Estimation of Gene Action for Seed Yield and Component Traits using Generation Mean Analysis in Pigeonpea [Cajanus cajan (L.) Millspaugh]

Background: For improvement of quantitative traits the information on nature of gene action is an important asset for plant breeders. However, the information on gene action for yield and its attributes is scanty in pigeonpea crop. Methods: The present experiment was carried out during kharif 2018-2020 at GBPUAT, Pantnagar, Uttarakhand. The experimental material consisted of six generations of three crosses viz., PADT-16 × PUSA 992, PADT-16 × UPAS 120 and PADT-16 × PAU 881. The observations were recorded on nine morphological characters. The gene action was estimated by three parameters model of Jinks and Jones if scaling tests were non significant and six parameters model of Hayman if scaling tests were significant. Result: For majority of traits in all three crosses, epistatic gene action was present as scaling tests were found to be significant. However, for traits number of primary branches, number of secondary branches and number of seeds per pod in cross PADT-16 × UPAS 120 a simple additive/dominance model was found to be adequate. In general, magnitude of dominance was found to be higher as compared to corresponding additive gene action. The high magnitude of dominance indicated that heterosis breeding is rewarding in these characters.

Estimation of Gene Action and Interaction for Some Quantitative Characters in Rice (Oryza sativa L.) by Generation Mean Analysis

The present investigation was conducted to understand the genetic action for controlling the inheritance of some quantitative characters. The experimental materials consisted of three rice varieties, i.e., Mahsuri, Bhutmuri, IR36 and F1, F2, and F3 populations of Mahsuri×Bhutmuri (Cross I) and IR36×Bhutmuri (Cross II). To conduct the generation mean analysis, the parents and their F1, F2, and F3 populations were evaluated during June to October month of Kharif 2016 and Kharif 2017. Generation mean analysis was done for eighteen quantitative characters following the five parameter model. The Analysis of Variance revealed significant differences among the five generations for all the characters studied. The results of the scaling tests and joint scaling test revealed that the Simple additive-dominance model was inadequate for days to 50% flowering, days to maturity, number of panicles plant-1, number of primary branches panicle-1, number of secondary branches panicle-1 in Cross I, while it was for plant height, number of tillers plant-1, number of panicles plant-1, number of grains panicle-1, number of filled grains panicle–1 and fertility % in Cross II. Hence, the present studies have revealed that epistasis as a basic mechanism that cannot be ignored. Thus, formulating breeding policies on only main gene effects i.e. additive and dominance could be misleading.

The impact of linkage disequilibrium and epistasis in the studies of inheritance based on Hayman’s diallel and generation mean analysis

This simulation-based study assessed the impact of linkage disequilibrium (LD) and epistasis on Hayman’s diallel and generation mean analysis, assuming hundreds of genes, variable degree of dominance, and seven types of digenic epistasis. The diallel parents were 15 doubled-haploid lines from a high LD population. The generation mean analysis was based on seven generations, assuming association. Under low LD and no epistasis, the diallel analysis provided confident results about the inheritance of the quantitative trait and high correlation between number of recessive genes and Wr + Vr, but biased estimates of the dominance components and genetic parameters. The additional consequences of high LD under no epistasis were rejection of the additive-dominance model assuming high heritability and lower correlation. Assuming 100% of epistatic genes, for four epistasis types there was evidence of inadequacy of the additive-dominance model. Assuming 30% of epistatic genes, there was a tendency for accepting the additive-dominance model for low heritability traits and for rejecting for high heritability traits. Linkage and epistasis affects the estimates of the genetic components of the generation means. Even assuming 100% of interacting genes, for most epistasis types there was no statistical evidence of epistasis. Assuming positive partial dominance, the signs of the epistatic components do not allow discriminate complementary, recessive, dominant and recessive, duplicate genes with cumulative effects, and non-epistatic genic interaction. Negative epistatic components evidence dominant epistasis. When the additive x additive and dominance x dominance components are positive and the additive x dominance component is negative, there is duplicate epistasis.

Generation Mean Analysis for Yield and Drought Tolerant Traits under Rainfed and Irrigated Conditions in Rice (Oryza sativa L.)

Generation mean analysis was carried out using two crosses, involving a high yielding drought susceptible variety NDR 359 and drought tolerant rainfed cultivars Nagina 22 and Vandana. Six generations namely P1, P2, F1, F2, BC1 and BC2 were grown under both rainfed and irrigated environment to study the gene action for various yield and drought tolerance traits. Scaling test revealed the presence of epistasis for most of the yield and drought tolerance traits in both the crosses. Hence, six parameter model was adopted for these traits and for few traits where epistasis was absent, three parameter model was used. The results revealed that dominance gene effect along with non-allelic interactions had profound effect on the genetic control of majority of the yield traits. Therefore, early generation selection will be misleading for these traits. However, the drought tolerance related traits like proline content and stomatal conductance were governed by additive component as well. Duplicate epistasis was observed for majority of the traits. Hence, present study indicates that, epistasis has a key role in the expression of almost all the traits in both the environment.

Gene Effects and Heritability for Yield Traits in Tomato (Solanum Lycopersicum L.)

Generation mean analysis is a key determinant in designing the appropriate breeding approaches for implementing new desirable character/s in crop varieties and also in studying inheritance of quantitative traits. Parents, F1, F2 and backcrosses exhibited significant digenic interactions in the majority of cross combinations in tomato. Cross combinations and characters indicated the adequacy of simple additive dominance for 50% flowering (CO3 х Floradade, Pant T3 х Azad T5), branches/plant and plant height (CO3 х Floradade, Pant T3 х Kashi Sharad), and fruit/cluster (CO3 х Floradade) indicating absence of non-allelic interactions. Duplicate type of epistasis occurred for 50% flowering (CO3 х Floradade, Kashi Amrit х Kashi Sharad), branches/plant (CO3 х Floradade, Kashi Amrit х Kashi Sharad, Pant T3 х Kashi Sharad), plant height (CO3 х Floradade, Pant T3 х Kashi Sharad), fruit/plant (CO3 х Floradade, Pant T3 х Azad T5, Kashi Amrit х Kashi Sharad, Pant T3 х Kashi Sharad), fruit weight (CO3 х Floradade, Pant T3 х Azad T5), fruit/cluster (Kashi Amrit х Kashi Sharad, Pant T3 х Kashi Sharad), yield/plant (CO3 х Floradade, Punjab Upma х Azad T5, Pant T3 х Kashi Sharad) indicating selection strength should be lenient in the earlier and rapid in later generations because advancement should be through selection. Characters governed by additive components were predominant in fruit/plant and plant height, indicating direct selection for improvement of these traits. Bangladesh J. Bot. 50(3): 453-465, 2021 (September)

Gene Action Studies for Yield and its Related Traits by using Generation Mean Analysis in Mungbean [Vigna radiata (L.) Wilczek]

Background: Mungbean is one of the most important legume crop with high nutritional value and is consumed in various forms in different parts of India. In order to meet its growing demand, there is a need to increase the yield through adoption of breeding approaches like heterosis breeding and breeding for high yielding varieties. This demands a critical study of the gene action involved in regulation of yield and yield attributing traits which can be achieved through generation mean analysis. Methods: In the present study, generation mean analysis was undertaken using five parameter model to estimate the nature and magnitude of gene action of yield and its component traits in six crosses of greengram. Result: Magnitude of dominance gene effect was reported to be higher than additive gene effect in most of the crosses. Either one or both the interaction components were found significant for all the traits besides number of branches per plant and hundred seed weight. It was evident from the study that the yield components could be improved by exploiting both additive and non-additive gene effects. The transgressive segregants thus produced will prompt the development of desirable high yielding genotypes.

​Generation Mean Analysis for Seed Yield and Its Contributing Traits in the Inter-varietal Cross of Blackgram [Vigna mungo (L.) Hepper]

Background: Blackgram is being cultivated as an indispensable pulse crop and a rich source of vitamins and minerals. Though the requirement for blackgram is high, the productivity is low. The ultimate aim of any plant breeder in a crop improvement program is to increase seed yield/ productivity. With this background, the current study was focused to investigate genetic variability/effects on important yield and its contributing traits of blackgram. Methods: The research material comprised of P1, P2, F1, F2 and F3 obtained from a cross between CO 6 and LBG 17 varieties in blackgram. Observations on nine biometrical traits were recorded from all these five populations for generation mean analysis. By employing Mather and Jinks (1971) scaling test of C and D, the suitability nature of the simple additive-dominance model can be identified. Following Hayman (1958) perfect fit solution, the mean of five generations (P1, P2, F1, F2 and F3) was utilized to calculate five parameters. Result: Fitted genetic model revealed as important yield and yield contributing traits governed by dominance and epistasis in this study, it indicates the selection may be postponed to later generations with greater homozygosity.

Genetic Variance Components in Cotton by Generation Mean Analysis

The mode of gene action for the expression of quantitative traits is decided by the predominance of variances due to additive, dominance and epistasis gene effects. In this experiment, involving four F1 crosses (TCH1716 x TCB37, TCH1705-101 x TCB209, KC2 x TCB26 and TSH0250 x DB3) of upland cotton, inheritance of major yield components by Generation Mean Analysis was investigated. The investigation revealed that both additive and dominance gene effects were involved in the expression of most of the yield contributing traits. One or more types of epistatic interaction effects were prevalent for all the characters and thus played a major role in the control of the characters. The inheritance of the traits was found to be complex in lieu of the low heritability estimates and genetic advance over mean. For seed cotton yield per plant, the dominance x dominance interaction effect was positively significant for all the crosses, the additive x dominance effect was positively significant only in cross 1 and the dominance main effect showed negative significant in all crosses. The dominance (h) and dominance x dominance (l) effects were of opposite signs in all the crosses indicating the presence of duplicate epistasis in all the crosses. To harness additive gene effects for improvement of some of the traits, breeding methods with postponement of selection to later generation should be adopted.