Combining Ability Values Research Articles

Heterosis, combining ability and genetic component in okra (Abelmoschus esculentus (L.) Moench) genotypes

ABSTRACT Information on gene action controlling the inheritance of quantitative traits is essential for selecting parents for hybridization and multiline varieties. Twenty hybrids obtained through 5 × 5 diallel mating with their parents were established on Teaching and Research Farm, Federal University of Agriculture, Abeokuta, Nigeria, in September 2018 using Randomized Complete Block Design in three replicates. The plants were observed for numbers of days to 50% flowering, plant height at flowering, stem girth, number of branches per plant, plant height at maturity, number of fruits per plant, fruit weight, fruit length, fruit width, and fruit yield per plant. Data were subjected to variance analysis, General and Specific Combining abilities were estimated, and gene effects and parameter ratios were done using Hayman’s method. Mid- and better-parent heterosis were estimated using Allard’s procedure. Genotype ‘NGB00356’ was the most desirable parent for earliness and the number of fruits per plant, while hybrid ‘NGB00347’ × ‘NGB00356’ was the best hybrid for fruit yield per plant. ‘NGB00356’, with its significant and positive general combining ability value for the number of fruits per plant, can be used as a parent in a hybridization program for yield improvement in okra.

Enhancing yield and oil content in oilseed rape hybrids: Insights from line × tester and SIIG approaches.

The production of high-oil-yielding hybrid varieties is a primary objective in oilseed rape (Brassica napus L.) breeding programs. Biometric genetic experiments such as line × tester provide valuable insights into the genetic structure of traits associated with high oil yield. In this study, 21 winter hybrids of oilseed rape were evaluated, which were generated by crossing three restorers with seven CMS lines. The experiment was conducted using a line × tester experiment based on a completely randomized block design. Phenological, agronomic, yield, and oil yield components were assessed in this study. The ideal genotype selection index (SIIG) methodology was also employed to identify superior hybrids based on all studied traits simultaneously. Significant differences were observed between the obtained hybrids and the check cultivars. Heritability analysis revealed that phenological traits were primarily controlled by additive effects, while agronomic and qualitative traits were mainly influenced by non-additive gene effects. Both broad-sense and narrow-sense heritability exhibited a wide range, underscoring the importance of genetic variance. Notably, the hybrids T1 × L5, T1 × L6, and T3 × L1 showed significant specific combining ability values of 394.74, 541.73, and 1236.79, respectively, making them the top specific combinations for increasing seed yield. Based on the SIIG index, hybrids T3 × L1, T1 × L5, T1 × L3, and T2 × L3 emerged as high-oil-yielding hybrids with desirable agronomic traits. The identified superior hybrids by line × tester and SIIG approaches hold promise for the development of high-yielding oilseed rape cultivars with desirable agronomic traits in oilseed rape breeding programs.

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

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

A Study on the Specific Combining Ability in Several Inbred Lines of Maize

Maize is a cereal crop essential to fulfill the need for food and support global food security programs. Maize hybrid varieties play a very significant role in increasing maize production. Objectives of the research were to obtain a tester, which is consistent in identifying inbred lines with a high specific combining ability, and to obtain prospective crossed-hybrids that have the potential assembling to be maize hybrid varieties. The grain yield showed that the specific combining ability values ranged from -3682.2 to 5251.7. Crosses that have high and positive specific combining ability included lines of JG-11, JG-18, JG-34, JG-01, JG-40, JG-B0, JG-19, and JG-02 with a tester of JG-T00; lines of JG-20, JG-01, JG-03, JG-42, JG-02, JG-46, and tester of JG-T14; lines of JG-24, JG-08, JG-23, JG-26, JG-21, JG-07, and JG-06 with a tester of JG-T15; lines of JG-38, JG-40, JG-35, JG-36, JG-01, JG-51, JG-17, JG-B0, and JG-08 with tester of JG-T22; and lines of JG-07, JG-01, JG-26, JG-24, and JG-18 with tester of JG-T37. There were combinations of 9 crosses between inbred lines and the best testers, including JG-06XJG-T15, JG-51XJG-T22, JG-49XJG-T22, JG-B0XJG-T22, JG-35XJG-T22, JG-38XJG-T22, JG-17XJG-T22, JG-36XJG-T22, and JG-49XJG-37, which are potential as prospective maize hybrids that have high productivity.

Effects of the combining ability on mirador chili (Capsicum annuum L.) populations native to Veracruz, Mexico

Objective: To evaluate the effects of the general and specific combining abilities on the agronomic traits of the native populations of mirador chili and to identify potential genotypes for the genetic improvement of this crop. Design/Methodology/Approach: The general and specific combining abilities were calculated to determine the agronomic traits and yield of five mirador chili populations, using Griffing’s method 2, model I, which includes parental lines and direct crosses. Results: The P1, P4, and P3 genotypes recorded the highest and positive values. They also recorded a significative difference regarding the general combining ability. Meanwhile, the P1×P5 and P4×P5 crosses recorded the highest specific combining ability values. Study Limitations/Implications: We were not able to establish diverse evaluation environments and genomic selection studies using molecular markers. Findings/Conclusions: Information about the yield potential of five mirador chili was generated. These results are important for the development of a genetic improvement program and for the selection of the method that will be used.

Differential Responses to Yellow-Rust Stress Assist in the Identification of Candidate Wheat (Triticum aestivum L.) Genotypes for Resistance Breeding

Yellow rust (YR) globally affects wheat crops. It may turn into an epidemic, resulting in significant yield losses if the environment is suited to YR spread. The provision of resistant wheat cultivars is a sustainable protection strategy against YR. The current study aimed to use a combination of classical analytical tools to identify potential wheat lines through screening under YR stress for utilization in YR-resistance breeding. A total of 14 parents, which included 9 lines and 5 testers, were formed into 45 cross combinations via line × tester mating format. The tested germplasm was grown in a triplicate randomized full-block design, under optimal and yellow rust (YR)-stress conditions. Data were recorded on different morphological, physiochemical, yield and component traits at appropriate crop stages. A pre-combining ability analysis revealed significant inter-genotype variations. A combining ability study identified non-additive gene action in the inheritance of most of the investigated traits. Four potential parents (PR128, AN179, KS17 and WD17) and two crosses (PR128 × WD17 and AN179 × KS17) retained higher combining ability values for yield traits under YR-stress. A cluster analysis based on the overall performance found divergent classes among the screened genotypes. The clustering of different genotypes was shifted under YR-stress, which suggests variable genotypic response. Through factor analysis, we assessed and confirmed genotypes performing consistently under YR-stress. The identified genotypes may be used for disease-resistance breeding in wheat. Based on their positive correlation with grain yield, we suggest the use of peduncle length and tillers per plant as phenotypic markers for wheat selection and breeding. The knowledge base generated through the current study will add to the ongoing research on sustainable wheat breeding program.

Variations and heritability of phenotypic characters in the reblooming bearded iris (Iris germanica L.)

• Longer leaves on non-blooming stems and less flowers on a scape may be two phenotypes for the rebloomers to support twice flowering. • FM1 ( Iris germanica ‘Cornhusker’) was the most ideal maternal parent. • FM2 × M2 ( I. germanica ‘Delta Lady’ × I. germanica ‘HD’) was the ideal cross combination with the reblooming rate being 16.67%. • Length of fall and scape height gained the largest broad-sense heritability (88.03%) and narrow-sense heritability (66.63%), respectively. • There were correlations between the vegetative trait plant height and the floral characters. The reblooming bearded iris ( Iris germanica L.) could bloom in not only spring, but also autumn. The additional blooming seasons bring the phenotypic differences between the once-bloomers and the rebloomers. However, the lack of studies on the rebloomers’ phenotypic variations largely hinders the process of breeding. In this study, ten F 1 populations were produced according to the North Carolina Design II, using five maternal and two paternal parents. After the hybridization, the leaves of non-blooming stems were longer than their parents in all of the F 1 populations, the photosynthesis of which may provide more nutrition for the additional blooming. Furthermore, the fewer flowers on a scape in F 1 could be another phenotype to support twice flowering. The six floral characters (height of individual flower (HF), diameter of flower (DF), length of fall (LF), width of fall (WF), length of standard (LS) and width of standard (WS)) were all largely improved in the cross combination of FM2 × M2 ( I. germanica ‘Delta Lady’ × I. germanica ‘HD’) over both parents. FM2 × M2 was considered as the ideal cross combination after the comprehensive analysis of heterobeltiosis, special combining ability and reblooming rate (16.67%). The general combining ability values showed that FM1 ( I. germanica ‘Cornhusker’) tended to be the ideal maternal parent. LF and scape height gained the largest broad-sense and narrow-sense heritability (88.03% and 66.63%), respectively. The correlations between the vegetative trait (plant height) and the six floral characters (HF, DF, LF, WF, LS and WS) enabled the selection of the large-flower individuals at the stage of vegetative growth. All these results presented a preliminary profile of the phenotypic characters inheritance, and may guide the future breeding of the rebloomers.

Genome-wide dissection of hybridization for fiber quality- and yield-related traits in upland cotton.

SUMMARYAn evaluation of combining ability can facilitate the selection of suitable parents and superior F1 hybrids for hybrid cotton breeding, although the molecular genetic basis of combining ability has not been fully characterized. In the present study, 282 female parents were crossed with four male parents in accordance with the North Carolina II mating scheme to generate 1128 hybrids. The parental lines were genotyped based on restriction site‐associated DNA sequencing and 306 814 filtered single nucleotide polymorphisms were used for genome‐wide association analysis involving the phenotypes, general combining ability (GCA) values, and specific combining ability values of eight fiber quality‐ and yield‐related traits. The main results were: (i) all parents could be clustered into five subgroups based on population structure analyses and the GCA performance of the female parents had significant differences between subgroups; (ii) 20 accessions with a top 5% GCA value for more than one trait were identified as elite parents for hybrid cotton breeding; (iii) 120 significant single nucleotide polymorphisms, clustered into 66 quantitative trait loci, such as the previously reported Gh_A07G1769 and GhHOX3 genes, were found to be significantly associated with GCA; and (iv) identified quantitative trait loci for GCA had a cumulative effect on GCA of the accessions. Overall, our results suggest that pyramiding the favorable loci for GCA may improve the efficiency of hybrid cotton breeding.

Sources, Spectrum, Genetics, and Inheritance of Phaseolus vulgaris Resistance Against Xanthomonas citri pv. fuscans.

Common bean (Phaseolus vulgaris) is one of the most consumed agricultural products in the world. Its production is affected by common bacterial blight (CBB) caused by Xanthomonas citri pv. fuscans and X. phaseoli pv. phaseoli. In this work, we investigated the spectrum, genetics, and inheritance of common bean resistance to X. citri pv. fuscans. Inoculation of nine selected cultivars with an X. citri pv. fuscans strain showed that BRS Radiante and IAPAR 16 were resistant. These two cultivars were also resistant to six X. phaseoli pv. phaseoli strains of different geographic origins, demonstrating their broad-spectrum resistances. BRS Radiante sustained smaller X. citri pv. fuscans populations than two susceptible cultivars. Stomatal densities of IAPAR 16 and BRS Radiante were significantly higher than or not different from susceptible cultivars. BRS Radiante showed the lowest general combining ability values and the combination BRS Radiante × Carioca MG the lowest specific combining ability (SCA) values, revealing the capacity of BRS Radiante to increase resistance to X. citri pv. fuscans. Positive and negative parental SCA values indicated dominant and recessive genes involved in X. citri pv. fuscans resistance. Resistance of the BRS Radiante × Carioca MG cross segregated in a 9:7 ratio in the F2 population, indicating that it is governed by two complementary dominant genes. Maximum likelihood analysis showed that the resistance of BRS Radiante to X. citri pv. fuscans is conferred by a gene of major effect with contribution of additional polygenes. This study contributes with important knowledge on the resistance against CBB in Brazilian common bean cultivars as well as with molecular tools for confirmation of common bean hybrids.

Inheritance of Some Growth and Yield Traits in Bread Wheat Using Line×Tester Analysis

Seven Bread wheat genotypes (Triticum aestivum L.) were used in this investigation. Three genotypes namely (Maroof, Aras, and Hasad) were used as female parents (lines) and four genotypes namely (Alla, Tamuz-2, Adana and Sabr Beg) were used as male parents (testers).The 12 F1’s hybrids with their 7 parents were evaluated during 2018-2019 growing season. Genotypes were crossed in a line×tester matting in Completely Randomized Block Design (CRBD) with three replicates at two Locations; Kanipanka and Qlyasan, at Sulaimani city in Iraqi Kurdistan Region. The pooled analysis of variance confirmed that location had a significant effect on almost all of the studied traits, but it has no effect on grain yield plant-1. The results proved a significant difference between the studied locations in all characters except final yield. At Kanipanka location, Sabr Beg and the cross Maroof×Tamuz-2 granted the highest yield; 26.303 and 23.914 g plant-1respectively.At Qlyasan location Tamuz-2 and the cross Hasad ×Tamuz-2granted the highest yield;19.875 and 19.724 g plant-1 respectively. Tamuz-2 recorded the highest positive General Combining Ability values (2.331and 2.479) for grain yield plant-1 at Kanipanka and Qlyasan, respectively. The cross Maroof ×Tamuz-2 showed the maximum positive Specific Combining Ability effect values (3.034) for grain yield plant-1 at Kanipanka, while at Qlyasan the cross Aras×Sabr Beg record the maximum value with 1.743. Testers brought many variations in the expression of the trait grain yield plant-1 at Kanipanka and Qlyasan, respectively. At both locations, the ratio of σ2gca /σ2sca value was less than one (0.062 and 0.450) and the average degree of dominance value was more than one (4.005 and 1.490) which confirmed that non-additive gene effect was in control for the trait grain yield plant-1. The maximum desirable positive heterosis value (26.082) recorded by the crosses Maroof×Tamuz-2 at Kanipanka location, while at Qlyasan location the cross Aras×SabrBeg recorded the maximum desirable positive heterosis value (26.989) for grain yield plant-1.

Analysis of genetic effects on a complete diallel cross test of Pinus koraiensis

Thirty-four full-sib Pinus koraiensis families were used to evaluate and identify elite P. koraiensis material. Tree height (H) and diameter at breast height (dbh) were assessed. The results from variance analyses showed that familial variance sources for different traits in different growth years were extremely significantly different. The average phenotypic variation coefficients of H, dhb and volume (V) among families in different growth years ranged from 7.57 to 15.70, from 10.37 to 12.89 and from 24.44 to 28.13%, respectively. The family heritabilities of all traits ranged from 0.910 to 0.990, which are high values. A significant and positive correlation was observed among all traits, with values ranging from 0.43 to 0.99. According to the analyses of general and special combining ability, female parents F4 and F2 and male parents M7 and M13 had high levels of general combining ability for all three traits evaluated. Families PK05 (F9 × M14) and PK06 (F2 × M14) showed the highest and the lowest specific combining ability values in all traits evaluated. Using the comprehensive multiple-traits method to evaluate the families by traits in the 18th growth year at the rate of < 10%, we selected families PK40, PK05 and PK22 as elite families; the genetic gains for these families in H, dbh and V were 14.43, 11.29 and 24.72%, respectively. This study provides materials and basic theoretical knowledge that can be used to improve seed orchards and develop special hybrid seed orchards.

Combining ability of six s7 generation of corn hybrid parents from half dialel crossesof Maize in a Half Diallel Crosses

Combining ability is the genotype's ability to pass on the desired character to the offspring. Combining ability information is needed to determine the crossed pairs in the formation of hybrid varieties. The purpose of this study was to obtain information on the combining ability value of six S7 generation of inbreed maize. The experiment was conducted in September 2015 until January 2016, at Medan Baru Experimental Station of Faculty of Agriculture, at Kandang Limun village, Muara Bangkahulu Sub-district, Bengkulu City. The experiment was prepared in a Randomized Block Design (RCBD) with 15 corn hybrid treatments including: G1XG3, G1XG6, G3XG6, G1XG7, G3XG7, G6XG7, G1XG8, G3XG8, G6XG8, G7XG8, G1XG9, G3XG9, G6XG9, G7XG9 and G8xG9. Each experimental unit was repeated three times obtaining 45 experimental plots. Estimation of general combining ability (GCA) value and specific combining ability (SCA) of each inbreed strain were conducted with Griffing model IV method. The results showed that genotype G1 and G3 had positive GCA values for all characters except plant height. The G7XG1 cross combination showed a positive SCA on all characters even higher in plant height and stem diameter. The G8XG6 cross combination showed high SCA values for leaf number characters, weight of husk-less cob, number of seeds per seed-line, weight of grain per ear, and grain yield per plot.Keywords: Hybrid, corn, GCA and SCA

Genetic parameters and genotype by environment interaction of Eucalyptus grandis populations used in intraspecific hybrid production in South Africa

In South Africa, Eucalyptus grandis is an important species due to its fast growth and general suitability of its timber for a range of products. However, E. grandis is susceptible to fungal diseases such as Crysoporthe austroafricana and Coniothyrium sp. cankers in the subtropical region of Zululand and is therefore mainly planted as a parental species in a hybrid combination with E. urophylla in this region. The current strategy is to maintain large breeding populations of both parental species in order to provide improved elite selections for hybrid crosses. In order to develop the best interspecific hybrid breeding strategy for E. grandis, it is important to first determine estimates of genetic parameters of the pure species parents. Estimating the genotype by environment interaction (G×E) is also necessary in proposing the basis for setting up breeding populations and selecting environmentally stable genotypes. With this in mind, two E. grandis full-sib progeny trials were planted in Zululand and one in the KwaZulu-Natal Midlands region. The aims of this study were firstly to determine the magnitude of G×E of E. grandis across the three sites; secondly, to estimate the genetic parameters for growth of the E. grandis parents selected for intraspecific crosses; and lastly, to identify the best parents to use for intra- and interspecific crosses in future hybrid breeding programmes. Results of our study indicated that G×E would be practically negligible for growth in Zululand and one group of elite parents can be used for hybrid crosses in this region. In general, growth traits were under low to moderate genetic control, and the variation in additive genetics enabled us to identify E. grandis parents that could be utilised for intraspecific crosses and deliver progeny with genetic gains of 28.4%. Our study also highlighted that a relatively large portion of the genetic variation was explained by dominance genetic variation and a strategy to capture this non-additive variation needs investigation. Although our study achieved the stated aims, it must be kept in mind that E. grandis is mainly used as a hybrid parent with E. urophylla in Zululand. A study to investigate whether the parents with good general combining ability values from our study are also good general combiners in interspecific hybrid combinations with E. urophylla needs to be conducted.

Quantitative analysis of gene actions controlling root length under water stress in spring wheat (Triticum aestivum L.) genotypes

Understanding the genetic control of agronomic traits is important in designing crop improvement programs. Study was conducted to analyse the genetic control of root length under water stress. A full diallel cross of four spring wheat lines, along with their F1 progenies was evaluated under –0.82 MPa water stress in a hydroponic culture. Analysis of variance showed highly significant (P &lt; 0.01) difference among the parental lines and their F1 progenies. Genotypes Santa Elena, Colotana 296–52 and Pato showed comparable longer roots whereas Tincurrin grew significantly (P &lt; 0.05) shorter roots. Genotypes with long roots were found to have more dominant genes than those with shorter roots. Both general and specific combining abilities were highly significant (P &lt; 0.01) indicating the importance of additive and dominant gene effects in the control of root length under water stress. Genotype Santa Elena was found to be the best general combiner whereas the specific cross Santa Elena × Pato was the best hybrid. Moderate narrow-sense heritability (38%) was observed indicating the possibility of improving root length under water stress. The highly significant specific combining ability value (dominant genetic control) suggests that genotypes with more dominant genes should be selected as parents for hybridisation and the hybrid wheat approach might be helpful in improving water stress resistance.

Inheritance of nitrogen use efficiency in inbred progenies of tropical maize based on multivariate diallel analysis.

The objective of our study was to characterize and determine the patterns of genetic control in relation to tolerance and efficiency of nitrogen use by means of a complete diallel cross involving contrasting inbred progenies of tropical maize based on a univariate approach within the perspective of a multivariate mixed model. Eleven progenies, previously classified regarding the tolerance and responsiveness to nitrogen, were crossed in a complete diallel cross. Fifty-five hybrids were obtained. The hybrids and the progenies were evaluated at two different nitrogen levels, in two locations. The grain yield was measured as well as its yield components. The heritability values between the higher and lower nitrogen input environment did not differ among themselves. It was observed that the general combining ability values were similar for both approaches univariate and multivariate, when it was analyzed within each location and nitrogen level. The estimate of variance of the specific combining ability was higher than general combining ability estimate and the ratio between them was 0.54. The univariate and multivariate approaches are equivalent in experiments with good precision and high heritability. The nonadditive genetic effects exhibit greater quantities than the additive genetic effects for the genetic control of nitrogen use efficiency.

Exploiting Grain‐Filling Rate and Effective Grain‐Filling Duration to Improve Grain Yield of Early‐Maturing Maize

ABSTRACTEarly‐maturing maize (Zea mays L.) genotypes yield 15 to 30% less than late‐maturing genotypes. One strategy for improving grain yield in the early‐maturing group involves assessment of grain‐filling traits as secondary traits for selection for high grain yield. In this study, we investigated the possibility of using grain‐filling rate and duration for improving grain yield in early‐maturing tropical maize. Forty‐four hybrids generated using North Carolina design II were evaluated at CIMMYT‐Zimbabwe during the 2011/2012 season under irrigated and nonirrigated environments. Although grain‐filling rate and effective grain‐filling duration were negatively correlated, several hybrids were distinctly above the trend line. The earliest‐maturing hybrid took 127 d to reach physiological maturity and produced grain yields comparable to those of the medium‐maturing genotypes (7 t ha−1). It had a high grain‐filling rate of 2.40 g per plant d−1 (18% higher than those of the low‐yielding hybrids) and a relatively longer effective grain‐filling duration. Grain‐filling rate and effective grain‐filling duration had high coefficients of genetic determination, positive correlations with grain yield, low error terms, and low genotype × environment interactions, making them appropriate selection traits for improved grain yield. The study shows that it is possible to develop high‐yielding early‐ to medium‐maturing maize hybrids based on favorable combining ability values for grain‐filling rate and duration.

Gene effect, combining ability and heterosis in sunflower morphophysiological traits

SUMMARY Four interspecies populations, originating from three annual ( H. debilis, H. praecox, H. deserticola ) and one perennial ( H. resinosus ) wild species, were used to produce 13 new ( cms ) inbred lines with cytoplasmic male sterility, three Rf restorer lines with good general combining ability used as testers and their F 1 hybrids. A two-year trial with three replicates was set up using the line × tester method. The inbred A-lines, Rf -testers and F 1 hybrids differed significantly in the mean values for both studied traits. The mode of inheritance for leaf area was dominance and superdominance of the better parent and for plant height it was superdominance of the better parent. Highly significant positive values of general combining ability for both traits were found in inbred lines NS-G-7, NS-G-8, NS-G-9. The greatest highly significant positive specific combining ability value was found in NS-G-6 × RUS-Rf-OL-168 for the total leaf area per plant and in NS-G-6 × RHA-N-49 for plant height. The non-additive gene effect had greater influence on both traits. A significant heterotic effect was found for both traits in relation to the parental average so as in relation to the better parent.

Inheritance of resistance to root-lesion nematode (Pratylenchus thornei) in wheat landraces and cultivars from the West Asia and North Africa (WANA) region

The root-lesion nematode Pratylenchus thornei causes substantial loss to bread wheat production in the northern grain region of Australia and other parts of the world. West Asia and North Africa (WANA) wheat accessions with partial resistance to P. thornei were analysed for mode of inheritance in a half-diallel crossing design of F1 hybrids (10 parents) and F2 populations (7 parents). General combining ability was more important than specific combining ability as indicated by components of variance ratios of 0.93 and 0.95 in diallel ANOVA of the F1 and F2 generations, respectively. General combining ability values of the ‘resistant’ parents were predictive of the mean nematode numbers of their progeny in crosses with the susceptible Australian cv. Janz at the F1 (R2 = 0.86, P &lt; 0.001, 8 crosses), F2 (R2 = 0.83, P &lt; 0.001, 9 populations) and F∞ (R2 = 0.71, P &lt; 0.05, 5 doubled-haploid populations). The F2 and F∞ populations showed relatively continuous distributions. Heritability was 0.68 for F2 populations in the half-diallel of resistant parents and 0.82–0.92 for 5 ‘resistant’ parent/Janz doubled-haploid populations (narrow-sense heritability on a line mean basis). The results indicate polygenic inheritance of P. thornei resistance with a minimum of from 2 to 6 genes involved in individual F∞ populations of 5 resistant parents crossed with Janz. Morocco 426 and Iraq 43 appear to be the best of the parents tested for breeding for resistance to P. thornei. None of the P. thornei-resistant WANA accessions was resistant to Pratylenchus neglectus.

Capacidade combinatória entre híbridos simples de milho em dialelo circulante

Onze híbridos comerciais de milho (AS 1550, DKB 214, DKB 215, DKB 330, Dow 2B150, Dow 8460, P 30F33, P 30F53, P 30P70, Penta e Premium Flex) foram intercruzados, obtendo-se 44 híbridos duplos, segundo um dialelo circulante com p=11 (onze genitores) e s=8 (intercruzados 8 a 8), avaliado em delineamento em blocos casualizados com três repetições. Foram conduzidos dois experimentos na Região Centro-sul do Paraná, nos municípios de Guarapuava e Goioxim. Os dados referentes à produção de grãos, altura média de planta e altura média de inserção de espiga foram submetidos à análise dialélica. Houve diferenças significativas entre os locais e entre os híbridos do dialelo para as três características avaliadas. Também houve efeito significativo da interação locais x híbridos do dialelo para a produção de grãos. Houve diferenças significativas para a capacidade geral de combinação (CGC) em todas as características e para a capacidade específica de combinação (CEC) apenas na produção de grãos. Destacaram-se por sua CGC os híbridos Penta, P 30F53 e Dow 8460 na produção de grãos, o híbrido AS 1550 quanto á menor altura de planta e de inserção da espiga. A melhor combinação híbrida para a produtividade foi Penta x P 30F53, por apresentar a maior média, elevada CEC e ambos os genitores terem as maiores estimativas de CGC. O genitor P 30F53 participou de três dos quatro híbridos duplos mais produtivos. É possível a obtenção de novas populações a partir de cultivares comerciais que se destacaram por sua CGC, e que, nos cruzamentos em que participaram, houve, também, estimativas favoráveis da CEC.

Genetic effects on carcass-quality traits in hybrid striped bass (Morone chrysops ? � Morone saxatilis ?)

A 10 × 10 factorial mating design was used to examine the genetic effects on various carcass-quality traits in hybrid striped bass (Morone chrysops♀×Morone saxatilis♂). A total of 448 offspring were raised in a ‘common-garden’ environment and carcass-quality traits were assessed at 389 days post fertilization; parentage of each fish was inferred from genotypes at 5–10 nuclear-encoded microsatellites. There was a significant effect of dam and sire on body weight and fillet weight and a significant effect of dam on viscera weight and condition factor. When carcass-quality traits were standardized to body weight, there was a significant effect of dam, sire and dam × sire interaction on viscera percentage (proportion of viscera weight to body weight). Phenotypic correlations between body weight and non-standardized carcass-quality traits were high (rp=0.80–0.92), whereas phenotypic correlations between body weight and standardized carcass-quality traits were low (rp=0.13–0.19). Genetic correlations between body weight and fillet weight (dams and sires), and body weight and viscera weight (dams only) were significant and positive, while the genetic correlations between body weight and viscera percentage (dams and sires) were significant and negative. Significant general combining ability values for favourable carcass-quality traits in the same breeder (dam or sire) occurred only in one or two of 20 (dams and sires) used in this study, suggesting that simultaneous improvement in multiple traits in hybrid striped bass may require evaluation of large numbers of candidate breeders. The effect of sex on body weight and all non-standardized carcass-quality traits was significant and appeared to be due to faster growth in females. These results indicate that selection for faster growth of hybrid striped bass would lead to a correlated increase in fillet weight and viscera weight but not necessarily to an increase in the proportion of fillet and waste product generated. The significant dam, sire and dam × sire interaction effects on viscera percentage and the negative genetic correlations between body weight and viscera percentage indicate that selection for reduced proportion of viscera relative to body weight might be feasible.