenon. Heterosis can be obtained in plants, animals, and microorganisms for various economically important characters. In plants, the phenomenon is common both in cross as well as in self-pollinated crops. The crops in which heterosis has been commercially exploited or will be exploited in the near future are listed. The chapter discusses the heterosis in heterotrophs and autotrophs along with the various theories of heterosis: (1) dominance hypothesis, (2) overdominance hypothesis, (3) physiological stimulus and initial capital, (3) complementation at cellular and subcellular level, (4) balanced metabolism, and (5) hormonal and other factors.

Breed, heterosis and environmental influences on growth and puberty in ewe lambs.

Abstract: A study involving 825 spring ewe lambs was conducted to evaluate effects of breed, heterosis, type of birth and rearing, age of dam and preweaning and postweaning growth rate on occurrence of puberty before November 10. Within a breed or breed-cross, preweaning competition among twin and triplet lambs reduced lamb weights by 4 or 5 kg at 70 (weaning), 160 and 230 days of age and by about 3 kg at puberty but delayed puberty only about 1 week. Age of dam strongly influenced preweaning growth of ewe lambs, but did not significantly affect age or weight at puberty. Higher preweaning and 70to 160-day postweaning rate of growth definitely increased percentage of lambs reaching puberty by November 10 and hence reduced mean age at puberty. Percentage reaching puberty by November 10 was far higher for Finn-sired (72 -+ 4%) than for Rambouillet-sired (38 -+ 6%) crosses or purebreds (34 -+ 5%) of the Suffolk, Hampshire, Rambouillet, Dorset, Targhee, Corriedale or Coarse Wool breeds. Finn crosses reached puberty earlier (219 days) and at lighter weight (40 kg) than Rambouillet crosses (238 days and 44 kg) or purebreds (245 days and 45 kg). Domestic breed of dam means ranged from 27 to 57% in estrus before November 10, from 225 to 240 days in expected age at puberty and from 39 to 50 kg in expected weight at puberty. (

Laboratory Hybridization and Mating Period Studies Using Two Pheromone Strains of Ostrinia nubilalis

Abstract: Strong laboratory reproductive isolation exists between 2 strains of Ostrinia nubilalis (Hubner). This reproductive isolation is related to the use of different sex pheromones by the 2 strains, and differences in mating periodicity. Hybrid progeny, when produced, exhibit heterosis, but no great genetic deficiencies are observed when the hybrids are inbred. Thus the 2 strains appear to possess the same basic genetic systems, with enough variation introduced through hybridization to cause hybrid heterosis.

Heterosis and Combining Ability in Exotic Soybean Germplasm1

Abstract: The objectives of this study were to determine the magnitude of heterosis for yield, its components, and other agronomic characters and to determine the relative importance of general combining ability (GCA) and specific combining ability (SCA) in spaced plants soybean [ (L.) Merr.] hybrids with both adapted cultivars and exotic strains as parents.The experiment, conducted at West Lafayette, Ind. in 1971 and 1972, used a partial diallel mating design with 12 parents. There were three parents from each of the following origins; locally adapted cultivars or strains, Manchurian, Chinese, and Korean. Thirty different F combinations were produced and, along with their parents, planted in a randomized, complete block design.Heterosis for yield was greater than that for any other character with a high-parent value of 8.0% averaged over both years. Twelve of the 30 hybrids outyielded the midparent. Number of pods/plant was the most heterotic of the yield components. Number of seeds/pod and seed size of the F's was with few exceptions, intermediate to parental values, as were maturity, height, lodging, and harvest index. Heterosis for plant weight was similar to that for yield, both in magnitude and in the hybrids expressing it.Significant GCA effects were found for all characters. SCA effects were significant for seed size, maturity, and height. The years × GCA interaction was significant for yield, number of pods/plant, maturity, lodging score, plant weight, and harvest index. Years × SCA were significant for ntunber of seeds/pod, maturity, lodging, and harvest index.

Codominant isoenzymic alleles as markers of genetic diversity correlated with heterosis in maize (Zea mays).

Abstract: The average F1 yields were found to be significantly correlated with the genetic diversity of the parental strains calculated from the zymogram patterns of five enzyme systems in a sample of eight strains and their diallelic crosses. Despite the relatively small number of loci (eight) studied, there is evidence that these codominant alleles are good markers for genetic heterogeneity that is a source of heterosis.

Heterosis, combining ability and reciprocal effects for agronomic and chemical characters in sesame

Abstract: The extent of heterosis was examined for six agronomic and two chemical characters in a complete diallel cross experiment involving a set of ten self-pollinated varieties of sesame (Sesamum indicum L.) of diverse ecogeographic origin. The magnitude of general and specific combining ability variances and differences in reciprocal F 1 hybrids were also investigated. Heterosis was, on average, highest for seed yield (33%), followed by number of capsules per plant (16%). Mean percent heterosis was small for earliness, plant height and number of primary branches, while it was insignificant for number of secondary branches and percentage of oil. Significant negative heterosis was observed for percentage of protein. Percent heterosis was generally higher in Indian x exotic crosses than in Indian x Indian and exotic x exotic crosses. The exotic lines appeared to be useful in Indian sesame breeding programmes, particularly in the improvement of earliness, number of secondary branches, seed yield and protein content. Additive as well as non-additive gene action seemed to govern the expression of the various characters studied. General combining ability variances were predominant for days to flowering, plant height, number of primary branches and number of secondary branches, while specific combining ability variances were in moderate to high proportions for seed yield, percentage of oil and percentage of protein. T.M.V.-2 and S. I. 770 were the best general combiners for many of the characters while S. I. 1783 and Sel-R were found to be the best for earliness and oil content respectively. Significant variances due to reciprocal effects were also detected for some of the characters. Isolation of pure lines was preferred to production of hybrids in sesame, and crossing selected sibs in the early segregating generations followed by inbreeding seemed to be a desirable breeding procedure.

Genetic Analysis and Plant Improvement

Abstract: CONTENTS INTRODUCTION . . ...... 279 MUTANT SELECTIVE SCHEMES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 AN APPROACH TO ELUCIDATE THE METABOLIC LESION UNDERLYING MORPHOLOGICAL MUTATIONS 283 QUANTITATIVE INHERITANCE AND HETEROSIS 287 DEVELOPMENTAL GENETICS AND CROP yIELD 295

Inheritance of pericarp thickness in short season maize inbreds

Abstract: Pericarp thickness of 16 short-season inbred lines of corn (Zea mays L.) ranged from 35 to 126 μm with an overall mean of 82 ± 5 μm. The mode of inheritance of this trait was studied in two experiments. Two inbreds representing the extremes of pericarp thickness, their F1 and F2 generations, and both first generation backcrosses were included in Experiment 1. The inheritance of pericarp thickness proved to be quantitative in nature. All gene effects were significant, but epistatic effects, particularly dominance × dominance, were the largest in this particular cross. This could have resulted from bias due to linkage disequilibrium. Experiment 2 was a diallel set of 5 inbreds to include the parents and all possible single crosses, but not reciprocals. Diallel graphic analysis of these data indicated partial dominance for thin pericarp with minimal epistasis. Analysis II of Gardner and Eberhart showed that the mean square for line effects was several times larger than the heterosis estimates, indicating a h...

Diallel analysis of growth traits in mice.

Abstract: Two replications of a complete diallel cross experiment were performed among four partially inbred lines of mice. These inbred lines originated from a random-bred ICR strain and were produced by 12 generations of full sibbing ( F ≃ 92%). Individual body weight was recorded for each animal at 12, 21, 42 and 56 days of age. Body weight gain traits were examined for intervals 12-21, 21-42 and 42-56 days. Simultaneous least squares analyses of inbred and linecrossed groups were used. Sex differences were highly significant for all traits. Replicate differences were significant but made a small contribution to the total variation. Inbred lines differed greatly. Crosses showed growth trends similar to their contemporary maternal and paternal inbreds. Heterosis was highly significant for all traits except 21-day weight. Inbreds were heavier at 12 days of age, but linecrossed progeny were superior to inbreds for all post-weaning weights. General combining ability was highly significant for 12- and 56-day weights and 21-42-day gain. Specific combining ability was highly significant for 21-day weight, 12-21- and 42-56-day gain. Significant maternal effects were found for all individual weights but not for 12-21- and 21-42-day gain. Residual reciprocal effects were significant for all traits. Estimated variances among linecrossed groups contained a large maternal component, a fluctuating additive genetic component and consistent non-additive genetic influence on all growth parameters measured.

Weight gain and heterosis at different stages of development of the rat.

Abstract: Diallel crosses among four highly inbred lines of rats were made in order to evaluate their combining ability at 10 day intervals during postnatal growth. Analyses were undertaken to consider the relative magnitudes of different components of variation, including a heterotic effect, over a long developmental period. A general analysis of variance for least square means of body weights indicated that postnatal growth was influenced greatly by the maternal lines and to a lesser extent by the paternal line. Heterosis was measured as a statistically significant difference in body weight gain at 10 day intervals between the hybrid and either the averaged mean of the parent lines or the mean of the largest parent line. Of the effects analyzed, heterosis accounted for a major part of body weight variability in both sexes between 30 and 100 days of age but reached much higher levels in male than in female progeny. The heterotic response was most pronounced during the rapid growth phase; that is, between the ages of 20 to 50 days. Although interesting specific exceptions were observed, heterotic responses generally became more pronounced with increasing age through 100 days. Evidence for differential heterosis associated with particular lines was present in male progeny at growth stages immediately preceding and following the phase of most rapid growth. Specific combining ability, however, was generally lacking. Analyses of specific matings indicated that heterosis, in the lines tested, is a variable phenomenon which may be dependent upon the degree of genetic divergence between inbred parent lines and the combining ability of the genotype involved.

Heterosis, sex and maternal interactions in crosses among inbred lines of mice.

Abstract: All possible crosses and reciprocals were made among four inbred lines (F = 92%) developed from 12 generations of full-sib mating. All lines originated from a common outbred base population of ICR-albino mice. Data were obtained from 356 litter containing 2,734 mice to evaluate heterosis, reciprocal effects, sex effects and their interactions as they affect body weight and weight gain. Heterosis was significant for most of the postweaning traits (42- and 56-day weight and gain from 21 to 42 days). Nonadditive gene action may have included overdominance and epistasis since both reciprocal linecrosses were generally heavier than those of the better inbred lines. Although significant differences in reciprocals and inbred lines were not frequent, there were sufficient differences to indicate that lines varied in the fixation of loci during inbreeding. Sex-heterosis interactions were significant for 12 of 30 possible cases. However, eight of the 12 significant interactions occurred in crosses involving only one of the lines. The interactions were of the divergent type and arose from males exhibiting more heterosis than females. Overdominance in genes on the sex chromosomes modified by other loci (epistasis) was proposed as a possible explanation for these results. Some sex-linkage affecting growth was evident from the interaction of sex with reciprocal effects.

Genetical Studies in Bhindi (Abelmoschus Esculentus L.) Moench)—Gene Effects and Heterosis*

Abstract: Six genetic populations (two parents, one each F1 and F2 and two back-crosses; of a cross were raised during 1970 at U. P. Institute of Agricultural Sciences, Kanpur. Gene effects, heterosis and inbreeding depression were estimated. Positive heterosis was recorded for plant height, days to flower, internode length, fruit thickness, number of fruits per plant and yield per plant. Inbreeding depression was observed in four characters. On the other hand, respect of number of nodes and fruit length F2 was found superior to F1. Dominance gene effects (h) and additive x additive (i) and additive x dominance (j) types of epistasis were found important in the expression of the characters. Duplicate type of epistasis was found more prominent than complementary one. It was suggested that search for varieties or cultures exhibiting better general combining ability should be made for entering them into the hybridisation programme.

Heterosis in Balsam

Abstract: A diallel experiment of 5 parents of balsam (Impatiens balsamina L.) double was conducted to select most promising lines having more number of double flowers of large size. The characters included for investigation were plant height, number of branches per plant, number of flowers per plant, number of petals per flower and size of the ffower. Heterosis was observed for all characters and the performance of F1 hybrids was better than the top parent. The m.s.s. for g.c.a. was higher than that of s.c.a. Gene action was found additive in nature without any epistasis for all characters except flowers per plant where epistasis was of complementary nature. The association of excess of recessive genes with high values was observed for all characters.

Heterosis and Genetic Architecture for Oil Content in Mustard

Abstract: Heterosis and genetic architecture of oil content in mustard (Brassica juncea Coss) was studied in a complete diallel set of eight parents including reciprocals. Combining ability analysis indicated significance of GCA, SCA and RCE variances. Equal magnitude of GCA and SCA indicated the role of both additive and non-additive type of gene action. Contribution of RCE to the total variances was also appreciable. Highest mean value, highest heterosis over the better parent and high SCA effects were observed in cross combination of RC-5 × T-16. T-16 was found to be the best general combiner followed by F-58.

Heterosis and components of genetic variation for protein and lysine content in some grain sorghums.

Abstract: Twelve varieties representing six geographical regions and nine taxonomic groups from a World Collection ofSorghum were used in a diallel and line X tester analysis of the nature of genetic variation for protein and lysine content. In a majority of crosses, heterosis was negative for protein, and positive for lysine.

Heterosis and Combining Ability in Opium Poppy

Abstract: The degree of heterosis and nature of combining ability in opium poppy were studied in a set of diallel crosses of five varieties selected from the various parts of the country. Heterosis was significantly marked for capsule number and opium yield. But a poor percentage of heterosis was shown by the different hybrids in case of morphine percentage. Both g.c.a. and s.c.a. variances were significant for all the characters indicating the importance of both additive and non-additive gene action. It was evident from g.c.a. effects of parents and s.c.a. effects of crosses that both capsule number and opium yield can be improved through heterosis breeding. The predominance of additive component for capsule weight indicated that this character can be improved through the isolation of desirable recombinants. At present it is difficult to suggest as to how a true breeding high morphine line can be produced.

Absence of a correlation between mitochondrial complementation and root weight heterosis in sugarbeets

Abstract: Oxidative phosphorylation of sugarbeet root mitochondria isolated from 11 hybrids and their parental inbreds, and of mixtures of mitochondria from the parental inbreds, were measured at four different sampling stages, (Aug. 1–7, Sept. 1–7, roots stored at 5°C, and regrowth of stored roots). Mitochondrial complementation (the increased efficiency or ADP:0 ratio of mixtures of inbred mitochondria) was calculated for each hybrid at each stage. When beets were growing rapidly (Aug. 1–7) it was small but at the other stages it was absent. Only at the Aug. 1–7 sampling stage was there a significant correlation (0.75) between mitochondrial complementation and root weight heterosis. The small complementation effects made it difficult to detect differences in complementation, and thus difficult to predict root yield heterosis. Thus, this technique is not recommended as a tool in sugarbeet breeding.