Genetic combining, heterosis analysis for horticultural traits in tomato (Solanum lycopersicum L.) using ToLCV-resistant lines and molecular validation of Ty genes

Tomato is a pivotal vegetable crop worldwide concerning human nutrition, economy and in service to biotechnology. Tomato leaf curl virus (ToLCV) is a begomovirus transmitted through the whitefly (Bemisia tabaci) and is responsible for severe losses in tomato production. In this context, the current investigation was carried out to determine heterotic combiners with high yield, resistance to ToLCV and mode of gene action for economically important traits. For this, 11 prescreened inbred lines were crossed in a half diallel fashion to generate 55 F1 hybrids. The 55 crosses with 11 parents and commercial checks were evaluated for different horticultural traits and resistance to ToLCV. The molecular validation with SCAR markers TG0302 and SCAR1 confirmed the presence of ToLCV-resistant genes in parents and their crosses. The hybrid IIHR-2902 × IIHR-2852 showed the presence of both Ty-2 and Ty-3 alleles in the homozygous state. The estimation of σSCA2 and σGCA2 was significant. It also indicated that the genetic control of target traits was under additive and non-additive gene effects. The values of σA/D2 along with σGCA2/σSCA2 found to be less than unity indicates the preponderance of non-additive gene action in the expression of the studied traits except for percent disease incidence. The parental line IIHR-2919 was the best combiner for fruit and yield traits. The cross combinations IIHR-2913 × IIHR-2898 exhibited significantly higher economic heterosis for yield along with the presence of Ty-2 and Ty-3 genes. The study paves the way for breeding high yielding and ToLCV-resistant hybrids in tomato.

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.

Genetic parameters controlling the inheritance of glaucousness and yield traits in bread wheat

Wheat breeders frequently use generation mean analysis to obtain information on the type of gene action involved in inheriting a trait to choose the helpful breeding procedure for trait improvement. The present study was carried out to study the inter-allelic and intra-allelic gene action and inheritance of glaucousness, earliness and yield traits in a bread wheat cross between divergent parents in glaucousness and yield traits; namely Mut-2 (P1) and Sakha 93 (P2). The experimental material included six populations, i.e. P1, P2, F1, F2, BC1, and BC2 for this wheat cross. A randomized complete block design with three replications was used, and a six parameters model was applied. Additive effects were generally more critical than dominance for all studied traits, except for plant height (PH) and grain yield/plant (GYPP). The duplicate epistasis was observed in spike length; SL, spikes/plant; SPP and days to heading; DTH. All six types of allelic and non-allelic interaction effects controlled SL, GYPP, DTH and glaucousness. All three types of epistasis, i.e. additive x additive, additive x dominance, and dominance x dominance, are essential in determining the inheritance of four traits (SL, GYPP, DTH and glaucousness). Dominance × dominance effects were higher in magnitude than additive × dominance and additive × additive in most traits. The average degree of dominance was minor than unity in six traits (glaucousness, grains/spike, spike weight, days to maturity, 100-grain weight and SL), indicating partial dominance and selection for these traits might be more effective in early generations. Meanwhile, the remaining traits (PH, SPP, GYPP and DTH) had a degree of dominance more than unity, indicating that overdominance gene effects control such traits and it is preferable to postpone selection to later generations. The highest values of narrow-sense heritability and genetic advance were recorded by glaucousness trait followed by SL and SPP, indicating that selection in segregating generations would be more effective than other traits.

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.

Genetic studies of different agronomic, quality and yield contributing traits in Gossypium hirsutum L.

An experiment of 4 × 4 diallel was carried out to study the gene action of different yield and yield contributing traits of four advanced cotton cultivars using Mather and Jinks approach. Significant variation was present for all the characters (P< 0.01). The data on recorded parameters revealed that most of the traits were fully or partially fit for genetic interpretation. Additive gene action (D) was significant and pre-dominant for all the characters while seeds per locule showed dominance effect of H1& H2, and it was confirmed by the value of degree of dominance (H1/D 0.5). The value of H2/4H1 and h2 (measures the direction of dominance) demonstrated asymmetrical division of dominant genes for all traits, except ginning out turn (G.O.T) percentage and fiber length, in parental material. All the studied traits showed high value of narrow sense heritability (h2NS), however seeds per locule possessed low heritability. The genetic analysis revealed that all the characters could be improved by progeny and pedigree selection, whereas hybrid dynamism could be exploited in the trait like seeds per locule.