Additive Epistatic Effects Research Articles

Generation Mean Analysis of Inheritance of Resistance to Pyrenophora teres in Barley

AbstractF1, F2, Fl × parentl (BC1), and Fl × parent2 (BC2) generations resulting from four crosses among seven cultivars of barley used in national and international breeding programmes were tested at the seedling stage for their resistance to a mixture of five isolates of Pyrenophora teres. Four methods were used to assess disease resistance: infection type (IT), average lesion size (ALS), number of lesions per unit leaf area (NL) and percent leaf area infected (PLAI). Gene actions were estimated by generation mean analysis on each of the four crosses and on each of the evaluation methods. Significant additive and additive × additive epistatic effects were found. Infection type and percent leaf area infected were found to be highly correlated in all four crosses. These results suggest that barley breeders could improve the level of resistance to P. teres by making appropriate crosses between highly susceptible barley cultivars.

Quantitative genetics of doubled haploid populations and application to the theory of line development.

The line value of a genotype is defined as the expected value of all lines that can be derived from this genotype. Specific genetic effects are defined for this value: only additive and additive by additive epistatic effects are necessary. There is no dominance effect for such a value. A general expression for the covariances between related lines is given. From a design with several lines per haplodiploidized plant taken at random from a population it is possible to estimate the additive variance for line value and the variance of additive by additive epistasis for line value. Variances of higher order epistasis can be estimated with a two-factor mating design in which a cross is replaced by the population of lines that can be derived from it. With a diallel or a factorial design a direct test for the presence of homozygous by homozygous epistasis is possible. The application of the concept of line value to the theory of line development leads to simple expressions of genetic advance in one cycle of recurrent selection according to the testing system. A brief consideration of these expressions leads to the conclusion that single doubled haploid descent recurrent selection will be one of the most efficient methods for low heritabilities and with a rapid development of doubled haploid lines.

A building block model for quantitative genetics.

We introduce a quantitative genetic model for multiple alleles which permits the parameterization of the degree, D, of dominance of favorable or unfavorable alleles. We assume gene effects to be random from some distribution and independent of the D's. We then fit the usual least-squares population genetic model of additive and dominance effects in an infinite equilibrium population to determine the five genetic components--additive variance sigma 2 a, dominance variance sigma 2 d, variance of homozygous dominance effects d2, covariance of additive and homozygous dominance effects d1, and the square of the inbreeding depression h--required to treat finite populations and large populations that have been through a bottleneck or in which there is inbreeding. The effects of dominance can be summarized as functions of the average, D, and the variance, sigma 2 D. An important distinction arises between symmetrical and nonsymmetrical distributions of gene effects. With symmetrical distributions d1 = -d2/2 which is always negative, and the contribution of dominance to sigma 2 a is equal to d2/2. With nonsymmetrical distributions there is an additional contribution H to sigma 2 a and -H/2 to d1, the sign of H being determined by D and the skew of the distribution. Some numerical evaluations are presented for the normal and exponential distributions of gene effects, illustrating the effects of the number of alleles and of the variation in allelic frequencies. Random additive by additive (a*a) epistatic effects contribute to sigma 2 a and to the a*a variance, sigma 2/aa, the relative contributions depending on the number of alleles and the variation in allelic frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Inheritance of Potassium Efficiency, Sodium Substitution Capacity, and Sodium Accumulation in Tomatoes Grown Under Low-potassium Stress

Abstract One hundred tomato (Lycopersicon esculentum Mill.) strains were grown under low-K stress (0.071 mm K) in the absence and presence of added Na to identify strain differences in efficient K use, efficient substitution of Na for K, and upper leaf Na accumulation. Five strains, selected as representing extreme differences for K efficiency and Na substitution capacity, were used as parents to create a series of F1, F2, and backcross generations to study the inheritance of K efficiency, Na substitution, and upper leaf Na accumulation of tomatoes grown under low-K stress. Reciprocal differences in the F1 generation were relatively unimportant in the inheritance of K efficiency, Na substitution capacity, and Na accumulation. K efficiency in the absence of Na was a trait of low heritability, with highly significant additive, dominance, and additive × additive epistatic effects. Na substitution capacity was highly heritable, with highly significant additive and dominance effects. Na accumulation also was highly heritable, with highly significant additive effects. Moderately high correlations were observed between Na accumulation and Na substitution capacity within genetically segregating generations.

Inheritance of quality traits in processing tomato (Lycopersicon esculentum Mill.)

The genetic basis of pH, colour and soluble solids in processing tomato is examined. In a first experiment, aimed at identifying the base populations with which to start selection, parents, F1 and F2 progenies of an 8 × 8 diallel cross without reciprocals were tested. The results indicate that additive, dominance and additive x additive epistatic effects were noticeable for the three characters. Higher order interlocus interactions were also detected. As to the soluble solids, a trait for which higher order epistatic effects were less marked, the breeding potential of the cross combinations was assessed by calculating the expected mean values at the F∞ generation. Some cross populations having ‘C33’ or ‘C35’ as parent appeared to be superior. A second experiment was conducted to collect data on the heritability of the foregoing qualitative traits by utilizing the regressions of F3 offspring on F2 parents. The low heritability coefficients observed would suggest the ineffectiveness of individual selection in early generations. In both the F2 and F3 generations rather low correlation coefficients among the three quality traits were observed.

Inheritance of Glandular Trichomes in Tobacco

Trichome type and density may be responsible for genotypic differences for insect resistance and leaf chemical constituents in tobacco (Nicotiana tabacum L.). We investigated the inheritance of glandular trichomes to determine the feasibility of selecting this trait in a breeding program. Segregating generations were derived from crosses among several tobacco introductions (T.I.) and ‘Ky 14’, a burley tobacco cultivar, which differ in densities of glandular trichomes. Microscopic examinations of the abaxial surface of 20 cm long leaves were made in the field in 1982 and 1984. The F1, F2, and F3 generation means for glandular trichome density were much lower than midparent values. Additive genetic effects for trichome density were highly significant, as were the estimates of the additive ✕ additive epistatic effects. Dominance effects were significant only in the cross T.I. 1112 ✕ T.I. 1068. Heritability estimates, obtained by regression of F3 family means on F2 parental values, were 0.74, 0.77, and 0.95 for the populations derived from crosses between T.I. 1112 and T.I. 1068, T.I. 1406, and Ky 14, respectively. Chi‐square analyses of F2 data for the presence or absence of glandular trichomes indicated Ky 14 and T.I. 1406 had alleles at two loci that were different from those present in T.I. 1112, and T.I. 1068 differed from T.I. 1112 at three loci. Genes at these loci may affect glandular trichome density as well as presence or absence of glandular trichomes, but other genetic factors, including those influencing leaf size and shape, may affect trichome density.

Quantitative genetic variation in an ecological setting

The machinery was developed to investigate the behavior of quantitative genetic variation in an ecological model of a finite number of islands of finite size, with migration rate m and extinction rate e, for a quantitative genetic model general for numbers of alleles and loci and additive, dominance, and additive by additive epistatic effects. It was necessary to reckon with seven quadratic genetic components, whose coefficients in the genotypic variance components within demes, σ Gw 2, between demes within populations, σ s 2, and between replicate populations, σ r 2, are given by descent measures. The descent measures at any time are calculated with the use of transition equations which are determined by the parameters of the ecological model. Numerical results were obtained for the coefficients of the quadratic genetic components in each of the three genotypic variance components in the early phase of differentiation. The general effect of extinction is to speed up the time course leading to fixation, to increase σ r 2, and to decrease σ s ̄ 2 (with a few exceptions) in comparison with no extinction. The general effect of migration is to slow down the time course leading to fixation, to increase σ Gw 2, at least in the later generations, and to decrease σ s ̄ 2 (with a few exceptions) in comparison with no migration. Except for these, the effects of migration and extinction on the variance components are complex, depending on the genetic model, and sometimes involve interaction of migration and extinction. Sufficient details are given for an investigator to evaluate numerically the results for variations in the quantitative genetic and ecological models.

Characterization of genes involved with classical conditioning that produce differences between bidirectionally selected strains of the blow fly Phormia regina.

Mean response levels for classically conditioned proboscis extensions in hybrid generations from a cross between bidirectionally selected strains of blow flies were used in a biometrical analysis. The best-fitting genetic model suggests the presence of additive, dominance, and digenic epistatic effects from at least four autosomal and X-linked genes. Neither maternal nor Y-linked effects were detected. Earlier studies have described the genetic and behavioral relations between the central excitatory state (CES) and classical conditioning. That evidence indicated that covariability of the two traits is produced by one autosomal gene. The results herein are consistent with such a hypothesis, and they explain why the CES—conditioning correlation is not perfect. Finally, knowledge that some genes associated with conditioning are located on the X chromosome and, therefore, are independent of the CES gene will facilitate efforts to identify new single genes affecting associative learning inPhormia.

Inheritance of seed protein and seed oil content in early maturing soybean

The inheritance of seed protein, seed oil, and the sum of protein and oil was investigated in two early maturing soybean crosses, 'Maple Presto' × 'Sioux' and 'Maple Presto' × X446-2-1, in 2 years (1981 and 1982) at one location (Winnipeg). Analyses of variance of the parental performance over years indicated that the parents differed significantly for all three traits studied and that genotype by year interactions were effectively zero. Generation means analysis indicated that gene action for seed protein was primarily additive, with partial dominance for low protein. Seed oil was also conditioned primarily by additive gene action. Partial dominance was not consistently detected over years and therefore was of minor importance. Additive × additive epistatic effects for seed oil were also detected but were not consistent over years. The sum of seed protein and oil was conditioned solely by additive gene action. Variance analyses indicated a predominance of additive genetic variance for all three traits. Dominance variance was also detected for both seed protein and the sum of protein and oil. Broad sense heritability for the F2 generation ranged from 76 to 83% for seed protein and from 68 to 86% for the sum of protein and oil, while narrow sense heritability ranged from 34 to 72% for seed protein and from 39 to 65% for the sum of protein and oil. Narrow sense heritability values equalled broad sense values for seed oil and ranged from 58 to 68%. Heritability was also estimated from standard unit parent – progeny regression analyses and values for all three traits were found to approach the variance analyses estimated broad sense heritabilities. Comparisons with the results of late maturing soybean crosses are made and implications of the results obtained in this study on early maturing soybean breeding programs are discussed.Key words: Glycine max, heritability, 00 and 000 maturity groups, breeding strategies.

Estimation of maternal, sex-linked and additive x additive epistatic gene effects for body size of Tribolium

The genetic structure of two quantitative traits, 13-day larval weight and pupal weight, in two unselected populations of Tribolium castaneum was investigated by the genetic model of Carbonell et al. (1983). The variability among two and three-way crosses was analyzed into components due to: general and specific combining abilities, maternal, sex-linkage, specific reciprocal and additive-by-additive epistasis. Also, indirect evidence of higher order epistasis was studied. It is concluded that the heterotic trait larval weight is highly affected by sex-linked genes and by non-additive gene action with additive-by-additive as well as higher order epistasis playing major roles. Pupal weight, on the other hand, is determined mostly by additive gene action although epistasis is also a significant source for genetic variability. Both traits are significantly influenced by maternal effects.

Inheritance of seed size in cowpea (Vigna unguiculata (L.) Walp.)

The inheritance of seed weight in cowpea was examined in a field planting of the parents, reciprocal F1s, F2s and backcrosses to both parents of a cross between TVu 1977-OD (small seeded) and ACC 70002 (large). Seed weight was inherited quantitatively and small seed was partially domiminant to large seed size. Gene action was predominantly additive but dominance and additive × additive epistatic effects were also significant. Broad and narrow sense heritabilities were 85.1±5.3% and 75.4±18.6% respectively. The minimum number of loci involved in the inheritance of seed size was eight, and each gene pair contributed up to 1.02 g increase to seed weight. The estimate of genetic advance from F2 to F3 generations with 5% selection intensity was 3.58 g.

Inheritance of Seedling Root Length and Relative Root Weight in Cotton1

A perennial problem in cotton, Gossypium hirsutum L., involves obtaining a vigorous, uniform stand when planted early. Strains that grow roots longer and higher in relative root weight (mg/mm length) than currently used cultivars when temperatures are cool may help alleviate this. Using the standard cotton, cool temperature (18°C) germination test we determined root lengths and relative root weights for 124 day‐neutral composite F3 strains. Variability among lines was significant for each seed and seedling parameter. Fixed model diallel analyses of five strains indicated that among the five strains one would have difficulty in selecting for long roots with high relative root weight. Generation mean analysis indicated from one of two crosses that large amounts of additive, dominance, and additive by additive epistatic effects were present for the two primary root traits. One should thus be more successful if selection is delayed to the F3 to allow genetic recombination of additive and additive by additive epistatic genes to occur. Recurrent selection should be a useful method of breeding. The cross of strains 3822 ✕ 3851, involving accessions T‐214 and T‐225, respectively, should be useful for developing lines with root length equal or longer than ST 213 and relative root weight greater than ST 213. We speculate that plants with long roots and a high relative root weight should possess increased levels of resistance to seedling disease through a mechanical type of resistance; i.e., the plants should have more root tissue to slough off as diseased tissue and yet maintain a viable root system and a healthy plant than would plants with short roots with a low relative root weight.

Gene Effects for Resistance to Kernel Shattering in a Barley Cross1

Yield losses from shattering have necessitated the development of shatter resistant cultivars, and breeding procedures depend on the type of gene action conditioning the trait under study. Shatter resistance was measured in barley (Hordeum vulgare L.) as the force required to free a spikelet from the rachis. Measurements were made on single random plants of four generations representing six populations (parents, F1, F2, and single backcrosses) from a cross between two parental lines. All populations were grown near Bozeman, Mont. in both 1968 and 1969. In both years, dominance for shattering susceptibility as well as additive gene effects separating the parents were detected. In 1969, a significant additive ✕ additive epistatic effect was detected, and the dominance effect was more than twice as large as it was in 1968. These results suggest that the inheritance of shattering resistance is complex and the expression of gene effects appears to be sensitive to environmental (year) conditions. However, because shatter resistance is recessive and because only the additive ✕ additive epistatic component was significant, in this cross direct selection for shattering resistance in early generations should be effective. More crosses must be evaluated before a general breeding scheme can be proposed.

INHERITANCE OF PER CENT TOTAL ALKALOIDS INNICOTIANA TABACUML. II. GENETIC EFFECTS OF TWO LOCI IN BURLEY 21 × LA BURLEY 21 POPULATIONS

The genetic effects and the relative contribution of two loci to the level of total alkaloids in burley tobacco (Nicotiana tabacum L.) were determined. The nine genotypes for a two-locus system were developed and evaluated in two environments. Significant additive effects were found at both loci, a dominance effect was significant at one locus, and the additive × additive epistatic effect was significant. All interactions between genetic effects and environments were nonsignificant. The relative dosage effects of the loci were approximately 2.4 to 1.

Inheritance of Lint Quality Characteristics in Interspecific Crosses of Cotton1

In interspecific crosses between varieties of upland (Gossypium hirsutum L.) and Egyptian (G. barbadense L.) cotton, tested in Israel from 1959 through 1965, F1 performance for upper‐half‐mean and mean lint length exceeded that of either parent by 10 to 16% and 6 to 13%, respectively. The uniformity ratio of F1 plants was slightly lower than the parental mean. F2 performance for lint length was slightly above parental mean, but a significant F2 deviation was detected for this trait. There were indications that additive, dominance, and additive ✕ additive epistatic effects were operating in the inheritance of lint length.The tensile strength (1/8‐in. gauge, i.e. T1 of the F1's lint was almost as high as that of the stronger G. barbadense parental varieties. The magnitude of heterosis was 9 to 15% for this trait, with no F2 or backcross deviations. This indicated that only additive and dominance effects were operating in the inheritance of lint strength.Micronaire measurement of lint fineness was much lower in F1 hybrids than in either parent (a negative heterosis of 12 to 19%). Only the dominance effects were detected as operating significantly in the inheritance of this trait, but there were considerable deviations from the model with no epistasis.Significant effects of general combining ability were found for lint length and tensile strength. Additive gene‐action was predominant for these traits. Dominance effects were the main cause of heterosis for all the traits of lint quality examined.

GENE EFFECTS FOR TOLERANCE TO WEATHER FLECK IN TOBACCO

Introduction Weather fleck is a physiological disorder of the plant (Figs. 1,2) which seriously damages the flue-cured tobacco crop in south-western Ontario. Airborne oxidizing agents (Burl< and Heggestad, 1956; Taylor, 1959; \Vall<er, 1961) are the main cause but the incidence and intensity of flecking has been linlied with various environmental factors such as the concentration of ozone in the air (Heggestad and Middleton, 1959; Macdowall e t al., 1963, 1964; Taylor and Rich, 1962). An excess of irrigation water (Menser and Street, 1962; Walker and Viclcery, 1961) and reduced level of nitrogen fertilizer (ildenser and Street, 1962) result in premature ripening of the leaves which favours flecking. Various chemical compounds l<nown for their antioxidant properties were suggested as preventive measures in overcoming weather fleck damage in tobacco fields (Siegel, 1962; Silbur, 1964; Taylor and Rich, 1962; \Vall<er, 1961, 1966). It has also been observed that there is a considerable variability among the flue-cured varieties in the levels of tolerance to weather flecli (Burli and Heggestad, 1956; Povilaitis, 1958; Sand, 1960). When initiating the breeding program to produce flue-cured varieties exhibiting high levels of tolerance to weather flecli, which would also be suitable in other respects for western Ontario conditions, it was coilsidered essential to obtain some information on the mode of inheritance of tolerance to weather flecli in flue-cured tobacco. The present paper reports on the relationships of additive, dominant, and digenic epistatic genc effects and their relative importance in the inheritance of tolerance to weather fleck in certain varieties of tobacco.

A General Model for Genetic Effects

A model is proposed to characterize the means of a fixed set of varieties, variety crosses and other entries obtained from these varieties and variety crosses. The varieties can be pure-line varieties, inbred lines with any degree of inbreeding as well as open-pollinated or synthetic varieties as long as the varieties are in Hardy-Weinberg equilibrium. Parameters are defined for additive, dominance and additive by additive epistatic effects assuming diploid inheritance. Tests are available from the analysis of variance for deviations due to higher order epistasis (and/or linkage with additive by additive epistasis). If the model is adequate, the performance of related entries can be predicted. In certain instances, the variance of the predicted mean will be less than the variance of an observed mean.