High Specific Combining Ability Research Articles

Identification of heterosis and combining ability in the hybrids of male sterile and restorer sorghum [Sorghum bicolor (L.) Moench] lines.

In sorghum [Sorghum bicolor (L.) Moench], combining ability and heterosis analysis are commonly used to evaluate superior parental lines and to screen for strongly heterotic hybrids, which helps in sorghum variety selection and breeding. In this context, combining ability and heterosis analysis were assessed using 14 restorer lines and seven cytoplasmic male sterile (CMS) lines in 2019 and 2020. The analysis of variance of all cross combinations had highly significant differences for all characters studied, which indicated a wide variation across the parents, lines, testers, and crosses. Combining ability analysis showed that the general combining ability (GCA) and specific combining ability (SCA) of the different parents were differed significantly among different traits. Most combinations with high SCA also showed high GCA in their parent lines. The heritability in the narrow sense of grain weight per panicle and grain yield was relatively low, indicating that the ability of these traits to be directly inherited by offspring was weak, that they were greatly affected by the environment. The better-parent heterosis for plant height, grain weight per panicle, panicle length, and 1000-grain weight was consistent with the order of mid-parent heterosis from strong to weak. The GCA effects of two lines 10480A, 3765A and three testers 0-30R, R111, and JY15R were significant for the majority of the agronomic traits including grain yield and might be used for improving the yield of grains in sorghum as parents of excellent specific combining ability. Seven strongly heterotic F1 hybrids were screened; of these, hybrids 3765A × R111, 1102A × L2R, and 3765A × JY15R showed significant increases in seed iristectorigenin A content and will feature into the creation of new sorghum varieties rich in iristectorigenin A.

Evaluation of reciprocal F1 crosses of Fayoumi with two exotic chicken breeds 2: additive and non-additive effects on egg quality traits

The current study evaluates additive and non-additive genetic variances for egg quality traits in six genotypes generated through pure mating and reciprocal crossing of Fayoumi (FM) with Koekoek (KK) and White Leghorn (WL). For each genotype, measurements were taken on 30 eggs randomly sampled at 32, 36, and 40 weeks of age to evaluate both external and internal egg quality parameters. The results revealed significant differences (P < 0.001) among the genotypes in all external quality traits and most internal quality traits, including yolk weight (YW), albumen weight (AW), and yolk height (YH). The results also showed that variations due to purebred effect (PE), general combining ability (GCA), maternal effect (ME), and specific combining ability (SCA) were significant in most traits, which reflects that both additive and non-additive variances are important for the inheritances of the parameters investigated. In most of the traits, the ME and PE were higher in KK and WL, while GCA was higher in KK and FM. The FM x WL had higher SCA than FM x KK. The results suggest the likelihood of genetic improvement in these genotypes through selection and crossbreeding strategies and/or a combination of the two.

Combining Ability and Heterosis among Bottle Gourd [Lagenaria siceraria (Molina) Standl.] Selections for Yield and Related Traits under Drought-Stressed and Non-Stressed Conditions

Bottle gourd [Lagenaria siceraria (Molina) Standl.] is cultivated for multiple utilities, including as a leafy vegetable, for fresh and dried fruits and seeds. It is an under-researched and -utilized crop, and modern varieties are yet to be developed and deployed in sub-Saharan Africa (SSA). There is a dire need for pre-breeding and breeding of bottle gourds for commercialization in SSA. Therefore, this study aimed to determine the combining ability and heterosis among selected genotypes of bottle gourd for fruit yield and related traits under drought-stressed and non-stressed conditions to select the best parents and hybrids. Eight preliminarily selected and contrasting parents with drought tolerance were crossed using a half-diallel mating design. The 8 parents and 28 crosses were evaluated under non-stressed (NS) and drought-stressed (DS) conditions across two growing seasons (2020/21 and 2021/22) using a 6 × 6 alpha lattice design with three replicates. Data were collected on fruit yield and related traits and subjected to analysis of variance, combining ability and heterosis analyses. Significant (p &lt; 0.05) specific combining ability (SCA) and general combining ability (GCA) effects were computed for fruit yield per plant (FYPP). The SCA × environment and GCA × environment interaction effects were highly significant (p &lt; 0.001) for FYPP and SYPP. The results suggest that genetic effects were affected by the test environment. Parental genotypes BG-58 and GC recorded positive and significant GCA effects for FYPP under the DS condition, whereas GC recorded positive and significant GCA effects for FYPP under the NS condition. The two genotypes are ideal breeding parents for population development to select genotypes with high fruit and seed yields. Crosses BG-27 × BG-79, BG-79 × BG-52, BG-79 × BG-70, BG-80 × BG-70, BG-80 × GC, and BG-70 × GC recorded high and positive SCA effects for FYPP and SYPP under DS condition. Crosses BG-81 × BG-52, BG-81 × GC, BG-27 × BG-79, BG-27 × GC, BG-79 × GC, BG-80 × BG-70, BG-81 × BG-58, BG-27 × BG-80, BG-27 × BG-58, BG-79 × BG-52, BG-52 × BG-58, BG-80 × BG-58, and BG-58 × BG-70 recorded high and positive SCA effects for FYPP and SYPP under NS condition. Crosses BG-80 × BG-58, BG-27 × BG-79, BG-79 × BG-52, BG-27 × BG-52, and BG-52 × BG-80 showed high and positive mid- and better-parent heterosis under DS condition for FYPP and SYPP. Crosses BG-27 × GC, BG-79 × GC, BG-27 × BG-58, and BG-27 × BG-79 showed high and positive mid- and better parent heterosis under NS condition for FYPP and SYPP. The newly selected families are recommended for multi-environment evaluation forrelease and commercialization in South Africa or similar agroecologies.

Combining Ability of Quantitative Traits in Snake Gourd (Trichosanthes Cucumerina Var. Anguina)

The present study was carried out on snake gourd having seven diverse genotypes (TC 01, TC 05, TC 24, TC 33, TC 02, TC 46 and TC 53) used as parental lines and their 21 crosses generated from 7 × 7 half-diallel fashion at Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) during March to June 2019 following RCBD with three replications. The aim of the study was to determine general combining ability (GCA) and specific combining ability (SCA) for fruit yield and its related traits including fruit quality traits. General prediction ratio (GPR) of these 14 traits was greater than 0.5 (50%), indicating predominance of additive gene effects over non-additive gene effects. The estimates of GCA for 19 quantitative traits revealed that the genotypes P2 and P6 were good general combiners for promoting earliness as well as most other important characters viz., number of fruits/ plant, individual fruit weight and fruit yield/ plant/ hectare; P2 and P6 were also good for fruit length and fruit diameter, respectively whereas, P4 was good for main vine length and number of nodes on main vine while, P3 was superior for long fruit and 100-seed weight whereas, P5 was good for number of seeds/ fruit and P1 good for less fruit fly infestation including individual fruit weight and fruit length. The most promising specific combiners for fruit yield, quality and yield components were from the 13 crosses viz., P1 × P2, P1 × P3, P1 × P4, P1 × P7, P2 × P3, P2 × P5, P2 × P6, P2 × P7, P3 × P7, P4 × P5, P4 × P6, P4 × P7 and P5 × P7. Out of 13 crosses only two crosses namely, P1 × P2 and P2 × P6 had both the good general combiner parents (high × high). These two crosses were therefore, amenable for improvement of the respective traits through pedigree selection. Remaining 11 crosses displaying high SCA effects for different traits were observed to be derived from parents having various types of GCA effects (high × medium, high × low, medium × low and low × low). The results of 13 crosses therefore, indicate the operation of additive × additive, additive × dominant and/ or dominant × dominant gene interactions for the genetic control of expression of the relative traits.&#x0D; Bangladesh J. Agril. Res. 46(4): 491-510, December 2021

Heterosis and combining ability of iron, zinc and their bioavailability in maize inbred lines under low nitrogen and optimal environments

Iron (Fe) and zinc (Zn) nutrient enrichment of staple crops through biofortification can contribute to alleviating micronutrient deficiency in sub-Saharan Africa. A line × tester mating design was used to determine the general combining ability (GCA), specific combining ability (SCA) and heterosis for grain yield, iron, Zn and phytic concentration of six lines crossed with three testers. Lines and testers were selected for high, intermediate and low mineral content. The F1 hybrids and parental lines were evaluated under low nitrogen (N) and optimum conditions across four environments over two seasons. Under low N conditions, Fe and Zn concentration in grain, and grain yield of genotypes were reduced by 9%, 9%, and 59%, respectively. However, phytic acid concentration in grain was increased by 10% under low N conditions. Both additive and non-additive gene effects were important in controlling Fe, Zn and phytic acid concentration in grain and grain yield of maize under both N conditions. The preponderance of GCA effects indicates the importance of additive gene effects in the inheritance of grain yield. Line GCA effects were more sensitive to N conditions across the environments than the tester GCA. High and significant positive SCA effects for grain yield, Fe and Zn content under low N conditions, would be a good indicator of possible heterosis in these traits. Hybrid CBY101 LM-1600 × CBY358 LM-1857 had high and significant positive SCA for grain yield under low N conditions and is a promising candidate for production in low N environments. CBY358 LM-1857 (tester) and CBY102 LM-1601 (line) are a good general combiners for Fe, Zn and GY can be used as parents in future maize hybrid breeding programs to develop high-yielding maize genotypes with high Fe and Zn content.

Combining Ability Studies on Growth and Improved Leaf Yield Traits in Mulberry, Morus spp.

The study was conducted to evaluate combining ability for growth, quality and yield parameters in mulberry at the field germplasm existed at the Department of Sericulture, UAS, GKVK, Bangalore. Twenty one F1 hybrids was developed by crossing seven lines with three testers according to line x tester design. and assessed using randomized complete block design with three replications. Results revealed that analysis of general combining ability showed the higher magnitude of specific combining ability (SCA) variance than general combining ability (GCA) variance for most of the characters, which indicates the presence of non- additive gene action for most of the traits except for number of branches per plant, number of leaves per plant, and single leaf area. Among seven lines, M. cathyana, MI-47, M. laevigata, MI-494 were found to be best general combiners and in testers V1, MI-66 were found best general combiners with high GCA effects. Among twenty one crosses, BC-259 × MI-66, M. indica × MI-66, M. laevigata × V1 and M. indica × C-776 were found to be superior performers with high SCA effects.

Analysis of hybrid combining ability for growth and multiple stress tolerance traits in the Pacific white shrimp, Litopenaeus vannamei

To identify optimal mating combinations for Litopenaeus vannamei, a linear mixed model was used to estimate the general combining ability (GCA) and specific combining ability (SCA) for growth and multiple stress tolerance [high salt (35‰), low pH (6 ± 0.1), and high ammonia nitrogen (70 mg/L) co-stress] traits in 47 combinations of L. vannamei. The results showed that the SCA in the parents played a dominant role in the offspring traits. The highest GCAs were observed for females of strain O and males of strain B (0.602 and 8.889, respectively), indicating that the dams of strain O and sires of strain B could be used as maternal and paternal lines to increase multiple stress resistance in the next generation. The growth traits of the hybrid combination strain G♂ × strain H♀ exhibited the highest degree of heterosis (9.838%–46.518%) and a generally high SCA (0.643–8.596) among all mating combinations. The SCA was the highest for the strain N♂ × strain O♀ multiple stress tolerance (30.131), while the heterosis for that combination strain was the third-highest. The combinations of strain G♂ × strain H♀ and strain N♂ × strain O♀ can be used as candidate combinations for rapid growth and multiple stress tolerance, respectively.

Establishment of heterotic groups for hybrid wheat breeding

<p indent="0mm">Hybrids utilized in maize and rice production are excellent examples of enhancing crop yield to meet the demand of the increasing world population and climate change. Similarly, hybrid wheat should provide an avenue to increase wheat yield and stress tolerance. Heterosis of wheat is relatively weak due to its allopolyploidy, narrow genetic base between varieties, and long-term varietal selection. The construction of wheat heterotic groups can improve hybrid parental breeding and selection, increase the genetic difference between parents, and enhance the performance of hybrids. To form heterotic groups, it is necessary to understand how heterotic groups are structured. The genetic mechanism of heterosis is not completely understood at present. Research shows that there is no clear relationship between heterosis-related QTL and crops. Also, there is no fixed mode of heterosis in a species. Because multiple genes control heterosis, selection with molecular markers is difficult. Heterosis can be largely attributed to non-additive effects of genes and specific combining ability (SCA) of hybrid combinations. High general combining ability (GCA) of parents plays an important role in maintaining strong heterosis between heterotic groups. Therefore, wheat heterotic group development needs to increase the GCA of parental lines within each heterotic group and select hybrid combinations with high SCA. Some desirable traits for a male heterotic group include tall or medium plant height, heavy pollen production, and strong anther extrusion. Desirable traits for female parents include dwarf or semi-dwarf plant height and large glume opening angle. Disease resistance is important in both male and female groups. Commercial production of hybrid wheat is possible only through the use of male sterility systems. Male sterility in the female parents must be restored by genes in the male parent. Pedigrees, phenotypes, combining ability, genetic distances, and genomic prediction can be used to develop heterotic groups. Genomic prediction can be used to predict heterosis and identify potential heterotic patterns/groups existing in a large number of materials, and, therefore, guide selection of parent lines for development of excellent hybrids. However, the prediction accuracy of statistical models needs to be improved. Utilization of materials from wheat core collection in genomic prediction will facilitate the formation of the training population, and has the potential to improve the prediction accuracy. Recurrent selection in both male and female groups plus reciprocal recurrent selection based on genome prediction can be used to improve wheat heterotic groups. The process of constructing heterotic groups in wheat includes primary population classification, prediction and improvement of heterotic groups, and identification of the best hybrid combination. Development of heterotic groups adaptable to different wheat production regions may utilize both domestic high performing varieties and foreign elite wheat germplasm. Wild relatives with unique traits may also facilitate hybrid wheat breeding and production in China.

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)

Genetics of nitrogen use efficiency and its component traits under nitrogen-rich environment in wheat (Triticum aestivum)

Minimizing the footprints of overuse of nitrogen (N) on the ecosystem is the need of an hour. There is little information on the genetic inheritance of NUE and its component traits. The present study was therefore designed to study the genetic behaviour of NUE traits under abundant N supply. Diallel analysis of 21 F1 along with 7 parents was carried out for NUE traits, viz. shoot dry weight (SDW), root dry weight (RDW), maximum root length (MRL), N% in shoot, gram N in shoot (gN) and nitrogen use efficiency (NUE) under high N in hydroponic condition. Analysis of variance revealed significance for both general combining ability (GCA) and specific combining ability (SCA) for all NUE traits indicating the importance of both additive and non-additive gene action for these traits. Baker's ratio revealed a preponderance of additive genes over non-additive for SDW, RDW and MRLsuggesting thereby effectivity of selection for SDW, RDW, gN, and MRL in the early segregating generation of high GCA lines can improve NUE under high N. Crosses with high SCA effects for SDW, RDW, gN and N% were from the parent combination of high × low GCA effects, whereas for MRL, low × low GCA parents resulted in crosses with high SCA effect indicating the dispersal of favourable alleles in the different parents. Our study indicates the feasibility of improvement of NUE through direct selection for the component traits under N rich environment.

Studies on combining ability for grain yield and related traits in advanced breeding lines in rice (Oryza sativa L.)

The present investigation was undertaken to study the combining ability using 10 lines and 3 testers crossed in Line × Tester mating design. Resulting 30 F1’s were evaluated along with their parents in a replicated trial using randomized block design during Kharif season 2016-17 at Norman E. Borlaug Crop Research Centre Pantnagar, Uttarakhand, India. Genotypes were evaluated for grain yield per plant and its contributing characters. Among the lines UPR3912-21-2-1 and tester NDR359 exhibited a high general combining ability (GCA) for most of the characters under the study. The per se performance and specific combining ability (SCA) effects were in agreement with each other for seven hybrids namely Pant Sugandh Dhan17×NDR359, PD26×NDR359, PR113×NDR359, PD26×NDR359, PD26×PD24, Pant Sugandh Dhan17×PD24, PR113×PD24 for days to 50% flowering, the number of tillers, dwarfness, the number of panicles, panicle length, grain length and 1000 grain weight respectively. Cross PD26×NDR359 exhibited high SCA for number of panicles and both the parents were good general combiner for this character.

Combining ability in maize hybrid for yield-related traits and silage production

Maize cultivars developed for silage production are desirable because ensiling enables the production of high-quality feed and, increases farmers profit. Diallel cross is an efficient and advantageous mating technique that allows the selection of the best parents and crossings. The objective of this study was to estimate the general combining ability (GCA) and specific combining ability (SCA) of hybrids and their parents and to evaluate promising hybrid crosses that can be used in breeding programs. Six genotypes were crossed in a complete diallel system. Fifteen hybrid combinations, six parents, and three commercial controls were evaluated in the 2017/2018 growing season in the north and northwest regions of Rio de Janeiro state, Brazil. Nine agronomic traits were analyzed at the silage stage: plant and ear height, stem diameter, stand, husk covering, number of cobs, husked ear weight, unhusked ear weight, and fresh mass yield. The study employed a completely randomized block design with four repetitions. The parents UENF 2210, Piranão 12, and UENF 2208 presented higher GCA values for fresh matter yield and were indicated for the generation of single cross (F1) hybrids. The parental combinations of UENF 2208  Piranão 12, UENF 2208  UENF 2205, and UENF 2209  UENF 2205 had high SCA for most of the evaluated traits and were promising for the use in breeding programs. The crosses with higher average yield were UENF 2208  Piranão 12, UENF 2210  Piranão 12, and UENF 2208  UENF 2205

General and specific combining ability for cane yield and implications for sugarcane breeding

AbstractGeneral combining ability (GCA) referencing additive genetic effects and specific combining ability (SCA) referencing nonadditive effects have been applied for decades in maize (Zea mays L.) breeding and other crops to produce greater genetic gains in crop breeding. This study examined the magnitude of GCA and SCA for cane yield and evaluated potential for application in sugarcane (Saccharum spp.) breeding. Data were collected from unselected first‐stage breeding populations sourced from the irrigated, midlands (high‐altitude), and coastal breeding programs of the South African Sugarcane Research Institute. Cane yield data calculated from number of stalks, stalk height, and stalk diameter was analyzed using best linear unbiased prediction (BLUP) analysis where female and male effects (GCA) and female × male interaction effects (SCA) were defined as random effects. There were significant (P &lt; .05) female but nonsignificant male effects. Female × male interaction was highly significant (P &lt; .001) and larger than both female and male effects, indicating higher SCA than GCA. Specific combining ability variance was 24% (midlands), 31% (coastal), and 57% (irrigated) higher than GCA. Genotypes with low GCA produced higher SCA. Crosses from parents originating from different breeding backgrounds produced higher SCA than those from the same backgrounds. Crosses with significant SCA produced 24–42% greater cane yield than those with nonsignificant SCA. Using GCA to develop parents with high breeding values and SCA to evaluate parent cross combinations will maximize exploitation of heterosis in sugarcane breeding. The results suggest the possibility to develop heterotic groups that are diverse and complementary as a strategy to optimize utilization of SCA.

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.

Study of combining ability of meadow clover varieties for breeding purposes in the conditions of the Volga-Vyatka region

The article presents the results of research work on the assessment of general combining ability (GCA) and specificcombining ability (SCA) in 14 varieties of meadow clover (Trifolium pratense L.) of various ecological and geographicalorigin (Russia, Belarus). The study was aimed at identifying the best varieties according to productivity indicators for inclusion into the breeding process in the conditions of the Volga-Vyatka region. The study of initial cultivars and their hybridforms F1 was carried out in the field experiment of 2009 with two-year use of grass stand (2010, 2011). The characteristics ofcultivars according to the main morphological and biological characteristics (winter hardiness, length of the vegetative period, plant height, grass stand vigour) and economically significant indicators (collection of raw and dry phytomass, seed yield)in comparison with the zoned Dymkovsky variety are given. All varieties showed high winter hardiness in the conditions of theKirov region (more than 79 %). By productivity of green mass the varieties Karmin, Trio, Stodolich (Russia) were selected.They provided significantly high productivity for 2 years of grass stand use (5.52-5.81 kg/m2, +2.01-2.30 kg/m2to standard)and were characterized by medium value of GCA (104.2-109.6 %) and very high SCA (123.7-139.3 %). According to the totalcollection of dry phytomass, the best varieties were Karmin and Gefest (Russia) with a significantly high level of productivity(1.28; 1.29 kg/m2, +0.49; 0.50 kg/m2to standard), medium GCA (102.4; 103.2 %) and very high SCA (133.3; 134.4 %). By seedyield, the most productive Russian varieties are Stodolishchensky, Trio and Svetlyachok (74.2-82.6 g/m2, +8.8-17.2 g/m2tostandard) with very high GCA (125.5-139.8 %) and SCA value of medium and high level (106.6-118.7 %). According to theresults of the study, for further breeding work the following meadow clover cultivars of Russian research institutes breeding were included as components of new polycross populations: early-matured Karmin and Trio, late-matured Gefest andSvetlyachok.

Diallel Analysis and Heritability of Grain Yield, Yield Components, and Maturity Traits in Cowpea (Vigna unguiculata (L.) Walp.).

Information on combining ability and reciprocal effects (REC) facilitates efficient utilization of genetic materials in a breeding program. This study was conducted (at the CSIR-Savanna Agricultural Research Institute, Ghana) to determine general combining ability (GCA) and specific combining ability (SCA), heritability, genetic advance, GCA, and SCA effects as well as the relationship between parents per se performance and progenies for yield components and maturity traits in cowpea. The test populations were derived using a 5 × 5 complete diallel cross of parents with different yield attributes and maturity durations. The results indicated that GCA was predominant for number of days to 90% pod maturity, plant height at maturity, and hundred-seed weight. This showed that genes with additive effects conditioned these traits. Padi-Tuya, Songotra, and IT86D-610 were identified as good general combiners for grain yield, while Sanzi-Nya was identified as a general combiner for developing extra-early duration cowpea varieties. Crosses Songotra × Sanzi-Nya, SARC-1-57-2 × IT86D-610, Songotra × SARC-1-57-2, and Padi-Tuya × Songotra were identified as good specific combiners for days to 50% flowering, pod length, pods per plant, pod yield, grain yield, and seeds per pod. The findings from this study provide useful information on the inheritance of early maturity and yield traits in cowpea. This can be exploited to develop high yielding and early maturing cowpea varieties as climate smart strategy to mitigate climate change via breeding methods such as pedigree selection and marker assisted backcrossing (MABC). Pedigree selection method is being used to develop varieties from the hybrid with high and significant SCA for grain yield, whereas the development of extra-early duration varieties via MABC with Sanzi-Nya (general combiner for earliness traits) as a donor parent is ongoing.

English

Maize is an important staple food for most Ethiopians, but the national average productivity of maize is below that of the world. Development and cultivation of high yielding maize hybrids can improve maize productivity and production. Having information on combining ability and heterosis of maize inbred lines is important for the development of high yielding maize hybrids. The objectives of this study were to identify good hybrids based on grain yield and yield related traits, to estimate the general combining ability (GCA) and specific combining ability (SCA). Thirteen inbred lines were crossed in 2017 with two line testers using a line by tester mating design. The resulting 26 crosses were evaluated in a randomized incomplete block design (RCBD) with three replications during the main rainy seasons between June and November, 2018 at Bako, Ethiopia. In addition, the 13 parental lines including the two tester lines were evaluated using RCBD with three replications in a separate trial. Analysis of variance (ANOVA) showed that mean squares due to crosses were highly significant (P&le;0.01) for most of the traits studied, except ear aspect. Also mean square due to line was significantly different (P &lt; 0.01 or P &lt; 0.05) in all studied traits except days to anthesis (AD) and ear aspect (EA). The overall mean grain yields (GY) of the hybrids were 6.32 t/ha ranging from 5.21 to 8.19 t/ha. L7 had the lowest negative GCA for grain yield whereas L6 had the highest positive GCA. Among the crosses with high positive SCA, estimates showed high mean grain yield, which implied good correspondence between SCA effects and mean GY. The result obtained in this study could be useful to design for developing high yielding hybrids and synthetics adapted to the mid altitude sub humid agro ecologies of Ethiopia. &nbsp; Key words: Grain yield, maize inbred lines, line by tester, general combining ability, specific combining ability.

Biplot analysis of diallel crosses for yield and some of morphological traits in wheat

A study of combining ability for improving bread wheat yield and yield components was carried out via genotype plus genotype × environment (GGE) biplot. Six bread wheat genotypes were used to obtain F1 in a diallel cross matings at the Gachsaran Field Station, Dryland Agricultural Research Institute during 2012–2013 cropping seasons. Analysis of variance indicated significant effects of genotypes, general combining ability (GCA) and specific combining ability (SCA) for all of the studied traits. The highest values of plant height (108.15 cm), peduncle length (33.95 cm) and grain yield (265.5 g m−1) were obtained in g6 (DAMARA-6 ICW99-0427-8AP-0AP-0AP-3AP-0AP). GGE biplot analysis showed that g4 (Kouhdasht) and g6 (DAMARA-6 ICW99-0427-8AP-0AP-0AP-3AP-0AP) were as the best general combiners for days to maturity, plant height and grain yield, whereas g1 (Karim) had the highest GCA effects for spike length and thousand grain weight, and g3 (Aflak) showed the highest GCA effects in terms of peduncle length. Meanwhile, g6 showed large SCA effects for thousand grain weight and grain yield, while g4 had high SCA effects for spike length. g5 (PASTOR/2*SITTA//PBW343*2/KUKUNACMSS04Y00333S-099Y-099ZTM-099Y-099 M-3WGY-0B) had large SCA effects for peduncle length. Because of significant effects of mid-parent heterosis for grain yield, g4 × g6 was considered as the best possible cross for improvement of this trait. Based on the results of present study, GGE biplot indicated good potential for identifying suitable parents and heterotic crosses and the best hybrids according to diallel mating design.

Inheritance and combining ability of grain yield in half diallel barley population

Studies on the genetic control of grain yield are of great importance for devising effective breeding programmes for yield gain in barley. Hence, inheritance of grain yield, heterosis and combining ability was investigated in barley population obtained from half-diallel crossing among 7 parental lines. The analysis of variance revealed that mean squares due to genotypes were highly significant for grain yield indicating wide diversity among the parental materials usedin the study. Mean squares of general combining ability (GCA) and specific combining ability (SCA), the ratio of GCA to SCA mean squares and portion of additive and dominance variances showed, the importance of both additive and non-additive gene effects for grain yield. The non-significant ratio of GCA to SCA mean square highlighted that non-additive gene effects were more important than additive effects. Distribution of dominant and recessive alleles in parentswas asymmetrical and parents possess the majority of recessive alleles. Since an average degree of dominance has values greater than 1, which indicated the over-dominance type of gene action in the inheritance of the grain yield. The parent BHS400 was considered suitable according to its yield capacities and general combining ability effects. Only 2 crosses viz., BHS400 X RD2660 and BHS400 X RD2552 had significantly higher grain yield than that of the check variety (BHS400), high significant SCA values and high significant useful heterosis values. Considering average narrow-sense heritability and over-dominant effects in the genetic control of grain yield it is better to postpone selection for this trait until advanced breeding generations. Doi.org/ 10.25174/2249-4065/2018/83278

Genetic control of aluminum tolerance in tropical maize germplasm

ABSTRACT Aluminum (Al) toxicity is the most limiting factor to maize crop productivity in acid soils. Therefore, the understanding of inheritance of Al tolerance in maize is important for the developmentof more adequate procedures for Al tolerant genotypes selection. In this sense, the objectives of this study were to determine the inheritance, and the general (GCA) and specific combining ability (SCA) for Al tolerance in tropical maize. First, we evaluated diallel crosses of maize from landrace and hybrid germplasms for Al tolerance through the minimal solution methodology. The DIF data (root growth difference) were analyzed by Griffing diallel model. Later the additive-dominant genetic model proposed by Mather and Jinks (1971) was used to estimate the genetic effects. The results of the diallel analysis showed greater variability associated with the estimates of the SCA for both germplasm. The diallel crosses involving the V 06 (Dente de Ouro 2) landrace stood out by high SCA and GCA for Al tolerance. The generation mean analysis indicated quantitative inheritance of Al tolerance in this germplasm, with most of the variance explained by the additive effects. The heritability in the narrow sense varied from 47% to 71%, indicating the possibility of genetic gain with the selection of tolerant genotypes in F2 generation. Additive gene action associated with intermediate heritability and quantitative inheritance demonstrates the possibility of genetic gains with artificial selection for Al tolerance in this maize germplasm.