Specific Combining Ability Variance Research Articles

A 7×7 diallel cross for developing high-yielding and saline-tolerant barley (Hordeum vulgare L.)

In this experiment, F1s produced from a 7 × 7 half-diallel cross along with their parents were evaluated to develop high yielding and saline-tolerant barley lines. The investigation focused on the general combining ability (GCA) of parents, specific combining ability (SCA) of offspring, genetic action, and heterosis of eight quantitative variables. Genetic analysis and potence ratio suggested that different degrees of dominance controlling the inheritance of the studied traits. Significant GCA and SCA variances suggested the presence of both additive and non-additive gene actions controlling the traits. However, a GCA:SCA ratio lower than 1 indicated the preponderance of the non-additive gene action involved in the expression of the traits. The parents P5 and P6 possess the genetic potential favorable for early and short stature in their F1s. Conversely, P2 and P4 were more likely to produce short F1s with high yield potential. Based on the mean performance, SCA, and heterobeltiosis, crosses P2 × P3, P2 × P7, P3 × P4, P4 × P5, P5 × P6, and P6 × P7 were selected as promising F1s for earliness, short stature, and high yield potential. These crosses are recommended for further breeding to obtain early-maturing and high-yielding segregants. To identify saline-tolerant F1s, screening was conducted in saline media prepared in half-strength Hoagland solution. The salinity stress involved exposing F1s to 100 mM NaCl for first 10 days, and followed by an increase to 150 mM until maturity. Among the F1s, five crosses (P1 × P2, P2 × P3, P3 × P5, P4 × P6, and P4 × P7) exhibited promising signs of saline tolerance based on a comprehensive evaluation of healthy seed set, K+/Na+ ratio, root volume, generation of reactive oxygen species (O2•− and H2O2), and activities of key antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR). These crosses will undergo further evaluation in the next filial generation to confirm heritable saline tolerance.

Field Insights into the Genetic Symphony: Decoding Gene Dynamics for Enhanced Sorghum Yield (Sorghum bicolor [L.] Moench)

In this investigation using line × tester analysis, fifteen parents (3 Cytoplasmic Male Sterility females and 12 males) and 36 hybrids, including the standard check CSH-25, underwent evaluation in a randomized block design with three replications. Notably, significant general combining ability variances for 1000-seed weight and highly significant specific combining ability variances for all traits were observed. The research highlights the prevalence of additive genetic variance in 1000-seed weight and the combined influence of additive and nonadditive gene effects in panicle length ratio. Recognized good general combiners, such as SR 2991 , SR 2950 , SR 2872, SR 2984 and 691A, provide valuable insights for breeding strategies. Subsequent evaluations of promising hybrids, particularly 691 A × SR 2991, 691 A × SR 2872 and 691 A × SR 2950 hold potential for optimizing grain yield, panicle length, and dwarfness. These findings provide nuanced insights for future Sorghum breeding programs, enhancing understanding of gene dynamics for improved productivity and emphasizing the pivotal role of hybrid sorghum in contemporary agricultural contexts.

Combining ability analysis in bitter gourd (Momordica charantia L.) for potential quality improvement.

Combining ability analysis provides useful information for the selection of parents, also information regarding the nature and magnitude of involved gene actions. Crops improvement involves strategies for enhancing yield potentiality and quality components. Targeting the improvement of respective characters in bitter gourd, combining ability and genetic parameters for 19 characters were estimated from a 6×6 full diallel analysis technique. The results revealed that the variances due to general combining ability (GCA) and specific combining ability (SCA) were highly significant for most of the important characters. It indicated the importance of both additive and non-additive gene actions. GCA variances were higher in magnitude than SCA variances for all the characters studied indicating the predominance of the additive gene effects in their inheritance. The parent P2 (BG 009) appeared as the best general combiner for earliness; P1 (BG 006) for number of fruits, average single fruit weight and fruit yield; P4 (BG 027) for node number of first female flower and days to seed fruit maturity; P3 (BG 011) for fruit length and thickness of the fruit flesh; P5 (BG 033) for 100-seed weight; and P6 for number of nodes per main vine. The SCA effect as well as reciprocal effect was also significant for most of the important characters in different crosses.

Effects of Different Treatments on Seed Germination and Breaking Seed Dormancy in Wild Luffa Species

Comprehending general combining ability (GCA) and specific combining ability (SCA) is pivotal in maize breeding for successful hybrid development. GCA signifies the overall genetic worth of a parent, while SCA demonstrates unique interactions between parents. In instances where GCA variances surpass SCA variances, early assessments become more effective, enabling the anticipation of superior hybrids based on parental GCA impacts. Assessing the combining ability of maize becomes increasingly crucial with escalating temperatures, which can adversely affect maize growth and crop yield. Research conducted in Prayagraj involved utilizing 7x7 half diallel crosses of maize initially developed during the Rabi 2022 season, followed by their subsequent planting in a randomized block design (RBD) during spring 2023. The primary aim of the study was to evaluate the general combining ability (GCA) and specific combining ability (SCA) effects exhibited by the parents and hybrids, respectively, in order to identify superior-performing parents and hybrids among them. The results showcased strong positive GCA in MILCT-145F (P7) and MILC-2050 (P6), while specific heat-tolerant hybrids, such as P7xP1, P6xP2 exhibited outstanding performance in grain yield and other associated traits.

Analysis of Genetic Architecture for Ten Genotypes of Bread Wheat Using Half Diallel Crosses Under Nitrogen Stress

This study included 10 genotypes of bread wheat are M45, Yakora, Giza168, Sids 12, SK95, Misr2, Giemiza 9, Sahel 1, Sids14, and Silano. The genotypes (parents and F1 crosses) were cultivated at the research station of the Department of Field Crops of the College of Agriculture at the University of Kirkuk, during the season (2021-2022) in two separate experiments on sufficiency and insufficiency of the nitrogen element using a Randomized Complete Block Design (R.C.B.D) and with three replications, to estimate the general and specific combining ability, gene action and some genetic parameters. The results of the statistical and genetic analysis showed that there are highly significant differences for the general and specific combining ability values and that the ratio of the combining ability variance components to the specific combining ability variance components was less than the one for nitrogen sufficiency and insufficiency for all the studied traits. Sids14 variety excelled in its desirable effects of general combining ability, followed by Sr. (Sids12). The hybrid (M45 × Sids14) had the highest desired values for the effects of the special combining ability at nitrogen levels for all the traits studied, followed by the cross (Sahel 1 × Sids 12) also for all the traits studied except for The number of spikes plant-1 when there was insufficient nitrogen. The heritability broad sense was high with sufficient and insufficient nitrogen, while heritability narrow sense was high with sufficient nitrogen in the number of grains spike-1 and grains yield plant-1 (gm) and medium in The number of spikes plant-1 and the weight 1000 grains (gm) and the biological yield in the insufficient amount of the nitrogen element, the heritability narrow sense was medium in all studied traits. The average degree of dominance was greater than one when nitrogen was sufficient and insufficient, which indicates the existence of Over dominance, and the expected genetic advance as a percentage was low except for the number of grains spike-1 when nitrogen was sufficient and the grains yield plant-1 (gm) when nitrogen was insufficient, as it was medium. (11.908 and 12.250), respectively, these parents that are superior in the general combining ability with high phenotypic significance can be included in wheat breeding programs to produce hybrids that are superior in the specific combining ability that can be invested in the following generations with in the breeding programs to reach the best promising varieties with future nitrogen insufficiency.

Heterosis and combining ability estimates for okra (<i>Abelmoschus esculentus</i> L. Moench) varieties for yield attributing characters in Sudan savanna of Nigeria

Two location trials were conducted at the Teaching and Research Farm of the University of Maiduguri and screen house of the Faculty of Agriculture during 2018/2019 dry season to estimate the combining ability variance, general combining ability (GCA) effects of parents and specific combining ability (SCA) effects of crosses with six okra genotypes. They include: three improved varieties NHAe 47-4, LD-88, Clemson spineless and three locals, Chalawa, Syria and Sola, crossed in a 3 x 3 line x tester mating design to generate nine F1 hybrids. All the F1s along with their parents were evaluated in a Randomized Complete Block Design (RCBD) and Completely Randomise Design (CRD), with 3 replications. Positive heterosis were observed for number of fruits per plant in the crosses Chalawa x NHAe47-4, Chalawa x Clemson Spineless, this directly indicated their important contributions toward total fruit yield in okra. The variance of GCA and SCA revealed that both additive and non-additive gene actions were important in the control of most agronomic.The ratio of GCA/ SCA indicates greater preponderance of non-additive gene action for the characters in all the traits except number of leaves per plant and days to 50% flowering which were controlled by additive gene actions. The parent Syria was the overall best general combiner among the lines for all characters in the field and Chalawa was the overall best general combiner for all characters measured among lines in the screen house. LD88 recorded the highest GCA effects for all of the characters among testers in both experiments. Similarly, in the field, the hybrid Sola x NHAe47-4 recorded the maximum SCA effect for all characters except days to 50% flowering; Syria x NHAe47-4 was the best SCA for most characters except plant height and also the cross between Syria x Clemson Spineless was the best SCA for most characters except number of fruits per plant. In the screen house, the cross between Chalawa x NHAe47-4, showed superior SCA for all characters measured. Appreciable level of heterosis was observed for most of the characters studied, the overall maximum positive significant heterosis for total fruit yield (kg/ha) was observed in crosses Syria x LD88 (52.80) and Chalawa x NHAe47-4(123.30) over better parents. The preponderance of non-additive genetic effect and the tremendous level of heterosis observed among the characters in the parents and their crosses studied would be great asset in choosing the okra varieties for intercrossing and development of hybrids varieties for commercial production of okra.

Hybrid Vigour and Combining Ability in Biofortified Maize (Zea mays L.)

The study was conducted during winter season of 2020–2021 and rainy season of 2021 at Maize Research Station, Sardarkrushinagar Dantiwada Agricultural University, Bhiloda, Gujarat, India. The aim of the study was to assess magnitude of heterosis and combining ability of forty-five single cross hybrids developed by half-diallel mating design involving ten parents and two standard checks. The field experiment was laid out in randomized block design with three replications. The heterosis, combining ability and components of genetic variance were studied for diverse thirteen characters. The analysis of variance revealed that mean square values of genotypes were significant for all the characters which indicated the existence of considerable amount of genetic variation in genotypes for all the characters. Among single crosses, IMR-76×IMR-58 exhibited maximum mean and desired SCA effect and standard heterosis for β-carotene and IMR-53×IMR-72 for kernel yield. The general and specific combining ability variances observed highly significant for all traits except days to tasseling (only additive gene action), anthesis-silking interval and shelling percentage (only non-additive gene action). The σ2A/σ2D ratio indicated that preponderance of non-additive gene action for the inheritance of these characters suggesting due weightage should be given to heterosis breeding for genetic improvement of these traits. The crosses namely IMR-52×IMR-72 and IMR-51×IMR-58 presented significant heterosis for days to maturity, grain yield, iron and β-carotene content.

Combining Ability Studies on Yield and Yield Related Traits in Tomato (Solanum lycopersicum L.)

Aim: The present study was conducted to generate information regarding the general combining ability (GCA), specific combining ability (SCA), genetic parameters and GCA and SCA variances in tomato.
 Study Design: The parents and F1s were laid out in Randomized block design with 3 replications.
 Place and Duration of Study: The present study was conducted at research farm of Banaras Hindu University, Varanasi. Crosses were generated in Line x Tester design and resultant F1, F2 and parents were evaluated.
 Methodology: After genetic diversity evaluation, ten genotypes were selected and used as females which were crossed with three other selected genotypes used as males in Line × Tester mating design followed by evaluation of their F1 hybrids along with parents.
 Results: The study concluded that Pant T-3 was a good general combiner for plant height, days to 50% flowering and days to first fruit set, Kashi Amrit was a good general combiner for number of primay branches/plant, CO-3 was a good general combiner for number of flower clusters/plant, number of flowers/cluster and number of fruits/plant, H-86 was a good general combiner for number of fruits/cluster, Fla 7171 was a good general combiner for fruit length, fruit width and fruit weight. Based on sca effects best specific combiner for plant height and fruit yield was Punjab Upma × Azad T-5. The ratio of σ2gca/σ2sca is less than unity for all characters except fruit shape index which also indicated the preponderance of non additive genetic variance. High heritability (>60%) combined with high genetic advance (>20%) was observed for fruit yield, number of primary branches/plant, plant height, number of flower clusters/plant, number of flowers/cluster, fruit weight, number of fruits/cluster, number of fruits/plant. These traits can be improved by simple selection in tomato breeding programme.
 Conclusion: From the study it was concluded that best general combiners for various yield and yield related traits were Pant T-3, Kashi Amrit, CO-3, H-86 and Fla 7171. Based on sca best specific combiner for plant height and fruit yield was Punjab Upma × Azad T-5.

Combining ability analysis of newly developed male lines of castor (Ricinus communis L.) in Rajasthan

Genetic parameters of 50 castor hybrids developed using 10 newly developed male inbred lines and 5 stable pistillate lines were estimated in a line x tester design. Analysis of combining ability depicted significant mean sum of squares for both general combining ability (GCA) and specific combining ability (SCA) for all the characters which indicated the presence of both additive and non-additive gene actions. The high amount of s 2 SCA and ratioof GCAto SCA variances near to zero indicated that the dominance gene effect was predominant in newly developed lines for all the characters under study. The highest positive gca effect was exhibited by MCP-1-1, for seed yield and number of capsules on primary raceme, effective length of primary raceme and height up to primary raceme. SKP-84 was also good general combiner for traits such as 100-seed weight, number of capsule on primary raceme, nodes to primary raceme and height up to primary raceme. Among the male parents, MP-11-17 was found the best general combiner for cumulative seed yield, raceme length and number of capsule. Cross M-574 x MP-17-17 was identified as the best cross for cumulative seed yield followed by MCP-3 x MP-7-17 and SKP-84 x MP-11-17. These combinations of crosses would be useful in breeding programme for improvement in cumulative seed yield of castor.

Genetic variability predicting breeding potential of upland cotton (Gossypium hirsutum L.) for high temperature tolerance

BackgroundHigh temperature stress at peak flowering stage of cotton is a major hindrance for crop potential. This study aimed to increase genetic divergence regarding heat tolerance in newly developed cultivars and hybrids. Fifty cotton genotypes and 40 F1 (hybrids) were tested under field conditions following the treatments, viz., high temperature stress and control at peak flowering stage in August and October under April and June sowing, respectively.ResultsThe mean squares revealed significant differences among genotypes, treatments, genotype × treatment for relative cell injury, chlorophyll contents, canopy temperature, boll retention and seed cotton yield per plant. The genetic diversity among 50 genotypes was analyzed through cluster analysis and heat susceptibility index (HSI). The heat tolerant genotypes including FH-Noor, NIAB-545, FH-466, FH-Lalazar, FH-458, NIAB-878, IR-NIBGE-8, Weal-AG-Shahkar, and heat sensitive, i.e., CIM-602, Silky-3, FH-326, SLH-12 and FH-442 were hybridized in line × tester fashion to produce F1 populations. The breeding materials’ populations (40 F1) revealed higher specific combining ability variances along with dominance variances, decided the non-additive type gene action for all the traits. The best general combining ability effects for most of the traits were displayed by the lines, i.e., FH-Lalazar, NIAB-878 along with testers FH-326 and Silky-3. Specific combining ability effects and better-parent heterosis were showed by the crosses, viz., FH-Lalazar × Silky-3, FH-Lalazar × FH-326, NIAB-878 × Silky-3, and NIAB-878 × FH-326 for seed cotton yield and yield contributing traits under high temperature stress.ConclusionHeterosis breeding should be carried out in the presence of non-additive type gene action for all the studied traits. The best combiner parents with better-parent heterosis may be used in crossing program to develop high yielding cultivars, and hybrids for high temperature stress tolerance.

English

Twenty-one crosses developed from the frame of line × tester analysis along with ten parents were grown in two replicates experiment. Data on days to flowering, days to maturity, plant height, number of pods/plant, number of primary branches, number of secondary branches, number of tertiary branches, number of seeds per pod and seed yield per plant (g), revealed high significant differences exist among lines, testers and crosses for all traits studied. The ratio value of general combining ability variance to specific combining ability variance suggests the preponderance of non-additive type as well as additive gene action for some traits. Genotype Pusa-362 was the best general combiner for days to flowering. Genotype ICCL-87322 was identified as the best general combiner for the number of seeds per plant. Genotype BG329 was identified as the best general combiner for seed yield per plant (g) followed by KPG-59. Genotype PG-92-4 recorded desirable and significant GCA across five traits consistently. Cross PG-92-4 X Pant-186 recorded five significant SCA in the positive direction for secondary branches, number of tertiary branches, number of pods per plant, seed yield per plant and hundred seed weight. This cross is considered the most important compared to other materials under study. The proportional contribution of line × tester interaction was evident for most of the traits followed by the contribution of maternal lines. Days to flowering, days to maturity, primary branches, secondary branches, tertiary branches, pod per plant, seed per pod and seed yield per plant (g) recorded higher SCA variance suggesting non-additive gene action exit in expressing of these traits. The presence of a high SCA effect suggests that heterosis breeding can be exploited. Selection for those characters should be undertaken in later generations when these traits are fixed in homozygous lines. Key words: Chickpea, Cicer reticulatum, combining ability, gene action, heritability.

Heterosis and Combining Ability Estimate on Yield and Yield-Related Traits in a Half Diallel Crosses of Kenaf (Hibiscus Cannabinus L.) in Malaysia

ABSTRACT Understanding heterosis and combining ability among distinct kenaf (Hibiscus cannabinus L.) genetic resources is crucial for developing hybrid kenaf. An investigation was conducted on 36 F1 combinations produced from nine parental genotypes of kenaf in a diallelic scheme using Griffing diallel analysis technique 2, model I. Highly significant F-test values revealed the presence of variability for all the 15 quantitative traits for general combining ability (GCA) and specific combining ability (SCA) except days to 1st flowering. The magnitude of GCA variance was considerably higher than that of SCA variance for plant height, stem middle diameter, stem top diameter, days to flowering, number of pods, number of seeds and 1000 seeds weight, showing the predominates of additive gene for these traits. Narrow-sense heritability of 50.93% in the combined environments showed that seed number was the most heritable trait, whereas days to 1st flowering and 1000 seed weight had moderate heritability. Parents P1, P3 and P4 had the most dominant alleles for most traits studied. Considering SCA and heterosis values, the hybrids H3, H4, H9, H11, H23, H29 and H35 had high heterotic for fiber and seed yield.

Combining Ability and Heterosis Study for Grain Yield And Yield Contributing Traits of Maize (Zea Mays L.)

The nature of combining ability and heterosis were studied in an 8×8 diallel cross excluding reciprocals in maize for grain yield and yield contributing characters. Significant estimates of general combining ability (GCA) and specific combining ability (SCA) variances suggested the importance of both additive and non-additive gene actions for the expression of the traits studied. The variances for GCA Was found significant for days to pollen shedding, days to silking, plant height, ear height, 1000- grain weight and yield. SCA was significant for all the characters except yield. Non-significant SCA variance for yield suggests that this trait was predominantly controlled by additive type of gene action. Variances due to GCA were much higher in magnitude than SCA for all the characters indicating preponderance of additive gene effects for the inheritance of these traits. Parents CML431 (P4) and CML285 (P6) were the best general combiner for both high yield and parent CLG1837 (P7) and CML429 (P8) for earliness and dwarf plant type. Seven crosses CL02450×CML451 (P1×P5), CL02450×CLG1837 (P1×P7), CML551×CML431 (P2×P4), CML223×CML451 (P3×P5), CML431×CML451 (P4×P5), CML431× CML429 (P4×P8) and CML285× CLG1837 (P6× P7) exhibited positive SCA effects for grain yield. Considering, BARI Hybrid Maize-9 (BHM-9) as check, the percent heterosis for grain yield varied from -46.17 to 12.14%. Two crosses CML551×CML431 (P2×P4) and CML285× CLG1837 (P6× P7) exhibited significant and positive heterosis 12.14 and 10.77%, respectively over the check BHM-9 suggested their benefit cost ratio (BCR) study for developing high yielding hybrid varieties.
 Bangladesh J. Agril. Res. 47(1): 81-90, March 2022

Exploitation of combining ability and heterosis potential for improvement in okra (Abelmoschus esculentus) genotypes

The present investigation was undertaken with the objective to carry out combining ability and heterosis for 13fruit yield and its attributing traits in 14 parents and their 24 crosses in okra (Abelmoschus esculentus (L.) Moench)at vegetable research farm, CCS Haryana Agricultural University, Hisar, Haryana during spring-summer season2019–20 and rainy (kharif) season 2020–21. Four crosses, viz. HB-20-3-4 × Hisar Naveen (HN), Hisar Mutant (HM)-1× Hisar Unnat (HU), HBMS-1 × Hisar Unnat (HU) and HB-76-2-4 × Hisar Naveen (HN) showed highly significantpositive economic heterosis for yield and its contributing traits.Parents HB-20-3-4 and HM-1 were found to be thebest general combiner for most of the economic traits. While, cross HB-60-1 × HN followed by HBMS-1 × HU, HB-20-3-4 × HN, HM-1 × HU and HB-96-2 × HU demonstrated strong SCA effects for yield and its attributes. The ratio of general combining ability (σ2GCA) and specific combining ability variances (σ2SCA) was less than one for all the quantitative traits indicating the non-additive gene effects predominated in determining the expression of allthese characters and demonstrates variability in genotypes, which provide ample scope for improvement of yield and its contributing traits in okra. Line HB-60-1 when crossed with Hisar Naveen, and HBMS-1 with Hisar Unnat gavesuperior hybrids as compared to other crosses. Hence, these parents can be exploited for further genetic improvement programmes and isolation of desirable segregants in okra.

Heterosis and Combining Ability Studies in A 5x5 Diallel Crosses of Maize Inbred Lines

The present study was conducted to evaluate the genetic architecture of five diverse maize genotypes using combining ability analyses. General combining ability (GCA) mean squares were non-significant for grain yield and its related components. Specific combining ability (SCA) mean squares were highly significant for grain yield, the number of grains per row and cob girth while non-significant for days to tasseling, days to silking, plant height, cob height and cob length. These studies suggested the preponderance of non-additive type of gene action for grain yield, cob girth and number of grains per row and additive gene action for days to tasseling, days to silking, plant height, cob height and cob length. The genotypes MIL2020-51 and MIL2020-52 were good general combiners for grain yield, grains per row, cob height and plant height. These lines were the poorest general combiner for days to 50% tasseling and days to 50% silking which suggested that these genotypes had sufficient genes for inducing earliness. The crosses MIL2020-51 x MIL2020-54, MIL2020-52 x MIL2020-53, MIL2020-51 x MIL2020-55, MIL2020-53 x MIL2020-55and MIL2020-52 x MIL2020-55 were the best performing combinations for grain yield. These crosses involved good x good and good x poor general combiners. The reciprocal cross combinations MIL2020-55 x MIL2020-53, MIL2020-52 x MIL20220-51, MIL2020-54I x MIL2020-52, MIL2020-55 x MIL2020-51, MIL2020-54 x MIL2020-51and MIL2020-55 x MIL2020-54 showed large positive estimates for grain yield suggesting that cytoplasmic inheritance also had a role in the expression of grain yield. SCA variances were higher than GCA variances for grain yield, plant height, cob height, number of grains per row, cob girth and cob length which highlighted major role of non-additive genes in the inheritance of these traits. Additive gene action was found more important for number of days to 50% tasseling and number of days to 50% silking

Study of combining ability analysis on half diallel crosses in water stress of wheat (triticum aestivum L.)

Combining ability analysis was performed in a 10 x 10 half diallel cross of ten bread wheat genotypes for yield and its contributing traits. The experiment was conducted in 2013–2014 and 2014–2015 at Crop Research Centre, Sardar Vallabhbhai Patel University of Agriculture & Technology, Modipuram, Meerut, UP. Combining ability revealed that both general and specific combining ability variances were responsible for all the traits. Thus, additive and non-additive gene action was important in controlling the inheritance of all the traits. The variance due to gca was equal to that part of genetic variance which is due to additive and additive x additive effects, while variances due to sca was ascribed to non-additive components of variance that include dominance and epistatic variance. On the basis of overall gca effects, the best general combiners were WH-147, RAJ-3765, WH-730, NP-846, HUW-468, UP-2382 for maximum number of characters under normal and water stress condition. On the basis specific combining ability effects, five crosses viz., HUW-234 x RAJ-3765, HUW-234 x HUW468, WH-730 x C-306, C-306 x HD-2967 and DBW-17 x UP-2382 in normal condition, and WH-147 x WH-730, WH-147 x HD-2967, RAJ-3765 x HUW-468, RAJ-3765 x WH-730 and WH-730 x UP-2382 in water stress condition were found as good specific combiner for grain yield per plant.

Genetic analysis of maize grain yield components and physiological determinants under contrasting nitrogen availability

Context Most maize breeding is conducted under high-input conditions, with nitrogen supply being crucial due to its impact on yield. Aims This study aimed to investigate broad-sense heritability, and general and specific combining ability variances of physiological traits defining grain yield under contrasting soil nitrogen supply. Methods A six-parent full diallel cross was analysed under high (fertilised with 200 kg N/ha) and low (unfertilised control) nitrogen supply in two seasons. We measured kernel number per plant and kernel weight, the associated traits of plant growth during the critical and grain-filling periods, and source–sink relationships in both periods. Key results Heritabilities of traits ranged from 0.54 to 0.88, and general surpassed specific combining ability for most traits. At low nitrogen (1) the relative importance of general combining ability estimated by Baker’s ratio increased across traits (low nitrogen: 0.90 vs high: 0.85) because the decrease in combining ability variance was larger for specific than general (–78% vs −39%), and (2) source–sink relationship during grain filling had the highest Baker’s ratio (0.96) and heritability (0.78). Plant growth rates during the critical period and kernel number increased substantially at high nitrogen (40 and 34%, respectively), and they had the highest heritability (0.79 and 0.88) and Baker’s ratio (>0.90). Conclusions Low nitrogen environments increased the relative importance of general combining ability effects, and high yield can be obtained by improving the source–sink relationship during grain filling, whereas high nitrogen increased yield by improving plant growth rate during the critical period and kernel number. Implications Knowledge of source–sink relationship during effective filling period, plant growth during the critical period and kernel number may result in a more targeted selection program.

Estimation of Combining Ability in F2 Hybrids of Bread Wheat (Triticum aestivum L.) Genotypes

The seed of 6 parental cultivars along with 15 F2 Hybrids of hexaploid wheat was planted in randomized complete block design with three replications 6 x 6 half diallel during 2016-2017 sat Southern Wheat Research Station, ARI, Tandojam, Sindh, Pakistan. Mean squares due to General Combining Ability (GCA) and Specific Combining Ability (SCA) variances were highly significant and significant for all morphological traits. It was noticed that additive, as well as nonadditive genes, were there for GCA and SCA. SCA variances were observed greater than those of GCA variances for five traits (PH, TPP, SL, SPS, GYPP) displaying the predominance of nonadditive genes, for some of the characters, nonetheless, GCA variances were more for the rest of the characters (GPS, TGW). Parental cultivars such as Khirman displayed maximum positive and desirable GCA effects for spike length and grains spike-1, Hamal for tillers plant-1 and spikelets spike-1 and Benazir and NIA-Sarang for grain yield plant-1 and seed index. On the other hand, Hamal and NIA-Sarang equally distributed negative, but desirable GCA effects for plant height. The SCA estimates revealed that Sindhu x Hamal manifested maximum positive estimates for spike length and grain yield plant-1, whereas Benazir x Sindhu was found as the best specific combiner for spikelets spike-1 and seed index, Benazir x Khirman and Benazir x NIA-Sarang for tillers plant-1 and grains spike-1. These F2 hybrids may be the best choice as a breeding material for hybrid crop development to improve yield characters. Therefore, it may be possible to take advantage of better general and specific combiners to further selection for the development of a hybrid variety of wheat which can assist to enhance the total production in Pakistan.

Combining ability analysis of newly developed monoecious lines of castor (Ricinus communis L.) in Rajasthan

Genetic parameters of 50 castor hybrids developed from 10 newly developed monoecious lines and 5 stable pistillate lines were estimated in line x tester design. Analysis of combining ability depicted significant mean sum of squares for both general combining ability (GCA) and specific combining ability (SCA) for all the characters which indicated the presence of both additive and non-additive gene actions. The high amount of s 2 SCA and ratio of GCA to SCA variances near to zero indicated that the dominance gene effect was predominant in newly developed lines for all the characters under study. The highest positive gca effect was exhibited by MCP-1-1, for seed yield and number of capsules on primary raceme, effective length of primary raceme and height up to primary raceme. SKP-84 was also a good general combiner for 100 seed weight, number of capsules on primary raceme, nodes to primary raceme and height up to primary raceme. Among the male parents, MP-11-17 was found the best general combiner for cumulative seed yield, raceme length and numbers of capsules. Cross M-574 x MP-17-17 was the best cross for cumulative seed yield followed by MCP-3 x MP-7-17 and SKP-84 x MP-11-17. These combinations would be useful in breeding programme for improvement in seed yield of castor.

Combining Ability for Quantitative Traits Under Normal And Heat Stress Conditions in Maize (Zea Mays L.)

Investigation was carried out to ascertain the genetic architecture for heat tolerance and yield components from diallel crosses in maize (Zea mays L.). The combining ability in both the normal and heat stress conditions revealed highly significant mean squares due to general combining ability (GCA) and specific combining ability (SCA) in both the direct and reciprocal crosses for all the characters except for anthesis-silking interval in normal condition of the reciprocal crosses. Estimate of components of variance for 13 characters revealed higher SCA variance than that of GCA and reciprocal crosses for all the characters. CML 411 was good general combiner for grain yield in both the conditions, whereas, CML 306 and CML 307 were good general combiners in heat stress condition, and CML 164, CML 304 and CML 305 were average general combiners in normal condition. On the basis of high yield, high SCA and at least high GCA of seed parent, the CML 411*CML 305 and CML 411*CML 307 were identified as promising hybrids for normal and heat stress conditions, respectively. Bangladesh J. Bot. 50(3): 659-669, 2021 (September)