Non-additive Gene Action Research Articles

Combining Ability of Indonesian Tropical Maize in Two Different Seasons

Testing an inbred cross for hybrid development requires a proper test cross method. The diallel is one crossing method to find out the magnitude of inbred combining ability, both general general (GCA) and specific combining ability (SCA) and specific combining ability, that is useful in hybrid development. The objective of the study is to determine the GCA, SCA and heterosis of 6 inbred lines in two seasons. All the inbreds were crossed in diallel design and further evaluated for their combining ability and genetic ratio following the respective methods of Griffing and Baker. The results revealed that GCA, SCA and Reciprocal (REC.) were influenced by planting seasons for almost all yield and yield-related traits. Non-additive gene action was more important in controlling ear length, ear row number, shelled ear weight and yield. The best GCA for yield trait was detected on inbreds G2 and G5. The conclusion from the interpretation of both SCA and REC. is that the inbred crosses of G1 x G6, G2 x G5, G4 x G6, and G5 x G6 have the best yields followed by high heterosis values.

Evaluation and Classification of Yellow Maize Inbred Lines Using Line X Tester Analysis Across Two Locations

Ten yellow maize inbred lines and three testers were top crossed in line × tester scheme in 2019 season. The resulted 30 top crosses with two check hybrids were evaluated at two locations in 2020 growing season to assess mean performance, general and specific combining ability and their interaction with locations as well as elucidate type of gene action. The recorded data were days to 50% silking, plant height, ear height, ear length, ear diameter, No. of rows/ear, No. of kernels/row and grain yield (ardab/fed). The results showed that, the mean squares due to locations (Loc), genotypes (G), crosses (Cr.), G × Loc and Cr. × Loc interactions were significant for all the studied traits. Highly significant differences were observed among the evaluated lines (L), testers (T) and its corresponding hybrids for all traits. non-additive gene action gave an important role in the inheritance of all the studied traits. The inbred lines L2, L4 and L6 showed the best desirable GCA effects for earliness, L6, L7 and L10 for shortness and L4, L5, L6, L7 and L9 for lower ear placement. Whereas the inbreeds L3, L6 and L7 were the best general combiners for grain yield. The crosses L2×T1, L8×T1, L1×T2, L7×T2, L3×T3, L6×T3 and L10×T3 had the best SCA effects for grain yield. The ten inbred lines were classified into three different heterotic groups using HSGCA method. These groups could be used for selecting the best parents for making crosses in maize breeding programs.

Molecular Genetic Diversity and Line × Tester Analysis for Resistance to Late Wilt Disease and Grain Yield in Maize

Late wilt disease (LWD) caused by the fungus Magnaporthiopsis maydis poses a major threat to maize production. Developing high-yielding and resistant hybrids is vital to cope with this destructive disease. The present study aimed at assessing general (GCA) and specific (SCA) combining abilities for agronomic traits and resistance to LWD, identifying high-yielding hybrids with high resistance to LWD, determining the parental genetic distance (GD) using SSR markers and investigating its relationship with hybrid performance and SCA effects. Ten diverse yellow maize inbred lines assembled from different origins and three high-yielding testers were crossed using line × tester mating design. The obtained 30 test-crosses plus the check hybrid TWC-368 were evaluated in two field trials. Earliness and agronomic traits were evaluated in two different locations. While resistance to LWD was tested under two nitrogen levels (low and high levels) in a disease nursery that was artificially infected by the pathogen Magnaporthiopsis maydis. Highly significant differences were detected among the evaluated lines, testers, and their corresponding hybrids for most measured traits. The non-additive gene action had more important role than the additive one in controlling the inheritance of earliness, grain yield, and resistance to LWD. The inbred lines L4 and L5 were identified as an excellent source of favorable alleles for high yielding and resistance to LWD. Four hybrids L5 × T1, L9 × T1, L4 × T2, and L5 × T2, exhibited earliness, high grain yield, and high resistance to LWD. Parental GD ranged from 0.60 to 0.97, with an average of 0.81. The dendrogram grouped the parental genotypes into three main clusters, which could help in reducing number of generated crosses that will be evaluated in field trials. SCA displayed significant association with the hybrid performance for grain yield and resistance to LWD, which suggests SCA is a good predictor for grain yield and resistance to LWD.

Genetic analysis of semolina recovery and associated traits- A step towards breeding for specific end uses in sorghum (Sorghum bicolor (L.) Moench

High yielding sorghum cultivars with desired specific end-use quality are required to meet the industrial demand. Breeding genotypes for specific end-use helps in increasing profitability to the farmers. This study was conducted to determine the genetic mechanisms underlying the semolina recovery and associated grain traits in sorghum, and to understand the combining ability effects of selected lines for desirable grain quality and yield. Eight lines and eight testers were intercrossed in line x tester mating design, and the resulting hybrids and the parents were evaluated over two years in RCBD replicated thrice. Significant (P < 0.01) genotype, year and genotype × year interaction effects were observed for all the traits, indicating good genetic variability. Correlation analysis indicate that semolina recovery had significant positive associations with endosperm texture (r = 0.53) and grain hardness (r = 0.43) suggesting that genotypes with corneous endosperm yield high semolina. There is a possibility of improving both yield and semolina recovery since they are independent of each other. General combining ability and specific combining ability effects were significant for semolina recovery and most other traits indicating both additive and non-additive gene action underlying the inheritance of these traits. Biparental mating which can exploit additive and nonadditive gene actions will help in combining the desirable yield and quality in sorghum. Some parents viz, 1111B (L7) and 3183B (L2) among lines and NR3 (T3) among testers had significant GCA effects for both yield and semolina recovery. The line 463B (L8) and the tester NR6 (T6) was good for semolina and the grain traits associated with semolina recovery. Top two hybrids for semolina recovery were 27B (L5) × NR3 (T3) and 1111B (L7) × NR3 (T3). The information generated and the genotypes identified will help the breeders to develop identity specific sorghum genotypes.

Genetic control and assessment of breeding value of selected exotic and local genotypes of taro (Colocasia esculenta) for yield and yield components

The study sought to assess combining ability and establish the gene action involved in the inheritance and heritability of yield and yield components in taro. Five (5) parents and twenty (20) F1 hybrids generated from hybridization were evaluated in 3 locations in Ghana. The field trials were laid in RCBD with three replications. Data measured included number of stolons, number of suckers, corm length (mm), corm width (mm), corm weight (g), yield (kg/ha) and dry matter content. Analysis of variance (ANOVA) was conducted using Statistical Tool for Agricultural Research version 2.0.1. Griffing Method II, Model 1 diallel analysis was used to estimate the general and specific combining ability. Heterosis was estimated for all the F1 hybrids. Heritability and correlation among the traits was also estimated. The ANOVA revealed significant differences among the genotypes for yield and its components. The high magnitude of SCA over GCA, high broad sense heritability over narrow sense heritability and below unity Bakers ratio observed for most of the yield traits studied indicates the predominance of non-additive gene action in the expression of the traits. The highly significant positive heterosis and above parental means recorded for the progenies indicates that effective progress can be made in the development of high yielding varieties of taro. CE/IND/16 which recorded significant positive GCA for all the traits except for number of stolons can be included in hybridization programs for varietal development in taro. Hybrids: CE/MAL/32 $$\times $$ KAO19, KAO19 $$\times $$ CE/IND/16, CE/IND/16 $$\times $$ KAO19 and CE/IND/16 $$\times $$ BL/SM/10 which had high hybrid vigor across the research environments could be further evaluated in other environments to ascertain their potentials for release to farmers for cultivation. Significant positive association observed between corm weight and yield/ha(kg) and corm width (mm), indicates that breeding for high corm weight and corm width will definitely improve the yield of taro.

GENE ACTION AND COMBINING ABILITY STUDY IN SESAME

The study of gene action and combining ability have been conducted in 28 F1 cross combinations along with eight parents in 8x8 half-diallel scheme following Griffing’s Approach for 14 morphoeconomic traits including seed yield and oil content in sesame. The general combining ability (GCA) and specific combining ability (SCA) component of variation were significant for parents and crosses respectively for all characters except internode length for GCA indicating role of both additive and nonadditive gene action. However, higher proportion of SCA variance (?2 sca) than GCA variance (?2 gca) revealed preponderance of non-additive gene action for all characters except capsule length and capsule width under study. Further, variance due to dominance played a significant role than additive variance in all traits except capsule width and 100-seed weight. Nirmala is considered as the best general combiner owing to its higher estimate of gca effects for yield per plant, for days to maturity, plant height, branches per plant, capsules per plant, seeds per capsule, capsule length and 100-seed weight. Among cross combinations; Rama × GT-10, AT-382 × Krishna, AT-382 × Nirmala, Krishna × Nirmala, Krishna × Uma, Nirmala × Prachi and Prachi × Uma showed significantly higher sca effect for seed yield per plant in the desired direction indicating their merit for recovery of transgressive segregants for higher productivity following reciprocal recurrent selection.

COMBINING ABILITY IN RELATION TO HETEROSIS EFFECTS AND GENETIC DIVERSITY IN COTTON USING LINE X TESTER MATING DESIGN

The aim of this study was to investigate the relationship between specific combining ability, genetic diversity of parents and heterosis over better parent effects. This research, having eighteen F1 crosses derived from crossing between six lines and three testers, was conducted in order to estimate combining ability, to determine the nature of gene action and heterosis for yield and fiber quality traits and to detect the appropriate crosses for cotton breeding program. The experiment was conducted on randomized complete block design with three replications. The analyses of variance showed significant differences among the genotypes, parents (lines and testers) and crosses for all the studied traits. Estimates of both general and specific combining ability effects were significant for most traits, indicating the importance of both additive and non-additive gene effects for these traits. While, specific was higher than general combining ability variances, for all traits, showing non-additive gene action controlling and therefore, heterosis breeding may be rewarding. The heterosis value varied from cross to cross and from trait to trait. This dissimilarity coefficient was ranged from 3.234 between Giza 85 and Giza 80 to 71.002 between Giza 96 and 10229. Association between heterosis over better parent and specific combining ability was positive and significant for all the studied traits except lint yield / plant. No correlations were found between SCA and GD for all the studied traits. Similarly, heterosis effects was negatively significantly correlated with GD only in the case of boll weight, lint yield / plant and uniformity ratio %, while showed positive and significant correlation for fiber strength and micronaire value. Four crosses showed both positive and significant heterosis and specific combining ability for most yield traits. The parents of these crosses belong to different clusters. Crossing diverse parents could produce high heterotic performance in hybri

Generation mean analysis for seed yield and its component traits in five crosses of castor (Ricinus communis L.)

The present study was carried out to estimate gene effect, heterosis, inbreeding depression, heritability and expected genetic advance for seed yield and its component characters in five crosses of castor (Ricinus communis L.). The analysis of variance revealed significant differences among different crosses and among different generations within cross for all the characters studied. In the present study, both additive and non-additive gene actions were found to be important for the expression of seed yield and most of its component traits indicating that intermating among the selected segregants to break the undesirable linkage followed by one or two generations of selfing could facilitate the accumulation of favorable alleles for the improvement of these traits. However, some of the characters in various crosses were governed by fixable (additive and additive x additive) gene effects and hence, these characters could be improved through pedigree method of selection. Significant heterosis and heterobeltiosis in desired direction observed for seed yield and its majority of the components viz., number of total and effective branches/plant, number of capsules on primary raceme, shelling out turn and 100-seed weight suggested the possibility of utilizing hybrid vigour on commercial scale. High estimates of broad as well as narrow sense heritability along with high genetic advance observed for seed yield/plant in cross I (SKI 324 x PCS 124), cross II (ANDCI 10-7 x JH 109) and cross V (ANDCI 10-7 x SKI 324) suggested the preponderance of additive/fixable gene effect and hence this character could be further improved by adopting selections in succeeding segregating generations. The combination of low narrow sense heritability along with low genetic advance detected for few characters indicated the major role of non-additive gene action and therefore, heterosis breeding or population improvement approach would be more effective for the improvement of these traits. It is being suggested that the parental genotypes SKI 324, ANDCI 10-7 and ANDCI 8 due to their presence in high heterotic combinations viz., ANDCI 10-7 x JH 109 and ANDCI 8 x SKI 324 need to be further exploited in future castor breeding programme.

Genetic variability, heritability and genetic advance studies for economically important traits in sunflower (Helianthus annuus L.)

The present investigation was carried out to study genetic parameters for eight different traits viz., days to 50 per cent flowering, days to maturity, plant height, head diameter, 100 seed weight, volume weight, seed yield/plot and oil content at ICAR-Indian Institute of Oilseeds Research during rabi 2019-2020. The study included a total of 67 genotypes including 5 CMS lines and 10 newly developed restorer lines and their 50 F1 hybrids along with two checks (KBSH-44 and DRSH-1). Analysis of variance revealed significant differences for all the traits. High variation was observed for plant height and seed yield/plant and lowest was observed for 100 seed weight, oil content and head diameter. The difference between GCV and PCV was low for all the characters indicating less influence of environmental factors on the expression of these traits. High heritability with high genetic advance was observed for plant height, head diameter, 100 seed weight and seed yield/plant indicating additive gene action in the expression of these traits. Simple phenotypic selection may be effective for improving these characters. High heritability coupled with low genetic advance was observed for oil content suggesting involvement of non-additive gene action in the expression of this trait indicating little scope for further improvement through individual plant selection.

Gene Action Studies in Cowpea Inbreds and Hybrids with Varying Levels of Heterosis

Background: Cowpea is an important pulse crop grown worldwide that fits well in a variety of cropping systems. Improvement in yield and related characters along with reduced duration are desirable traits in this crop. The study of heterosis reveals the type of gene action involved which enables the plant breeder to adopt suitable breeding methodology for its improvement. Methods: The present investigation was carried out with 10 parent partial diallel design to analyse the gene action and estimate of heterosis with respect to nine yield related traits in cowpea.Result: Highly significant variances observed for all the traits indicated that hybrids and parents were different from each other for the traits under study and that variability in the breeding materials was attributed to additive and non-additive gene effects. Perusal of the data revealed significant positive heterosis for all yield related traits and significant negative heterosis for days to 50% flowering indicating earliness. Among the twenty five crosses studied, VS9 x VS43, VS24 x VS45 and VS44 x VS47 had significant heterosis for maximum number of characters. Both gca and sca variances were significant for all the characters indicating both additive and non-additive gene actions controlling the various traits. The additive variance was much higher than dominance variance for the characters days to 50% flowering, pod length, pod breadth, pod weight, pods per plant and cluster, pod yield per plant, seeds per plant and length of harvest period suggesting the preponderance of additive gene action.

Combining Ability and Gene Action for Yield Characteristics in Novel Aromatic Cytoplasmic Male Sterile Hybrid Rice under Water-Stress Conditions

Hybrid rice parental lines with better combining abilities provide an efficient tool to increase rice production. In the current study, twenty hybrid combinations were generated from five aromatic cytoplasmic male sterile (CMS) lines and four restorer lines (three of them aromatic) using a line × tester mating design. The hybrids and their parental lines were evaluated under two water regimes: normal irrigation and water-stress. Ten yield-component traits were studied over a period of 2 years, and the significant differences between the parents and hybrids are reported in this investigation. Overall, all yield component traits were significantly affected by the water deficit and were governed by both additive and non-additive gene actions. More specifically, the grain yield (GY) was mainly controlled by non-additive gene action under both normal and water-stress conditions. The contribution of the additive variance (σ2 A) was more prominent in the genetic components of traits as compared to the dominance variance (σ2 D). The aromatic parental line CMS IR58025A and the restorer line PR2 were recorded as the best combiners for the GY and good combiners for many other characteristics under both growth conditions. The cross combinations Pusa12A/IR25571-31R and Pusa12A/Giza-Basmati-201 revealed significantly positive specific combining ability (SCA) effects for the GY under both normal and water-stress conditions. The inconsistent correlation between the general combining ability (GCA) and SCA manifested complex interactions among the positive and negative alleles of the genes controlling the yield traits. Generally, the findings of this investigation demonstrated the importance of the GCA and SCA for understanding the genetic components and gene actions of the yield characteristics in new aromatic hybrid rice parental lines. Therefore, we recommend considering these findings in the selection of elite parents for developing superior aromatic hybrid rice varieties under water-stress conditions.

Effects of Heat Stress on Growth, Physiology of Plants, Yield and Grain Quality of Different Spring Wheat (Triticum aestivum L.) Genotypes

Heat stress is one of the major threats to wheat production in many wheat-growing areas of the world as it causes severe yield loss at the reproductive stage. In the current study, 28 crosses were developed using 11 parental lines, including 7 female lines and 4 male testers following line × tester matting design in 2018–2019. Twenty-eight crosses along with their 11 parental lines were sown in a randomized complete block design in triplicate under optimal and heat stress conditions. Fifteen different morpho-physiological and grain quality parameters were recorded at different growth stages. Analysis of variance illustrated the presence of highly significant differences among wheat genotypes for all traits under both optimal and heat stress conditions. The results of combining ability unveiled the predominant role of non-additive gene action in the inheritance of almost all the studied traits under both conditions. Among parents, 3 parental lines WL-27, WT-39, and WL-57 showed good combining ability under both normal and heat stress conditions. Among crosses, WL-8 × WT-17, WL-37 × WT-17, WL-7 × WT-39, and WL-37 × WT-39 portrayed the highest specific combining ability effects for grain yield and its related traits under optimal as well as heat stress conditions. Biplot and cluster analysis confirmed the results of general and specific combining ability by showing that these wheat crosses belonged to a highly productive and heat tolerant cluster. Correlation analysis revealed a significantly positive correlation of grain yield with net photosynthetic rate, thousand-grain rate, and the number of grains per spike. The designated parental lines and their crosses were selected for future breeding programs in the development of heat resilient, climate-smart wheat genotypes.

Manifestation of heterosis and combining ability for yield and its attributes in sesame (Sesamum indicum L.) using line x tester mating design

The present investigation was conducted in sesame to estimate heterosis and combining ability for yield and yield attributing traits using line x tester mating design. Four lines and three testers were crossed to produce 12 F1 hybrids. The heterobeltiosis for seed yield per plant ranged from -16.51 to 24.57%, while the standard heterosis ranged from -12.74 to 33.58% over standard check variety DS-5. Analysis of variance for combining ability revealed that the mean squares due to lines x testers interaction showed significant for all characters. The significant variances due to lines, testers and line x tester showed the involvement of both additive and non-additive gene actions in controlling the traits. General and specific combining ability (GCA and SCA) variances showed major contribution of additive gene action for all the nine characters studied except number of seeds per capsule. AT 238 and JCS 2698 exhibited high gca effects and good per se performance for seed yield per plant and should be utilized in multiple crossing programmes. The sca effect of the crosses indicated that five hybrids manifested significant and positive sca effects for seed yield per plant. Among these, the best three specific combiners were AT 238 x DSS-9, AT 238 x DS-5 and TKG 506 x DSS-9.

Genetic dissection of physiological traits over trait based breeding in bread wheat conferring terminal heat tolerance

Breeding of heat-tolerant cultivars requires knowledge of the genetic behavior of morpho-physiological traits. Gene action was investigated using wide phenotypic segregation ranging across six generations (P1, P2, F1, BC1, BC2 and F2) of four different tolerant × sensitive crosses for grain filling duration, GFD (40.14–46.20); canopy temperature depression, CTD (2.42–5.97); normalized difference vegetation index, NDVI (0.35–0.61); membrane thermostability index, MSI (31.40–40.93); no. of grains/spike, GN/SP (26.29–54.80); thousand-grain weight, TGW (31.70–44.45); and grain yield/plant, GY (15.37–24.89) under terminal heat stress. Scaling results indicated an absence of epistasis for MSI and TGW in cross PBN51 × HUW510. The prominence of Dominance × dominance interaction over additive × additive and additive × dominance interactions along with significant dominant gene effect [h] for all traits except MSI was observed. For MSI, similar signs of [d] and [i] along with significant [j] showed the possibility of exploitation of additive gene effect. CTD, NDVI and GN/SP were controlled by duplicated epistasis, whereas both complementary and duplicate epistasis was found for GFD. Digenic interactions with prominent duplicate epistasis indicate that biparental mating or diallel selective mating might be efficiently utilized for their improvement. The present investigation indicated a preponderance of non-additive gene action for studied traits, thus, implying toward delaying of selection to the later generations to exploit transgressive segregants. Any conventional breeding strategy would be followed for generating the cultivars with low CTD, reduced cell membrane injury, with higher NDVI, TGW, GFD, no. of grains/spike and grain yield/plant.

Combining Ability Studies for Forage Yield and Its Components in a Diallel Cross of Pearl Millet

Combining ability and interrelationships information was derived on eight agronomic traits including the time to 50% flowering, plant height, tiller no. /plant, fresh weight of plant, stem thickness, green forage yield, leaf area/plant and leaf area index, from a diallel cross involving five diverse pearl millet ( Pennisetum glaucum ) parents, developed in ICRISAT. The parents along with their crosses (excluding reciprocals) were grown in a complete block design with three replications at the University of Gezira Farm, July 1999. The objectives of this study were to measure and evaluate combining ability for forage yield and to explore the possibility of developing high forage yielding open-pollinated varieties and/or hybrids. Significant variability among entries was observed for all the traits measured except time to 50% flowering. The entries were also significantly different for all characters concerning their means ranking. The present study indicated predominantly non-additive gene action for most of the studied traits. However, considerable additive gene action was also indicated for the characters' plant height, fresh weight of plant and leaf area/plant. It was observed that good general combiners for forage yield were AlPop 88, AfPop 90 and Sudan yellow parents. Concerning the incorporation of desirable characteristics, recurrent selection can be efficiently used for making improvements in yield. The best crosses for forage yield were AfPop 90 X Sudan yellow (38.75 t/ha) and AfPop 88 X AfPop 90 (44.48 t/ha). Keywords: Combining ability, Forage, Pennisetum glaucum, a diallel cross DOI: 10.7176/JBAH/11-6-04 Publication date: March 31 st 2021

Heterosis and inbreeding studies for seed cotton yield and its component traits in desi cotton

A study was conducted to assess the extent of the heterosis for sixteen yield and yield-attributing traits in four cotton hybrids (each having P1, P2, F1, F2, BC1 and BC2 generations) obtained by crossing four interspecific lines of desi cotton in a compact family block design with three replications during kharif 2017-18. Highly significant and positive relative heterosis, heterobeltiosis and inbreeding depression were recorded in most of the crosses. For seed cotton yield per plant, positive and highly significant relative heterosis, heterobeltiosis and inbreeding depression were recorded in all the four crosses indicated major role of non-additive gene actions in the inheritance of seed cotton yield per plant and its attributes, while cross III (GShv 362/12 x PA 812) recorded the highest heterotic effect among all crosses which also performed well for monopodia per plant, average boll weight, lint yield per plant, ginning percentage, lint index, fibre fineness and fibre strength.

ASSESSING THE COMBINING ABILITY OF RICE GENOTYPES IN F1 GENERATION USING COMPLETE DIALLEL CROSS

A complete diallel analysis was carried out to determine combining ability of Shandar, NIA-Mehran, NIA-19/A, KS-282 and Shua-92 rice varieties in F1 during 2017. The objective of the study was to identify potential recombinants for future rice breeding program. The research was conducted at Nuclear Institute of Agriculture, Tandojam. Genotypic mean squares were significant (P ?0.01) for all of the traits i.e.; days to heading, days to maturity, plant height, number of tillers plant-1, panicle length, grains panicle-1 and grain yield plant-1 indicating genetic variation. Importance of both additive and non-additive gene action was found with preponderance of additive genetic effects in expression of traits studied. Showing negative GCA effects, NIA-Mehran, NIA-19/A and Shua-92 proved better parent varieties for developing early maturity. While, NIA-Mehran, KS-282 and Shua-92 for developing short stature genotypes. While, Shandar remained the best combiner for yield and yield associated traits with higher positive GCA effects. Cross combination of Shandar × KS-282 was the best with higher negative effects for days to heading and maturity and higher positive effects for grain yield plant-1. NIA-Mehran × Shua-92 gave the highest negative SCA effects indicating best combination for short stature. In case of number of tillers plant-1 and grains panicle-1, the cross NIA-19/A × KS-282 was the better combination with the highest positive SCA effects. Shandar × NIA-Mehran manifested the highest value for panicle length. Findings of reciprocal SCA revealed that the reciprocal cross combination of Shua-92 × Shandar was fruitful illustrating negative effects for days to heading and maturity. While, KS-282 × NIA-Mehran was the best reciprocal combination for yield and yield associated traits. It is concluded that rice varieties Shandar and NIA-Mehran could be used to improve yield contributing traits in rice, while, NIA-Mehran and KS-282 may be used to improve early maturity and short stature in rice crop.

Genetic Component and Vr-Wr Graphical Analysis in Blackgram [Vigna mungo (L.) Hepper

Background: To develop a new high yielding variety, it is important to generate utilitarian recombinants and devise an appropriate strategy for selection and advancement of those recombinants. Method: Keeping this in mind, genetic components of yield and its related traits were determined in nine genotypes of blackgram through half diallel analysis using Hayman’s numerical and graphical approach. Conclusion: The estimates of genetic components deduced the role of non-additive gene action in the inheritance of all traits. The Vr-Wr graphical analysis revealed that assumptions laid by Hayman for diallel analysis were seldom fulfilled. Epistatic effect was predominant in all traits except days to 75 per cent maturity. Unidirectional dominance was observed in days to 75 per cent maturity, pods per plants and seed yield per plant and crude protein content. One major gene group was found controlling all traits except days to 75 per cent maturity and branches per plant. These findings can be used by breeders to devise appropriate selection methodology for yield improvement in blackgram.

Inheritance and combining ability estimates for cowpea resistance to bruchid (Callosobruchus maculatus Fab.) in Benin cowpea

Cowpea bruchid (Callosobruchus maculatus Fab.) is the most important storage pest causing significant economic losses. Development of bruchid resistant cowpea varieties is the most sustainable strategy for controlling bruchid. However, information regarding the nature of gene action governing the resistance to bruchid is limited for cowpea genotypes in Benin. This study aimed to understand the genetic basis of cowpea resistance to C. maculatus. Eight parents were crossed in a full diallel mating design. 56 F2 progenies were tested with the eight parental genotypes in alpha lattice design with three replications in laboratory. Data were recorded on bruchid emergence (BE); weight loss (WL); median development period (MDP); Dobie susceptibility index (DSI); number of eggs laid (NEL); average number of holes (ANH); seed damage (SD). Combining ability analysis was performed using Griffin's method 1, model 1 in AGD-R software. The results showed that general combining ability (GCA) effects were highly significant (p < 0.001) and negative for BE, WL, DSI, NEL, ANH, and SD on the parents. Significant positive GCA effects were observed for MDP. Thus, the parents TVU13677, IT84S2246-4, WC36 and WC66*5T were the best combiners for bruchid resistant. High narrow sense heritability was observed for BE (0.75), WL (0.69), DSI (0.72), ANH (0.77) and SD (0.69). These results showed that both additive and non-additive gene action govern the resistance to bruchid in cowpea. The genotypes (TVU13677; IT84S2246-4; WC36; WC66*5T) and the resistant crosses were the promising genotypes and can be used in breeding programs seeking to develop bruchid resistant cowpea varieties. • Cowpea is a major source of dietary protein in Sub-Saharan Africa. • Bruchid is the most important storage cowpea pest causing significant losses. • This study evaluated the Inheritance of C. maculatus resistance in cowpea. • The hopeful cowpea genotypes useable in breeding programs were found.

Combining ability, gene action and heterosis analyses of maize lines that were developed for maize streak virus resistance and acidic soil tolerance

Aluminium toxicity in acidic soils (Al) and the maize streak virus disease (MSV) cause significant losses in maize productivity. These constraints can occur simultaneously in sub-Saharan Africa but there are no maize hybrids that combine resistance for both stresses. Therefore, the objectives of the study were to determine combining ability, gene action and heterosis for MSV and Al tolerance in maize. Ninety-nine experimental hybrids were generated from a 10 × 10 factorial mating design. The experimental maize hybrids, and 21 commercial hybrids were evaluated for MSV resistance under artificial infestation in Zimbabwe, and for grain yield and agronomic performance across eight environments in South Africa and Zimbabwe. Ninety-seven experimental hybrids and five standard control hybrids were evaluated for Al tolerance in a laboratory in South Africa. There were significant (p < 0.05) differences among hybrids for agronomic traits, grain yield, and MSV and Al toxicity tolerance. Only general combining ability effects were significant (p < 0.05) for grain yield and grain moisture content, while specific combining ability effects were significant (p < 0.05) for number of ears and ear prolificacy. Both GCA and SCA effects were significant for the Al toxicity tolerance related traits, indicating that Al tolerance was governed by both additive and non-additive gene action. Although hybrids displayed highly significant variation for MSV resistance, the GCA and SCA mean squares were not significant and only accounted for 59% of the hybrid sum of squares, suggesting that MSV resistance was partly under qualitative inheritance. The F1 hybrids displayed MSV severity scores similar to those of their MSV resistant parents, suggesting that probably simple dominance gene effects were involved. The hybrids also displayed significantly high levels of heterosis for both Al and MSV resistance, indicating that hybridisation would be effective in generating improved varieties. At least 60% of the hybrids were resistant to Al toxicity and more than 87% were MSV resistant, indicating that there is potential to develop varieties with resistance to both stresses.