General Combining Ability Effects Research Articles

EFECTOS GENÉTICOS SOBRE LA EXPRESIÓN DE LA CALIDAD DE LA SEMILLA DEL PIMIENTO GUAJILLO

<p><strong>Background. </strong>Even though many studies have been done in agronomic characters, there is no knowledge about studies that address the genetic effects on the physical and physiological quality of seeds in native populations of Guajillo chile (<em>Capsicum annuum</em> L.). <strong>Objective.</strong> The objective of this research was to identify the effects of general combining ability (GCA), and specific (SCA) on seed quality variables, as well as to determine the type of gene action in them. <strong>Methodology.</strong> F<sub>1</sub> and F2 seeds were analyzed from native populations of chili Guajillo through the accelerated aging test and digitization of seed images. <strong>Results. </strong>The results obtained show that: 1) all the variables were significant for the GCA and SCA, which indicates that the additive and non-additive effects are involved in the genetic control of these characters; 2) In the crosses with the highest average, at least one progenitor with a high GCA effect participated; 3) The effects of GCA were more important than the effects of SCA for the physical quality of seed, length and fresh seedling biomass; 4) In general, heritability in the narrow sense varied from low to moderate (0.00-0.30). <strong>Implications.</strong> The information generated about the non-additive genetic effect on the quality of Guajillo seed, can be used in breeding programs applying the hybridization technique. <strong>Conclusions. </strong>There is no relationship between the best crosses and parents with the effects of GCA high. The parents used in this research have acceptable GCA for most traits, crosses with higher SCA values do not necessarily derive from parents with acceptable GCA values.</p>

Genetic analysis of grain yield and resistance of extra‐early‐maturing maize inbreds to northern corn leaf blight

AbstractMaize (Zea mays L.) is a food security crop in sub‐Saharan Africa (SSA). Incidence of northern corn leaf blight (NCLB), caused by Exserohilum turcicum, in lowlands of SSA during the past decade has caused 30–70% reduction in maize yield. This study (a) examined the combining abilities of extra‐early maize (EEM) inbreds and classified them into heterotic groups; (b) elucidated gene action controlling resistance to NCLB; (c) assessed grain yield (GYLD) and yield stability of EEM hybrids under NCLB infection; and (d) identified testers. One hundred and fifty EEM hybrids, obtained by crossing 15 inbreds each of white‐ and yellow‐endosperm maize using the North Carolina Design II, plus six checks, were evaluated in nine environments, six of which were inoculated with an isolate of E. turcicum and three of which were non‐inoculated in 2018 and 2019. The white and yellow inbreds were placed in three heterotic groups using the heterotic grouping based on general combining ability (GCA) of multiple traits and stability of GYLD using the genotype plus genotype × environment (GGE) biplot analysis. The GCA, specific combining ability (SCA) and genotype × environment (G×E) interactions were significant for GYLD, disease severity, and other measured traits. The GCA effects were more important than the SCA effects for GYLD and NCLB severity scores across environments, implying that recurrent selection could facilitate improvement for GYLD and NCLB resistance. Three inbred testers and four single‐cross testers were identified for developing high‐yielding NCLB‐resistant hybrids. Four white and five yellow single‐cross hybrids were identified for on‐farm testing and possible commercialization.

Resolvable mating-environmental designs for partial triallel cross experiments

Triallel crosses can be readily exploited as breeding tool for developing commercial hybrids with traits of genetical and commercial importance by acquiring information on specific combining ability effects along with general combining ability effects if the experimentation size is reduced to an economical extent. In this paper, methods of constructing designs involving partial triallel crosses in smaller blocks using different types of lattice designs have been introduced. The designs have low degree of fractionation, which suggests their utility when there is a resource crunch. Canonical efficiency factor of these designs relative to an orthogonal design with same number of lines, assuming constant error variance for both situations, is high indicating that adoption of these designs for the trials could bring about improvement as the recommendations from the experiment will be associated with a high precision.

Combining ability of bread wheat genotypes for yield and yield-related traits under drought-stressed and non-stressed conditions

Drought is a major cause of reduced yields in dryland wheat production. This study aimed to determine the combining ability effects of selected bread wheat genotypes (Triticum aestivum L.) for yield and yield-related traits. Eight parental lines were selected and crossed using a half-diallel mating design. The parents and 28 crosses were evaluated at two sites in Ethiopia, representing drought-stressed and non-stressed conditions, using a 6 x 6 simple lattice design. The parental line ETW17302 was the best general combiner for the growth indices: days to heading, days to maturity, grain-filling period, and 1 000-kernel weight, thereby enabling direct selection for improved grain yield under a drought-stressed condition. Parent ETW17377 could also be used for improving grain yield under a drought-stress condition owing to its positive and significant general combining ability effect on grain yield. The families ETW17302 × ETW17377, ETW17396 × ETW17374, and ETW17396 × ETW17385 were the best specific combiners for improving grain yield under the drought-stressed condition. The selected parents and families are desirable genetic resources to enhance yield and yield-related traits under both drought-stressed and non-stressed conditions.

Combining ability studies in the advanced lines of bottle gourd [Lagenaria siceraria (mol.) Standl.] for growth, earliness and yield parameters

The present investigation was carried out with the objective to study the combining ability of parents and hybrids for growth, earliness and yield parameters in bottle gourd. General combining ability effects of parents and sca effects of crosses were highly significant for the characters studied. The parents Bot.G-4, Bot.G-7 and Kolkata Collection are the good general combiners for fruit yield per vine. The line Bot.G-6-2 exhibited significant and maximum gca effects for vine length and number of branches. The line Kolkata Collection showed maximum and significant gca effects for days to first female flower, days to first harvest and sex ratio. Tester Samrat exhibited significant gca effects for vine length, number of branches, nodes up to first female flower, sex ratio and fruit yield per vine. Among crosses, the cross Bot.G-6-2 X Arka Bahar exhibited significant sca effects for vine length and fruit yield per vine. While the cross Bot.G-6-1 X Samrat showed significant sca effects for days to first female flowering and days to first harvest. The cross Bot.G-6 X Samrat exhibited maximum and significant sca effects for nodes up to first female flowering and sex ratio. It is evident that gca or sca effects in parents or hybrids were in desirable for some other traits. Therefore it is important to ascertain the status of parent or hybrid with respective to combining ability effects over a number of component characters.

Combining ability of soybean (Glycine max L.) yield performance and related traits under water-limited stress conditions

Development of improved genotypes requires acquiring adequate information on genetic background and nature of gene action for planning appropriate breeding and selection strategies. This study was aimed at obtaining estimates of general and specific combining ability, identifying the best combiners in developing drought tolerant genotypes and determining gene action of soybean traits. Six genotypes were crossed using the North Carolina II mating design to form eight families, of which Makwacha and Nasoko were regarded as males and TGX1990-137F, TGX1987-23F, 1988-70F and Tikolore were regarded as females. Two-hundred F2 progeny and six parents were evaluated in the field under non-water-limited stress (non-WLS) and water-limited stress (WLS) conditions across 2 sites during the 2018 dry season in a split-plot layout. Water-regimes were allocated to main plots and genotypes to subplots in a randomized complete block design with 3 replications. Significant genotype and water regime effects were found for seed yield and yield components. Most progeny ranked higher than parents under WLS conditions for all traits. Significant general combining ability (GCA) and specific combining ability (SCA) effects for all traits indicated that both additive and non-additive gene effects were important for trait expression under WLS conditions. Both GCA and SCA effects significantly interacted with water regime effects, demonstrating the need for testing of potential progeny across varied WLS levels to determine stable genotypes. Parents and F2 progeny with significant positive GCA and SCA effects, respectively, under WLS were identified as potential material for inclusion in the breeding program for drought tolerance.

Genetics of dual resistance to african stem borer, busseola fusca and spotted stem borer, Chilo partellus in sorghum

African stem borer, Busseola fusca Fuller (Noctuidae) and spotted stem borer, Chilo partellus Swinhoe (Crambidae) cause more than 40 % of grain yield loss in cereals and bothpests co-exist in mid-altitudes in Kenya. Development of sorghum with dual resistance to B. fusca and C. partellus has been difficult due to the inadequate understanding of inheritance of resistance traits to the two species. The objective of this study was to investigate the genetics of dual resistance to the two insect species in sorghum. Thirty sorghum populations derived from crossing sorghum lines with varying levels of resistance to the two insect species were studied. The experiments were conducted in two separate sites at Embu and Kiboko in Kenya with two replications per site. North Calorina Design II mating design was used. Artificial infestation with first instar neonates of each pest species was done at 30 days after planting in both sites. Data collected included sorghum damage due to the two borer species and agro-morphological traits. Genetic analyses were performed using line x tester method using Genstat statistical software. Data analyses revealed that general combining ability (GCA) and specific combining ability (SCA) effects were significant for foliar and stem damage traits, indicating that additive and non-additive gene effects conditioned resistance to B. fusca and C. partellus. Sorghum lines ICSA 464, ICSB 474, ICSB 464 and ICSA 472 and ICSB 473 exhibited desirable high negative GCA effects to B. fusca and C. partellus. These parents could be used in development of sorghum with dual resistance to B. fusca and C. partellus thus contributing to sustainable integrated management of these two stem borer species in sorghum via host plant resistance management.

Combining Ability of White Maize Inbred Lines Via Line X Tester Analysis

Combining ability analysis was conducted using line x tester design for seven inbred lines of maize which were crossed to three single crosses as testers at Ismailia Agricultural Research Station during 2016 growing season. In 2017 season, 21 crosses in addition to one check hybrid were evaluated at three locations. Highly significant differences were found between the locations for all studied traits. Mean squares due to crosses, their partitions and their interaction with locations were significant or highly significant for all studied traits, except for lines and lines x testers for number of ears/plant and testers for number of rows/ear. The best inbred lines for general combining ability effects were Gz-8093, Gz-8092 and Gz7253 for earliness and Tep-6240 for grain yield. the tester SC 131 was the best general combiner for days to 50% silking toward earliness, grain yield, number of ears/plant, ear length and ear diameter. The cross Gz-8093 x SC131 had the desirable SCA effects for all traits also. The additive gene effects were more important than the non-additive gene effects in inheritance of days to 50% silking, number of ears/plant, ear length and ear diameter while, the non-additive was more important than additive for grain yield, number of rows/ear and number of kernels/row. The non-additive gene effects were more affected by environment than additive gene effects for all traits except for number of ears/plant. The cross Gz-8093 x SC131 highly significantly outyielded to the TWC 324, suggesting the use of this cross in maize breeding programs.

Effect of genotype, sex and parity on growth traits of diallel crossed Nigerian indigenous and exotic pigs

Three breeds of pig namely; Indigenous (IN), Large white (LW) and Landrace (LR) breeds were crossed in full diallel arrangement to evaluate the effects of cross, sex and parity on growth traits as well as establish the nature of gene action due to the growth traits at birth, weaning and 20 weeks of age. Each line crossed in a full 3x3 diallel cross resulted in a total of 132, 107 and 105 pigs at birth, weaning and 20 weeks of age respectively. General Combining Ability (GCA), Specific Combining Ability (SCA) and Reciprocal Effects (RE) were estimated for eight traits which includes Body weight (BWT), Ear length (EL), Tail length (TL), Heart girth (HG), Snout circumference (SC), Snout length (SL), Height at wither (HW) and Body length (BL). There were significant differences (P < 0.05) among the various crosses, sex and parity but no significant interaction. The LRxLW cross consistently expressed higher body weight and morphometric traits than other crosses at birth, weaning and 20 weeks of age, while the INxIN expressed least body weight at birth and 20 weeks of age, while LWxIN was the least at weaning. There was no significant GCA effect (P>0.05) on all the traits measured, but SCA was significant (P<0.01) for all morphometric traits and body weight. RE was significant for body weight at birth and weaning, while at 20 weeks, was significant for SC and HW. The non-significant GCA estimates along with significant SCA estimates suggest that the genes governing the eight traits measured do not act additively, but non-additively, implying that improvement of those traits may be attained by exploiting heterosis through planned crossbreeding. However, the significant reciprocal effect in body weight and some morphometric traits indicates maternal and sex-linked effect at the affected ages, implying that significant reciprocal cross may be used to attain high performance for the growth traits in the progeny.

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.

Identifying quantitative trait loci for the general combining ability of yield-relevant traits in maize.

Maize is the most important staple crop worldwide. Many of its agronomic traits present with a high level of heterosis. Combining ability was proposed to exploit the rule of heterosis, and general combining ability (GCA) is a crucial measure of parental performance. In this study, a recombinant inbred line population was used to construct testcross populations by crossing with four testers based on North Carolina design II. Six yield-relevant traits were investigated as phenotypic data. GCA effects were estimated for three scenarios based on the heterotic group and the number of tester lines. These estimates were then used to identify quantitative trait loci (QTL) and dissect genetic basis of GCA. A higher heritability of GCA was obtained for each trait. Thus, testing in early generation of breeding may effectively select candidate lines with relatively superior GCA performance. The GCA QTL detected in each scenario was slightly different according to the linkage mapping. Most of the GCA-relevant loci were simultaneously detected in all three datasets. Therefore, the genetic basis of GCA was nearly constant although discrepant inbred lines were appointed as testers. In addition, favorable alleles corresponding to GCA could be pyramided via marker-assisted selection and made available for maize hybrid breeding.

Genetic consequence through combining abilities for yield and its components traits of Brassica species

The estimates of general combining ability effects suggested that among females GDM-4 and among males IC-399819 and EC-766060 were the best general combiners for seed yield and few other characters. The estimates of specific combining ability revealed that the hybrids GM-2 x EC-766437 followed by GM-2 x RH-406 and GDM-4 x EC-766378 exhibited positive sca effects in desirable direction for seed yield per plant. The hybrid GDM-4 x EC-766043 followed by GDM-4 x RH-749 and GDM-4 x EC-766495 exhibited significant negative sca effects for days to 50 per cent flowering and GM-3 x EC-766437 for days to maturity. While the hybrid GDM-4 x EC-766043 depicted significant sca effects in desired direction for oil and protein content. In general, involvement of both additive and non-additive gene effects, observed for most of the characters suggested that it would be desirable to follow cyclic method of breeding such as reciprocal recurrent selection, which would be most effective to stabilize additive genes to improve population mean and also to generate as well as to retain variability for several cycles of selection.

Detection of Non-Additive Gene Action within Elite Maize Populations Evaluated in Contrasting Environments under Rainforest Ecology in Nigeria

Proper understanding of the mode of gene action in open-pollinated varieties (OPVs) maize parents helps breeder in the choice of appropriate breeding method to improve its genetic value. The objectives of the present study were to determine gene action controlling grain yield and other agronomic traits of late maturing elite OPVs and classify the varieties into heterotic groups. Ninety-one hybrids generated from 14 elite OPV parents using diallel mating design were evaluated with their parents plus three commercial checks under marginal rainfall, drought, and optimal environments in Nigeria from 2017 to 2018. The experiment was laid out in a 9 × 12 alpha lattice with three replications in each environment. Results showed that there were significant mean squares for grain yield and most agronomic traits. Significant general combining ability (GCA) and specific combining ability (SCA) mean squares for some of the traits indicated that additive and non-additive genetic gene actions were important in the inheritance of yield and those traits among this set of genotypes. However, non-additive genetic effects were more important than additive for grain yield and other agronomic traits in all research environments. Only TZL Comp-3 C3 DT had significant and positive GCA effects (0.336*) while three hybrids had significant and positive SCA for grain yield across research environments. Because of the preponderance of non-additive gene action over additive gene action, distinct heterotic groups could not be identified but four tester groups were identified by HSGCA (Heterotic grouping based on Specific and General Combining Ability) and three groups by HGCAMT (Heterotic grouping based on the GCA of Multiple Traits). Results of grouping were not related to the endosperm colour but grouping based on HGCAMT was related to the pedigree of the varieties. In conclusion, this study has demonstrated preponderance of non-additive gene action over the additive gene action for all measured traits. The presence of the non-additive gene action present in the studied materials can enhance identification of outstanding varietal hybrids and population testers that can serve as base genetic materials for future maize improvement through reciprocal recurrent selection program in SSA.

Combining Ability Analysis in Sweet Corn (Zea Mays Saccharrata L.) Using Line by Tester Design

Aim The purpose of this study was to investigate the different combination of testcrosses for morphological and yield relating traits and to investigate general combining ability of the inbred lines. Materials and Methods This research was conducted at The University of Agriculture Peshawar, Pakistan during 2016. Line x-tester analysis was used to test general combining ability (GCA) effects of 24 S4 lines of sweet corn. Alpha lattice design with two replications and two checks was used during the experiment. Research data were recorded on various flowering, morphological and yield parameters. Results Highly significant variations were recorded among the testcrosses for the studied traits except anthesis silking interval (ASI), 100-kernel weight. Minimum days to tasseling (48-days) and silking (53.5-days) was exhibited by pop-syn-swt (9-4)×synthetic sweet. GCA effect was -2.14 for tasseling and -2.00 for silking. Maximum value (3.5-days) for ASI was recorded for Pop-synswt 1(8-3)×synthetic sweet, while GCA effect for ASI was -0.71. Lowest plant height (129.8 cm) was recorded for pop-syn-swt 1(3-3)×synthetic sweet, while GCA effect for plant height was observed to be -14.79. Maximum cob length (16.6 cm) was revealed by pop-syn-swt 1(12-2)×synthetic sweet. For cob length GCA effect of 1.01 was recorded. Maximum 100 kernel weight (31.3 g) was estimated for pop-syn-swt 1(2-1)×synthetic sweet. GCA effect of 1.85 was recorded for 100-kernel weight. Highest mean (7143.9 kg ha-1) for grain yield was recorded for pop-syn-swt 1(9-4)×synthetic sweet. GCA effect for grain yield was found to be 1370.93. Conclusion Generally a low GCA value, either positive or negative indicates that the mean of a parent does not largely vary from its offsprings. In contrast, high GCA value suggests that parent is either superior or inferior to the general mean and it has high heritability and less environmental effects. Based on the findings in this research, the above mentioned testcrosses can be included in future sweet corn breeding programs where early flowering and yield attributes is desired.

Effect of genotype, sex and parity on growth traits of diallel crossed Nigerian indigenous and exotic pigs

Three breeds of pig namely; Indigenous (IN), Large white (LW) and Landrace (LR) breeds were crossed in full diallel arrangement to evaluate the effects of cross, sex and parity on growth traits as well as establish the nature of gene action due to the growth traits at birth, weaning and 20 weeks of age. Each line crossed in a full 3x3 diallel cross resulted in a total of 132, 107 and 105 pigs at birth, weaning and 20 weeks of age respectively. General Combining Ability (GCA), Specific Combining Ability (SCA) and Reciprocal Effects (RE) were estimated for eight traits which includes Body weight (BWT), Ear length (EL), Tail length (TL), Heart girth (HG), Snout circumference (SC), Snout length (SL), Height at wither (HW) and Body length (BL). There were significant differences (P &lt; 0.05) among the various crosses, sex and parity but no significant interaction. The LRxLW cross consistently expressed higher body weight and morphometric traits than other crosses at birth, weaning and 20 weeks of age, while the INxIN expressed least body weight at birth and 20 weeks of age, while LWxIN was the least at weaning. There was no significant GCA effect (P&gt;0.05) on all the traits measured, but SCA was significant (P&lt;0.01) for all morphometric traits and body weight. RE was significant for body weight at birth and weaning, while at 20 weeks, was significant for SC and HW. The non-significant GCA estimates along with significant SCA estimates suggest that the genes governing the eight traits measured do not act additively, but non-additively, implying that improvement of those traits may be attained by exploiting heterosis through planned crossbreeding. However, the significant reciprocal effect in body weight and some morphometric traits indicates maternal and sex-linked effect at the affected ages, implying that significant reciprocal cross may be used to attain high performance for the growth traits in the progeny.

Parámetros genéticos y aptitud combinatoria de líneas de maíz para grano

La aptitud combinatoria general (ACG) y la específica (ACE) se usan para identificar combinaciones híbridas entre progenitores con rendimiento mayor o menor que el comportamiento promedio esperado de las líneas progenitoras. El objetivo de este estudio fue evaluar la ACG de 7 líneas como hembras (H) y 4 líneas macho (M); así como la ACE de las 28 cruzas realizadas; como hipótesis se planteó, que los cruzamientos entre líneas con características contrastantes producirán híbridos sobresalientes. La obtención de las líneas con un nivel de endogamia de S3, los cruzamientos y evaluación de estos últimos se realizó en el Campo Experimental de la Facultad de Agronomía de la Universidad Autónoma de Nuevo León, México, las cruzas simples se evaluaron en un diseño experimental de bloques completos al azar con tres repeticiones. El análisis genético se realizó con el diseño II de apareamiento de Carolina del Norte de Comstock y Robinson. Los progenitores, que presentaron más altos rendimientos fueron M2 (8.12 t ha-1) y M4 (7.9 t ha-1) considerados como machos y como hembras H3 y H5 (8.13 t ha-1) ambas con mismo rendimiento; sin embargo, los mayores efectos de ACG fueron en M2 (0.19), M1(0.08), H4 (0.14) y H2 (0.13) en rendimiento de grano. Los efectos mayores en ACE se observaron en las cruzas H4xM2 (1.17 t ha-1), H6xM3 (0.84 t ha-1) y H2xM3 (0.58 t ha-1). En los parámetros genéticos para rendimiento de grano, la varianza ambiental superó a la varianza aditiva y de dominancia, la heredabilidad en sentido amplio y estrecho fueron 87.14 y 52.15%, respectivamente.

Line × Tester Analysis for Estimation Combining ability of some New Yellow Maize Inbred Lines for Grain Yield and Downy Mildew Resistance

A line×tester analysis was performed at Sakha Research Station; during summer 2017, using twenty new yellow maize inbred lines and two testers; inbred line Sk-4 and single cross SC180. The resulting 40 F1 crosses in addition to four check hybrids were evaluated in two trails during summer 2018. The first trail; for yield and other traits, was performed at Sakha and Sids Agricultural Research Stations. The second trial; for downy mildew disease resistance, was carried out under two levels of nitrogen fertilization in the disease nursery at Sakha Station. Significantly differences were detected between the two locations for the most studied traits and between the two nitrogen levels for downy mildew resistance. Significant of differences were observed among lines, testers and their interaction for all studied traits, except among testers for downy mildew resistance and line×tester interaction for plant height, ear height and downy mildew resistance. The non-additive gene effects were predominant in the inheritance of grain yield, ear length, ear diameter and downy mildew resistance. For general combining ability effects, the best general combiners were Sk5013/71 for grain yield and downy mildew resistance. While, the best tester was Sk-4 for grain yield and most traits. The desirable hybrids for specific combining ability effects were Sk5002/62×Sk-4, Sk5005/66×Sk-4 and Sk5021/74×SC180 for grain yield and Sk5004/65×SC180 for downy mildew resistance. Single cross Sk5013/71×Sk4, also three-way crosses Sk5010/69×SC180 and Sk5013/71×SC180 were superior for grain yield and high resistance to downy mildew resistance. These crosses could be use in maize breeding program.

Assessment of Combining ability for some Grain Yield and Quality Traits in Rice (Oryza sativa L.) by using Griffing Method and Biplot Analysis

During 2017 growing season, half diallel crosses were made among six genotypes of rice. The obtained 15 F1 and their parents were evaluated during 2018 growing season to analyze the general combining ability (GCA) and specific combining ability (SCA). For all studied characters, the mean squares due to GCA and SCA were highly significant, indicating the importance of the behaviour of both additive and dominance gene in the heredity of these characters. Variances due to GCA were greater than these due to SCA for all studied traits, except milling and grain elongation. Giza 178 and Giza179 possessed highly significant GCA effects for earliness, panicle length, number of filled grains panicle-1, grain yield plant-1 and hulling. IET1444 was good combiner for cooking traits, beside panicle length and number of tillers plant-1. Seven crosses viz., Giza178xIET1444, Sakha 106x Giza 179, Sakha 105x Giza 179, IET1444x WAB880-SG, Giza178xGiza179, Sakha105xSakha106, and Sakha105xGiza178 evidence positive and significant SCA effects for grain yield plant-1. The cross, Sakha 105xGiza179 recorded significant SCA effect in favourable direction for seven traits viz., days to 50%heading, panicle length, number of filled grains/panicles, grain yield plant-1, milling, grain elongation, and amylose content. Sakha105x Sakha106 rice hybrid showed desirable either negative or positive directions and significant SCA effects for days to 50%heading, plant height, grain yield plant-1, gelatinization temperature and grain elongation. Concerning results obtained by biplot analysis, found agreement between two methods of griffing and biplot for analyzing the half-diallel in determining the best parents and hybrids.

Reciprocal differences and combining ability for growth and yield components in cacao (Theobroma cacao L.): a case of recommended cacao varieties in Ghana

The inappropriate use of cacao clones either as female or male parents in seed gardens have been suggested as some of the reasons for the low yields of cacao hybrid varieties grown in West Africa. The concept of reciprocal effects in cacao crosses has not been well studied. To investigate the impact of maternal effect on growth and yield traits, reciprocal differences and combining abilities of recommended cacao parents in Ghana were evaluated. Six clones, comprising four important seed gardens clones used across West Africa and two clones previously used as standards in international breeding projects were crossed in a 6 × 6 complete diallel mating design to produce 30 F1 progenies. These progenies were tested in the field using a random block design with four blocks and elementary plots containing 20 plants. Growth and yield traits including stem cross-sectional area in juvenile stage, jorquette height, bean weight, number of beans per pod and bean yield were monitored over a 6-year period. Mean squares of general combining ability (GCA), specific combining ability (SCA) and reciprocal effects were significant for almost all the traits except jorquette height in SCA. This indicates that additive and non-additive gene effects are important in the inheritance of the traits. The presence of reciprocal differences for all traits suggests the influence of maternal effects in controlling the traits. Manual pollinations for commercial seed production should, therefore, follow established protocol and clones recommended as female and male parents used strictly as recommended. One of the standard clones, AMAZ15/15 had significant positive GCA effect for yield, and consistently produced progenies with high SCA values. It could be added to parental clones currently used in producing cacao varieties in the seed gardens in Ghana and other West African cacao growing countries.