Positive General Combining Ability Effects Research Articles

Combining ability analysis of common bean (Phaseolus vulgaris L) genotypes for resistance to bean fly (Ophiomyia spp.), and grain yield and component traits

The bean fly (Ophiomyia spp.) is the most destructive insect pest of common bean (Phaseolus vulgaris L.) causing significant yield losses. The objectives of this study were to determine the combining ability effects and deduce gene action controlling the inheritance of bean fly resistance and agronomic traits among common bean genotypes, and to select superior genotypes for breeding. Eight selected complementary parents were crossed using a half-diallel mating design to derive new families. Parents and 28 F2 families were evaluated in two locations using were evaluated in two locations using a 6 × 6 lattice square design with two replications. Bean fly resistance parameters such as bean fly damage severity (BDS), pupae count (PC) and plant mortality rate (PMR) and agronomic traits such as days to 50% flowering (DTF), days to maturity (DTM), number of pods per plant (NPP), number of seed per pod and grain yield (GYD) were collected. Results revealed significant genotype × location interaction effects on resistance parameters and agronomic traits allowing selection of unique families adapted to different production environments. There were negative correlations between grain yield (GYD) and bean fly damage severity (p < 0.01, r = − 0.60), pupa count (p < 0.01, r = − 0.34) and plant mortality rate (p < 0.01, r = − 0.53), implying that direct selection for bean fly resistant genotypes would improve GYD. Genotypes A429 and A55 exhibited negative general combining ability (GCA) effects for bean fly damage parameters and positive GCA effects for GYD. Good combiners for number of pods per plant (NPP) and GYD were the genotypes A55, MW365 and Sinoni, while MW466 exhibited desirable GCA effects for days to 50% flowering (DTF) and days to 90% maturity (DTM). These parental lines with desirable GCA effects for bean fly resistance and agronomic traits were selected for future breeding. Families such as Sinoni/A55, Kabanima/A55 and MW365/Kabanima showed desirable BDS, PC and PMR (SCA) effects for bean fly resistance and grain yield. Families such as Kabanima/A55, Sinoni/A55 and NUA45/MW365 exhibited desirable and significant SCA effects for traits such as NPP, number of seeds per pod (NSP) and GYD. Families with desirable SCA effects will be utilised in selecting desirable recombinant inbred lines and breeding populations for improving bean fly resistance and agronomic performance. The Baker’s ratios indicated that additive gene effects were more important for bean fly resistance and GYD. Recurrent selection would be the best strategy for improving bean fly resistance and grain yield using this germplasm.

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.

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.

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.

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.

Combining Ability of Early-Maturing Yellow Maize Inbreds under Combined Drought and Heat Stress and Well-Watered Environments

Grain-yield potential of maize (Zea mays L.) is limited by the harsh climatic conditions during dry seasons in the savanna of sub-Saharan Africa (SSA). One hundred and five hybrids derived from diallel crosses involving 15 early-maturing yellow maize inbreds were screened under combined drought and heat stress (CDHS) and well-watered (WW) conditions at four locations representative of the dry savannas of Niger, 2012–2014. The objective of the study was to examine the general combining ability (GCA) effects of the inbred lines and specific combining ability (SCA) of the crosses under CDHS and WW environments, assess yield and stability of the derived hybrids under contrasting environments and investigate inter-relationships among traits of the hybrids under contrasting environments. GCA and SCA effects for grain yield and other measured traits were significant, with preponderance of GCA effects over SCA effects under both the CDHS and WW environments. Inbred ENT 13 possessed positive and significant GCA effects for grain yield under both CDHS and WW environments indicating that the inbred could be used for developing outstanding hybrids with good levels of tolerance to CDHS. This also implied that the inbred line could serve as invaluable genetic resource for introgression of favorable alleles into tropical early-maturing maize populations for accelerated genetic gains from selection for improved grain yield. Hybrids ENT 13 × TZEI 167 and TZEI 157 × ENT 13 were the most stable and among the highest yielding hybrids across research environments. These outstanding hybrids could be tested extensively for commercialization in SSA to improve food security. Plant and ear aspects and days to 50% silking could be combined with grain yield in a selection index for improvement of yield under CDHS without yield penalties under WW environments.

Diallelic Analysis of Tropical Maize Germplasm Response to Spontaneous Chromosomal Doubling.

Chromosome doubling is an important step in the production of maize doubled haploid (DH) lines to induce fertility in the male and female reproductive organs of haploid plants. Chromosomal doubling is routinely accomplished by treating haploid seedlings with mitosis-inhibiting chemicals. However, chromosomal doubling involves several labor-intensive steps and toxic chemicals. Spontaneous chromosomal doubling without any chemical treatments occurs at high frequency in haploids from a few maize genotypes. This study focused on elucidating the genetic components of two traits important for using spontaneous doubling in maize-breeding programs, namely, haploid male fertility (HMF) and haploid fertility (HF). In two different sets of diallel crosses, haploids were derived and assessed for HMF and HF in two environments in replicated trials. The results revealed significant genotypic variations for both traits. The general combining ability (GCA) and specific combining (SCA) were significant for both traits. Significant and positive GCA effects of up to 14% and 9% were found for HMF and HF, respectively. No significant reciprocal effects and genotype-by-environment (G×E) interactions were found for HF in both experiments, but HMF showed significant effects for both in one of the experiments. The GCA effects were more important than the SCA effects for HMF and HF across environments, implying that selection could facilitate their improvement. The high correlations between F1-hybrid performance and mid-parent values, as well as that between F1-hybrid performance and GCA effects, also supports the assumption that these traits are controlled by a few genes. SCA effects also played a role, especially when lines with low spontaneous doubling were used as parents. Overall, spontaneous doubling can be introgressed and improved in elite germplasm with selection, and it has the potential to be employed in DH pipelines.

HETEROSIS AND COMBINING ABILITY FOR YIELD AND FIBER QUALITY IN COTTON (GOSSYPIUM BARBADENSE L.) USING HALF DIALLEL MATING SYSTEM

The present study was carried out at Sakha Agricultural Research Station, Cotton Research Institute, Agricultural Research Center, Egypt, during the two successive seasons 2018 and 2019. Six cotton varieties belong to (Gossypium barbadense L.). Three of them are Egyptian cotton varieties; Giza 89, Giza 93 and Giza 96. The other three varieties are Pima S4, Pima S6 and Suvin. They were crossed in a half diallel mating to produce 15 F1 hybrids in 2018 season. The F1 hybrids and six cotton varieties were growing in 2019 season in a randomized complete blocks design with three replications. The Results showed that the mean squares of the genotypes, parents, crosses and parents versus crosses were significant and highly significant for all studied traits except No. of bolls/plant at parents and micronaire reading at parents versus crosses. The results illustrated that the mean squares of general combining ability (GCA) and specific combining ability (S.C.A.) were significant and highly significant for all studied traits except micronaire reading at specific combining ability (S.C.A.). The parental genotypes Giza 96 and Giza 89 gave significant (desirable) GCA effects for most yield traits. Giza 96 and Suvin exhibit significant and positive (desirable) GCA effects of some fiber properties. The crosses Giza 89 x Pima S4, Giza 96 x Pima S6 and Giza 96 x Suvin recorded significant and positive (desirable) SCA effects for most yield traits, while the crosses Giza 89 x Giza 96, Giza 96 x Suvinand Giza 89 x Suvin showed significant (desirable) SCA effects for some fiber properties. following crosses Giza 89 x Giza 96, Giza 93 x Giza 96, Giza 96 x Pima S4, Giza 96 x Pima S6 and Giza 96 x Suvindemonstrated desirable heterosis relative to mid- and better-parent for most studied yield traits, also the crosses Giza 89 x Giza 96 and Giza 89 x Suvin indicated desirable heterosis relative to mid- and better-parent for some fiber properties. The results indicated that the non-additive of genetic variances were larger than the additive genetic variance with respect to all studied traits except, lint percentage, boll weight, upper half mean and micronaire reading traits. Generally, Giza 96 and Giza 89 could be used in breeding programs for improving high yielding varieties, while Giza 96 and Suvin could be considered as excellent parents for breeding programs to produce new varieties characterized with best fiber properties.

Combining ability and testcross performance of low N tolerant intermediate maize inbred lines under low soil nitrogen and optimal environments

AbstractLow soil nitrogen (low N) threatens maize production in sub-Sahara Africa (SSA). We examined the mode of gene action conditioning grain yield of intermediate maturing inbreds and evaluated lines in hybrid combinations for high yield, stability and tolerance to low N. Thirty-two sets of inbreds were crossed to three elite testers (87036, 1368 and 9071) to generate 96 F1 hybrids. The testcrosses plus four hybrid checks were evaluated under low (30 kg/ha) and high (90 kg/ha) N environments at three locations for 2 years in Ghana. Significant general combining ability (GCA) and specific combining ability (SCA) effects were detected for grain yield and most measured traits across test environments, indicating that both additive and non-additive gene action governed the inheritance of the traits. GCA effects were greater than SCA effects, indicating that most traits were controlled predominantly by additive gene action and that inbreds with positive significant GCA effects for grain yield and other traits would contribute favourable alleles to progenies across environments. Hybrid CZL 0001 × 9071 possessed high GY, increased EPP, desirable EHT and PLHT and was the highest yielding under each of two research conditions. Significant genetic correlations were observed between GY and PLHT, EPP, EHT, CA and PA implying that improvement of these traits would lead to significant gains in grain yield under low-N conditions. Hybrids CLWN 247 × 9071, ZM523B-29-2-1-1-B*6 × 9071, TZD II 68 × 1368 and P43SCRq Fs100-1-1-8 × 9071 were high-yielding, stable and low-N tolerant and should be tested on-farm and commercialized.

Combining ability study for yield and quality traits in cucumber (Cucumis sativus L.)

Seven cucumber (Cucumissativus L.) genotypes (3 lines and 4 testers) were crossed in a line × tester mating design. The resultant 12 hybrids and their parents were evaluated using Randomised Block Design with two replications during Kharif 2018. Sufficient genetic variability was observed for all the characters under study. In this study, the parents L2 (Koradacherry local), T2 (Orathanadu local) and T3 (Aipatti local) exhibited high positive GCA (General Combining Ability) effects for yield related traits and high negative GCA effects for earliness characters. The parent T2 identified in this study may be used in multiple crossing programme to isolate high yielding varieties. Among the hybrid combinations, L2xT3, L1xT2 and L3xT4 expressed the maximum positive significant SCA (Specific Combining Ability) effects for yield and yield associated characters. In the above cross combinations one parent was a good combiner and the other was an average/poor combiner; hence the hybrids can be exploited for transgressive selection.

Genetic Analysis of Some Agronomic Traits in Okra (Abelmoschus esculentus L. [Moench

Abstract A study was carried out at the Federal University of Agriculture Abeokuta, Nigeria to determine the gene action underlying the inheritance of important agronomic traits as well as the general combining ability (GCA) and specific combining ability (SCA) of the parents and hybrids, respectively. Ten hybrids were developed by crossing five lines to two testers. The hybrids and parents were evaluated on the field in a randomised complete block design replicated three times, and data were collected on days to 50% flowering, number of branches, stem diameter, plant height, pod length, pod width, pod weight, number of pods and pod yield. The data were subjected to line by tester analysis and results showed substantial variability among the genotypes for some of the characters measured. Days to 50% flowering, number of pods and pod yield were largely under additive gene action while non-additive gene action was more important in the inheritance of plant height. Favourable GCA and SCA effects for days to 50% flowering were observed in NGB00356, NGB00326 and NGB00347 × NGB00326, respectively. The tester NGB00326 had a positive and significant GCA effect for number of pods while the highest positive SCA effect for pod yield was found in NGB00297 × NGB00326. Thus, NGB00356 and NGB00326 could be considered as sources of alleles for development of early maturing while the cross NGB00297 × NGB00326 could be exploited for high yielding okra genotypes.

Evaluation of U.S. inbred lines with expired plant variety protection for mid-altitude tropical maize breeding

Maize (Zea mays L.) inbred lines with expired U.S. Plant Variety Protection Act certificates (ex-PVPA) can be an important source of favorable alleles to improve grain yield, root and stalk lodging, drydown, plant architecture, and reduced time to maturity of tropical hybrids. Understanding the heterotic patterns and combining ability of ex-PVPA lines with tropical lines is necessary to design effective breeding strategies using this germplasm. This study evaluated 10 Iowa Stiff Stalk Synthetic (BSSS) and 11 Non-Stiff Stalk Synthetic (NSSS) inbred lines in hybrid combinations with tropical mid-altitude testers in five mid-altitude environments (900–2000 masl) in Mexico and identified six hybrids with grain yield equal or superior to that of the check hybrids. Two NSSS inbred lines: PHR03 and PHN82 had significant (P < 0.01) and positive general combining ability (GCA) effects with inbred lines from CIMMYT’s Tuxpeno heterotic group. Similarly, the BSSS line PHG39 had a significant positive GCA effect (P < 0.05) with non-Tuxpeno lines. The lines PHN82 and PHK29 had positive GCA effects (P < 0.01) under drought stress and could be used as sources of drought tolerance in CIMMYT breeding programs. The mid-altitude lines CML537 and CML539 had positive GCA effects (1.45 and 0.69 t/ha, respectively; P < 0.01) with NSSS lines whereas hybrids of CML384 with BSSS lines yielded 0.64 t/ha (P < 0.01) more than the average of the testcrosses. These results showed that U.S. ex-PVPA lines can increase grain yield of CIMMYT’s tropical mid-altitude hybrids.

Combining ability and heterosis among sorghum (Sorghum bicolor [L.] Moench) lines for yield, yield-related traits, and anthracnose resistance in western Ethiopia

High-yielding sorghum genotypes with farmer-preferred agronomic traits and durable anthracnose resistance are key drivers of productivity and adoption. The objective of this study was to determine combining ability effects and heterosis of selected sorghum lines for yield, yield-related traits, and anthracnose resistance, to identify superior parents and families for further selection and breeding. Nine selected sorghum genotypes with known resistance to anthracnose were crossed, using a 9 × 9 half-diallel mating design. Parents and F1 families were evaluated across two locations, using a randomized complete block design with three replications. Significant (P < 0.01) genotype, location, and genotype × location interaction effects were observed for most traits and anthracnose resistance, indicating mixed performances of the tested genotypes, allowing for further selection. General combining ability (GCA) and specific combining ability (SCA) effects were significant (P < 0.01) for most traits, including anthracnose resistance, indicating both additive and non-additive gene action underlying inheritance of the studied traits. Parental genotypes such as Bt-623, 210903, 234112, and 226057 showed positive and significant GCA effects for grain yield. Parents 74222, 214852, and 71708 showed negative and significant GCA for anthracnose resistance. The following families: Bt-623 × 210903, Bt-623 × 234112, Bt-623 × Chemeda, Bt-623 × Gemedi, 210903 × 234112, 210903 × 71708, 74222 × 234112, 74222 × 226057, 234112 × 71708, 226057 × 214852 and 226057 × 214852 expressing positive SCA effects for grain yield were identified. The following desirable families were selected: 174222 × 234112, Gemedi × 71708, Bt-623 × 234112, Bt-623 × Gemedi, 226057 × 71708, Chemeda × 71708, and Gemedi × 71708 with negative SCA effect and low anthracnose severity. These are useful sorghum populations for resistance breeding or direct production.

MORPHOLOGICAL IDENTIFICATION AND EVALUATE THE COMBINING ABILITY AND HETEROSIS OF SOME INBRED LINES OF MAIZE AND ITS CROSSES

In 2016 five maize inbred lines were crossed in all possible combinations without reciprocals by using a half diallel crosses mating design to obtain 10 single crosses. Parental inbred lines and their F1 single crosses were evaluated through 2017 season to evaluate the role of general and specific combining ability, heterosis and the morphological characteristics. A randomized complete block design with three replicates was used. Results showed that mean squares of genotypes, general combining ability (GCA) and specific combining ability (SCA) were highly significant for all studied yield traits. The GCA/SCA ratio was less than unity for all studied traits, this means that these traits are predominantly controlled by non-additive gene action. Positive significant GCA effects were found for all studied traits. Based on GCA estimates, it could be concluded that the best combiners were Inb 209 and Inb 239 for most of studied traits. This result indicated that these inbred lines could be considered as good combiners for improving yield and its attributes. Positive significant SCA effects were found for all studied traits. Based on SCA effects, the best crosses for ear diameter, 100-kernel weigh and kernel number/row was C1; for ear length was C10 and for ear weight/plant, grain weight/plant and shelling percentage was C8. Results showed positive significant heterosis values for all studied yield traits. The best crosses over both their mid-parents and better-parents for ear diameter and 100-kernel weigh was C2; for ear length and kernel number/row was C5; for ear weight/plant and grain weight/plant was C9 and for shelling percentage was C8.

Testcross performance and combining ability of early maturing maize inbreds under multiple-stress environments

Availability of multiple-stress tolerant maize is critical for improvement in maize production in West and Central Africa (WCA). A study was carried out to (i) assess a set of inbred lines for combining ability under stressed and optimal conditions, (ii) determine the performance of the testcrosses under different conditions, and (iii) identify outstanding hybrids across the conditions. Two hundred and five testcrosses were planted with five hybrid checks under Striga-infested, low soil nitrogen, drought and optimal conditions between 2015 and 2016 in Nigeria. The grain yield inheritance under optimal condition was largely regulated by additive gene effect whereas non-additive gene effects largely regulated grain yield under the three stresses. Four of the inbreds had significant positive general combining ability effects each under low N and drought, and three under Striga infestation for grain yield. The inbreds could be vital sources of beneficial alleles for development and improvement of tropical yellow maize hybrids and populations. Hybrids TZEI 443 x ENT 13 and TZEI 462 x TZEI 10 were high yielding and stable; they out-performed the three early maturing released hybrids in WCA. The new hybrids should be extensively assessed and released in the sub-region to improve food security.

Combining ability and heterosis of selected sweetpotato (Ipomoea batatas L.) clones for storage root yield, yield-related traits and resistance to sweetpotato virus disease

Designed crosses using genetically diverse and complementary genotypes is useful to develop sweetpotato clones with improved agronomic traits. The objective of this study was to determine combining ability and heterosis among selected sweetpotato clones for number of storage roots per plant (NRPP), storage root yield (SRY), dry matter content (DMC) and resistance to sweetpotato virus disease (SPVD) for breeding. Eight selected genotypes were crossed using an 8 × 8 half diallel mating design to generate 28 families which were evaluated along their parents under field condition at three sites using a 6 × 6 lattice design with three replications. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant (P < 0.001) among families. Significant GCA × sites and SCA × sites effects indicated environmental effect on gene action and expression. Parental genotypes Simama and Gairo had positive and significant GCA effects for NRPP. The parents 03-03, Ukerewe and Simama had significant and positive GCA effects for SRY and DMC, respectively. Further, Ex-Msimbu-1 and Gairo displayed negative and significant (P ≤ 0.01) GCA effect for SPVD resistance. The genotypes Gairo, 03-03, Ukerewe, Simama and Ex-Msimbu-1 are promising parents for sweetpotato breeding to improve NRPP, SRY, DMC and resistance to SPVD. Further, the study selected best performing families namely: 03-03 × Simama, 03-03 × Resisto and Simama × Ex-Msimbu-1 which recorded the highest mean storage root yields of 16.1, 16.6 and 17.2 tons/ha combined with high DMC and resistant to SPVD for genetic advancement.

Test cross performance and combining ability of newly introduced quality protein maize (Zea mays) inbred lines for grain yield and agronomic traits evaluated in mid-altitude agro-ecological zones of Ethiopia

Development of quality protein maize (QPM) helps to reduce human malnutrition in areas where maize is the major protein source in the diet. The objective of this study was to estimate combining ability effects of QPM inbred lines for grain yield and yield-related traits. Twenty-one newly introduced QPM inbred lines were crossed with four single cross testers in a line × tester mating design and resulted in 84 F1 progenies. These F1 hybrids, including four checks, were evaluated in an 8 × 11 alpha lattice design with two replications at four locations during 2016. Mean squares due to location, crosses, general combining ability (GCA) and specific combining ability (SCA) were significant for most traits. However, the contributions of GCA sum of squares to the variation among the hybrids were larger than SCA sum of squares, suggesting that the traits were controlled predominantly by additive gene effects. Among the inbred lines, L3, L5 and L10 showed positive and significant GCA effects for grain yield and other agronomic traits. The lines can be used in synthetic variety development. Among crosses, only L3 × T3, L9 × T1 and L15 × T2 revealed positive and significant SCA effects for grain yield, implying the presence of heterosis in these particular crosses.

Heterotic affinity and combining ability of exotic maize inbred lines for resistance to aflatoxin accumulation

Aflatoxin accumulation in maize (Zea mays L.) kernels is a serious economic and health problem that reduces grain quality and nutritional values and causes death to livestock and humans. Understanding the genetic parameters and heterotic responses of exotic maize inbred lines can facilitate their use for developing aflatoxin resistant parents of hybrids in Africa. This study was designed to (1) determine the heterotic affinities of aflatoxin resistant exotic lines, (2) identify exotic inbreds with good combining ability, and (3) determine the mode of inheritance of resistance to aflatoxin contamination in these lines. A line × tester mating design was used to determine combining ability of 12 yellow and 13 white inbreds and classify them into heterotic groups. The inbreds were crossed to two adapted testers representing two African heterotic groups and the resulting testcrosses along with hybrid checks were evaluated in separate trials at two locations for 2 years in Nigeria. General combining ability (GCA) effects were more important than specific combining ability effects for aflatoxin and grain yield. Among 15 exotic inbred lines having negative GCA effects for aflatoxin and 13 with positive GCA effects for grain yield, six combined the two desired traits. Five white and six yellow endosperm testcrosses were found to be good specific combiners for the two desired traits. The exotic lines with negative GCA effects for aflatoxin accumulation will be used as donor parents to develop backcross populations for generating new inbred lines with much higher levels of resistance to aflatoxin accumulation.

English

The genetic potentials of resistance to turcicum leaf blight (TLB), grey leaf spot (GLS), and common rust (CR) disease, grain yield and selected agronomic trait were studied in 45 F1 hybrids from a half diallel following Griffing’s Model 1, Method 4. The 45 hybrids excluding parents were evaluated in 5 × 9 alpha lattice designs with three replications. The study was carried out at Jimma Agricultural Research Center during 2015 cropping season with the objective to evaluate combining ability for turcicum leaf blight, grey leaf spot, common rust disease, grain yield and selected agronomic trait in maize inbred lines. For analysis of variance, days to 50% anthesis, days to 50% silking, turcicum leaf blight, grey leaf spot, common rust disease severity index, days to maturity and grain yield data were collected. Mean square due to general combining ability (GCA) was highly significant (P ≤ 0.01) for all traits, while specific combining ability (SCA) mean square was non-significant except for grain yield, days to 50% tasseling, days to 50% of silking, and days to maturity. This study showed the importance of additive types of gene action in controlling the inheritance of the traits. Among ten inbred lines, L7 and L10 were best combiners for GLS tolerance with the highest negative value of GCA effects and inbred line L7 was the best combiner for TLB and CR tolerance with the highest negative value of GCA effect. Inbred lines L2 and L9 were best combiner for grain yield with the highest positive GCA effect value. Therefore, maize breeding program can engage in hybridization and synthetic variety formation based on the information of inbred lines with high negative value GCA effect for diseases tolerant and high GCA for grain yield. Key words: Combining ability, general combining ability (GCA), inbred lines, specific combining ability (SCA).

Heritability and Combining Ability for Cold Hardiness from Partial Dialleles in Iranian Pomegranate Cultivars

The development of cultivars with broader climatic adaptation has recently become the objective of most fruit breeding programmers. Regarding the importance of genetic control of cold hardiness as an influential characteristic for pomegranate and lacking studies in this area, the genetic control of cold hardiness in pomegranate using a partial mating scheme was studied. Five parents, including ‘Rabab Post Ghermez Neyriz’, ‘Malas Yazdi’, ‘Poost Sefid Dezful’, ‘Malas Pishva Varamin’, and ‘Poost Nazok Torosh Abarkuh’ with different cold hardiness capability were screened following a cold hardiness test in the laboratory and an evaluation of cold injury after natural freezing events in the field. The five screened cultivars were crossed in half-diallel crossing scheme with a total of 10 crosses in the Spring of 2014. Cold hardiness of the parent cultivars and the F1 progenies were investigated using the electrolyte leakage (EL) method. Results showed that both general combining ability (GCA) and specific combining ability (SCA) were statistically significant. The hardiest parent (‘Poost Nazok Torosh Abarkuh’) showed the largest positive GCA effect (1560.59) for winter survival, suggesting that this parent is capable to produce tolerant offspring with high breeding values in crossing programs. The significant SCA in this study suggests that specific crosses should be targeted to produce highly capable offspring. Cross between ‘Poost Nazok Torosh Abarkuh’ and ‘Malas Pishva Varamin’ showed high value for SCA (1661.74), indicating capability for production of tolerant offspring to the cold condition. Furthermore, high broad-sense heritability (0.70) and moderate narrow-sense heritability (0.45) for cold hardiness indicate that a reasonable progress could be made in improvement of this trait through conventional breeding.