Epistatic gene control on the yield of tomato at medium elevation in the tropical agroecosystem

Mawasid FP, Syukur M, Trikoesoemaningtyas. 2019. Epistatic gene control on the yield of tomato at medium elevation in the tropical agroecosystem. Biodiversitas 20: 1880-1886. Cultivation of tomatoes on the middle-low plain generally decreases the quantity and quality of the yield due to high-temperature stress. Increasing the size and weight of lowland tomatoes is needed to enhance national production. Information on the action and genetic model of target characters is needed in the preparation of the assembly program, especially for selection needs. This study aims to obtain genetic information and heritability of tomato yield characters, as a basis for assembling large tomato varieties for the lowlands. The study was conducted using six populations (P1, P2, F1, BCP1, BCP2, and F2) resulting from two different crosses of 99D x Tora (C-I) and 97D x Tora (C-II). The results show that the action of non-additive genes and non-allelic interactions has a large value, with duplicate epistasis being more dominant than complementary epistasis. Duplicate epistasis was found in the character of harvest time, fruit length, fruit diameter, fruit weight in cross I and flowering time, harvest time, fruit length, fruit diameter, and number of fruits in cross II, while complementary epistasis was found in flowering time, fruit weight per plant, number of fruits in cross I, and fruit weight, fruit weight per plant in cross II. Moderate to high heritability was found in the character of fruit length, fruit diameter, fruit weight, and fruit weight per plant. The values are higher in population from the cross I (99D x Tora) for each character, indicating that the cross I has a higher potential for genetic progress than cross II. Selection is recommended when the homozygosity has increased, using the Bulk method or Single Seed Decent. The two methods above can maintain variability in the next generation, so epistasis genes that control target characters are not drastically eliminated.

Genetic analysis for yield and yield attributes in greengram (Vigna radiata L. Wilczek)

Six basic generations viz., P1, P2, F1, F2, B1 and B2 of five selected crosses viz., LGG-460 × WGG-37, TM-96-2 × WGG-37, TM-96-2 × PM-112, MGG-295 × PM-110 and MGG-351 × PM-115 were studied to assess the nature and mode of gene action for yield and its component traits through generation mean analysis. In general, magnitude of dominance effects (h) has greater value than additive effects (d) for majority of the traits in all the crosses. All the traits are under the influence of duplicate epistasis besides additive type of gene effects for which bi-parental mating or inter-se mating may be adopted followed by pedigree method of selection to modify the genetic architecture of greengram for attaining higher yields with desirable properties.

Evaluation of genetic variance components for some quantitative traits in rapeseed (Brassica napus L.)

Three hybrid combinations obtained by crossing six winter rapeseed cultivars were analyzed for the impact of genes with additive and dominant effects and their interactions with inheritance of plant height and first lateral branch height. The linkage among the expected progeny means was checked using the scaling test method (Mather, 1949), while the estimates of genetic effects and mode of inheritance was made by the Generation Mean Analysis (Mather and Jinks, 1982). The additive dominant model did not prove adequate for plant height in all three crosses, and for first lateral branch height in the second and third cross. The inadequacy of the model showed epistatic gene effects were also of large importance in the inheritance of these traits. Duplicate epistasis for plant height inheritance was found in all three cross combinations and for inheritance of height of the first lateral branch in second and third cross combination. However, it should be emphasized that duplicate epistasis among dominant positive genes occurred on plant height inheritance in C1 and C3, and on inheritance of first lateral branch height in C3. Duplicate epistasis among dominant negative genes occurred in C2 on the mode of inheritance of both traits.

Assessment of components of genetic variance of mass 1000 seeds in sunflower -Heuanthus annuus L.-

Ten F1 hybrids obtained by crossing five sunflower inbred lines were used to analyze the impact of genes with additive and dominant effects and their interactions on the inheritance of mass 1000 seeds. The linkage among the expected progeny means was tested using the scaling tests method (Mather, 1949), while the estimates of gene effects and mode of inheritance were made by generation mean analysis (Mather and Jinks, 1982). The additive-dominant model was not proved adequate for all crosses in both years of study. It was adequate in crosses C1, C2, C3 and C5 in the first year and in crosses C3, C8, C9 and C10 in the second year of study. Besides the main gene effects (additive and dominant), epistatic gene effects were also of large importance in the inheritance of this trait. Duplicate epistasis between dominant decreasers was found in C1, C4, C5, C6 and C8 in the first year and in crosses C4, C9 and C10 in the second year of study. Complementary epistasis between dominant decreasers was found in cross C10 in the first year and duplicate epistasis between dominant increasers in cross C5 in the second year of study.

Polygenic mutation in Drosophila melanogaster: non-linear divergence among unselected strains.

A highly inbred strain of Drosophila melanogaster was subdivided into 20 replicate sublines that were maintained independently with 10 pairs of randomly sampled parents per generation for 180 generations. The variance between lines in abdominal and sternopleural bristle number increased little after 100 generations, in contrast to the neutral expectation of a linear increase; and the covariances of line means between different generations declined with increasing number of generations apart, in contrast to the neutral expectation of constant covariance. Thus, under a neutral model, the estimates of mutational variance were lower than for previous estimates from the first 100 generations of subline divergence. An autoregressive model was fitted to the variance of line means that indicated strong natural selection. There is no single unequivocal explanation for the results. Possible and nonexclusive alternatives include stabilizing selection on bristle number and deleterious effects on fitness of bristle mutations. The inferred strengths of selection on both traits are too high for stabilizing selection alone, and the between-line variance did not continue to increase sufficiently for pleiotropy alone to account for the observations. A third potential explanation that does not invoke selection is duplicate epistasis between mutations affecting bristle number.

Linked digenic epistasis in the inheritance of tillering and yielding ability in a cross of wheat

The nature of genetic variation in an intervarietal cross ('WG 377' × 'Sonalika') of bread wheat (Triticum aestivum L. em Thell.) was determined for grain yield and tillers per plant by analyzing 21 generation means and 36 family variances. For both traits, duplicate epistasis of linked loci in the pairs and gene dispersion was observed through the analysis of 21 generation means. The analysis of generation variances further suggested repulsion phase linkages for the gene pairs. The additive genetic component was significant for both traits in each of the analyses. Prevalence of gene dispersion suggested the possibility of high transgressive segregation. However, the task of exploiting additive genetic variation would be difficult because of duplicate epistasis and repulsion phase linkages. Considering these results a breeding procedure like biparental mating among a large number of superior F2 plants which encourages crossing-over is suggested.Key words: Triticum, linked epistasis, quantitative traits, additive effects, tillering.

ON THE INHERITANCE OF INTERSEXUALITY IN SWINE

Data of Breeuwsma (1970) were analyzed in an attempt to discriminate between major gene vs. multifactorial modes of inheritance of intersexuality in swine. Of 3708 females, 160 were intersexes with external phenotypes ranging from normal female (normal overlap) to testicular pseudohermaphrodite. Environment (litter size, parity, hormone treatment of dam) influenced detection of carriers but not origin of intersexes. Normal overlaps lowered penetrance, partly due to deaths in competition with male littermates. Phenocopies (intersex with unusual genotype or with karyotype other than 38,XX) were rare. Sex ratio variation between mating types could be ascribed to the ascertainment method. Segregation ratio estimates for female sibships increased from those with at least one to those with at least two intersexes less than expected for polygenic inheritance. The latter could not be ruled out (heritability of liability by three methods was 78%), but duplicate epistasis provided a more parsimonious explanation. Separation of litters from retrospectively known carriers into identifying and post-identifying groups produced patterns of segregation estimates supporting inheritance by few rather than many genes. Crossbred intersexes indicate homology of genes for intersexuality in several European breeds of pigs.