Combining ability and gene action for maturity and agronomic traits in different heterotic groups of maize inbred lines and their diallel crosses

Combining ability information is necessary for selection of suitable advanced lines for hybridization and identification of promising hybrids for development of improved varieties. A number of 14 maize (Zea mays L.) inbred lines and 91 related crosses were evaluated over two years, 2008 and 2009, in a temperate-zone of Iran. The objectives of the study were to identify the best general and specific combiners, heterosis and type of gene actions responsible for agronomic traits. Except for grain yield and growing degree day to milky, significant general (GCA) and specific (SCA) combining ability were observed for all traits. The Baker ratio for plant height (0.15), ear height (0.26), growing degree day to milky stage (0.04), and grain yield (0.002) showed the predominance of non-additive gene effects in the expression of these traits. The heterosis observed for grain yield, grain number, pollination period, ear and plant height was considerably higher than that observed for other traits. The correlations (r) of F₁ means and SCA effects were positive and significantly higher than that of r (F₁, mid-parents) and r (F₁, heterosis) for all the traits except cob percent, growing degree days to silking, and physiological maturity. MO17, K3547/5, and K3615/2 had negative GCA effects for growing degree day to milky stage and maturity. Among hybrids, MO17 × K3653/2, B73 × K3651/2, and K3545/6 × K3493/1 with positive SCAs for pollination period and grain yield had also negative SCA effects for degree day to silking and milky stages. Therefore, the use of these inbred lines and hybrids increases the response to selection for increasing grain yield and early maturity in maize.     

Combining ability for femaleness and yield in single and 3-way crosses of pickling cucumbers intended for once-over harvest

Summary Single and 3-way cross hybrids derived from 13 parental lines of pickling cucumber were used to estimate general and specific combining ability for femaleness and yield. Parental lines 551F, 368G, 581H, and 5802A exhibited the highest general combining ability effects in both single and 3-way crosses for total yield and marketable yield. Additive effects of genes were found to be relatively more important than nonadditive effects for both femaleness and yield. Cucumber breeders might develop high yielding cultivars based on high general combining ability for yield in parental arrays; moreover, the general performance of the parental lines in single crosses could be used to predict high yielding 3-way hybrid crosses.     

Combining ability and heterosis of elite drought-tolerant maize inbred lines evaluated in diverse environments of lowland tropics

Estimates of combining abilities and heterosis of inbred lines are imperative for selection of suitable parents of maize hybrids. This study examined the combining ability of 24 drought-tolerant maize inbred lines, 12 each from International Centre for Maize and Wheat Improvement (CIMMYT) and International Institute of Tropical Agriculture (IITA). The lines were allotted into six groups each comprising four lines. The four lines in one group were used as females and crossed to the four lines in another group as males in six different sets using a North Carolina Design II mating scheme to generate 96 hybrids. The hybrids were evaluated together with four checks across six environments in the rainforest and savannah agro-ecologies of Nigeria between 2011 and 2012. The parental inbred lines were also evaluated in separate trial in each location. Significant hybrids × environment interaction was observed for grain yield and other measured traits. GCA effects accounted for 83.3% of the variation for grain yield at Bagauda, 78.1% at Saminaka, and 77.7% at Ikenne. GCA also contributed 91.1 and 80.0% to the variation observed for plant height and ear aspect, respectively, across the environments. Significant SCA × environment interaction detected for grain yield suggests that hybrids were not stable across test environments. Prediction of grain yield in hybrids using midparent values resulted in a R ² value of 0.13. Midparent heterosis for grain yield varied from 80 to 411%, with the top 36 hybrids recording >200%. Four CIMMYT (EXL02, EXL06, EXL04 and EXL16) and three IITA (ADL33, ADL41, and ADL32) inbred lines had positive and significant GCA effects for grain yield across environments. The novel alleles present in the CIMMYT lines will improve the adapted IITA germplasm in a new population for extracting new set of more productive inbred lines for developing adapted high yielding drought-tolerant maize hybrids.     

Combining ability analysis and correlation between breeding values in true potato seed

True potato seed (TPS) requires the selection of appropriate parents for developing hybrid offspring. Parents for routine crossing schemes need to be selected according to their combining ability. Hierarchical and factorial mating designs provide a mean values to assess the general combining ability (GCA) of clones included in crossing schemes. Furthermore, specific combining ability (SCA) may be investigated using the factorial mating design. The aim of this research was to determine the combining ability of clones included in early and intermediate TPS breeding populations developed by the Centro Internacional de la Papa (CIP). Likewise, correlations between breeding values (or additive genetic correlation, p_A) were calculated. Two hierarchical mating designs (in both the early and intermediate populations) and one factorial mating design (in the intermediate population) were evaluated in two contrasting Peruvian locations (La Molina ‐ coastal desert, and San Ramon, warm humid tropics). Plant and tuber characteristics were recorded in these experiments. Significant GCA was observed for tuber yield in all experiments. The male's p_A between plant vigour after transplanting and tuber yield was significant, thereby suggesting that offspring with early vigorous growth are high yielding. Plant vigour was also correlated with tuber set, but only among the breeding value of female parents, which suggests that high tuber yield could be achieved because offspring with early, vigorous growth have many tubers. High tuber yielding hybrids can be obtained by choosing parents with significant GCA, whose tuber yield can also be further enhanced if the crosses have a significant SCA.     

Combining ability of common bean (Phaseolus vulgaris) genotypes for root traits across diverse environments

Root system architecture is important for common bean (Phaseolus vulgaris) adaptability to diverse environments. Beans employ complex adaptive root mechanisms for coping with multiple stresses in production environments. Understanding genetic control of root traits is central to improvement of common bean for adaptation to marginal environments. The objectives of this study were to (i) determine combining ability of root and agronomic traits and (ii) estimate the heritability and genetic correlation of root and agronomic traits in common bean. Four bean lines with superior root traits were crossed with four locally adapted varieties in a North Carolina II mating scheme to generate 16 crosses. The 16 F₁s were selfed and advanced to F₂ generation. Eight parents and their F₂ progenies were evaluated in an alpha-Lattice design with two replications. General and specific combing ability mean squares were significant (p ≤ .05) for all traits measured. General predictability ratios ranged from .47 to .68 across locations suggesting that both additive and non-additive gene action modulate root traits and seed yield. Positive and significant (p ≤ .05) phenotypic and genetic correlations revealed significant association between root traits and yield. Moderate to high heritability estimates of between .43 and .67 were realized. Such estimates point to possible deployment of a successful selection programme. Genotype AFR398 displayed significant positive GCA effects among its crosses for both root and agronomic traits hence a potential candidate genotype for inclusion in a bean genetic improvement programme for marginal environments.     

RFLP diversity within and between major groups of barley in Europe

Restriction fragment length polymorphism (RFLP) diversity has been determined and analyzed as expressed by 33 single‐ or low‐copy clone/ enzyme combinations at 32 loci distributed over all chromosomes of the barley genome within a sample of 223 European barley accessions comprised of pure line (single‐head progenies) genotypes. The accessions have been selected to include landraces and widely grown cultivars derived from crossbreeding during the 20th century in North‐, West‐ and Central European countries. Genetic diversity obtained from 83 alleles across all accessions is characterized by the diversity index H = 0.385. The diversity indices determined for landraces and cultivars were almost equal, with the difference between spring (H = 0.260) and winter (H = 0.415) barley approaching statistical significance, while comparisons of other groupings only revealed statistically insignificant trends. A more detailed analysis based on differences in allele frequency distributions at each locus (clone/enzyme combinations resp.) revealed very clear differences related to the existence, continuity and dynamics of changes in group‐specific RFLP profiles. With the majority (69%) of RFLP alleles at 23 out of 32 loci on all barley chromosomes involved, contributions from chromosomes 1H, 3H, 4H and 5H seem to be of special importance. Differences in the overall average of abundance indicate higher levels of genetic diversity within both groups of winter barley compared with both groups of spring barley, from which the most frequent alleles at 15 (2‐rowed spring barley) and 17 (6‐rowed spring barley) RFLP loci approach fixation. The results of this study are discussed in relation to the history of barley cultivation and barley breeding in Europe, and possible explanations for group‐specific differences in the RFLP profiles of landraces and cultivars as well as for the high levels of (nearly) fixed alleles of both subsets of spring barley, and with respect to progress in barley breeding that it has been possible to obtain within the rather narrow RFLP profiles.     

Differences in reciprocal crosses of maize inbred lines diverse for protein content

Summary Forty-two crosses and their reciprocals in maize (Zea mays L.) involving inbred lines highly diverse for protein content were evaluated in four environments. Data were recorded on crude protein content of grain, protein yield, grain yield, 1000 kernel weight, dry matter content of ear at harves,, days to 50% slking, plant height, ear height, and early vigor. No significant variation due to reciprocal differences was observed for protein content and early vigor. For all other traits the variance component due to reciprocal x environment interactions was significant while the variance component due to reciprocal differences was significant only for kernel weight, dry matter content of ear, plant height, and ear height. The variance components due to nuclear differences and their interactions with environments were always highly significant and larger than the components due to reciprocal differences and reciprocal x environment interactions. The instability and low magnitude of reciprocal differences indicated that it might be difficult to exploit them commercially. However, seeing the presence of reciprocal differences for most of the traits studied, the evaluation of breeding materials for these differences seems to be important.The research work was supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 142.     

Combining ability estimates for yield and fibre quality traits in 4 × 13 line × tester crosses of Gossypium hirsutum

The aim of this study was to estimate the general combining ability of the parents and specific combining ability of hybrids considered for the development of high yielding and better quality cultivars. Seventeen genotypes and 52 F₁ hybrids obtained by crossing 4 lines and 13 testers in line × tester mating system during 2003 were sown in randomized complete block design in 2004. Line × Tester analysis revealed significant GCA and SCA effects for all the traits except fibre elongation. Preponderance of non-additive gene action was obtained for seed cotton yield per␣plant and majority of its component traits including fibre traits. Among the parents: PIL-8 for days to 50% flowering, CCH-526612 for boll weight, CITH-77 for number of open bolls per plant and CNH-36 for seed cotton yield per plant were detected with higher general combining ability. Parent, CCH-526612 for 2.5% span length, fibre strength and fibre elongation and AKH-9618 for micronaire value, fibre strength and fibre elongation were good combiners for fibre quality traits. The F₁s achieved high seed cotton yield by producing more number of open bolls. The high yielding hybrids with acceptable fibre quality traits were: CISV-24 × LH-1995, H-1242 × PIL-8 and RS-2283 × SGNR-2 deducted with significant SCA effects for seed cotton yield and fibre characteristics; 2.5% span length and fibre strength. These cross combinations involved at least one parent with high or average GCA effect for a particular trait.     

Combining ability of seed vigor and seed yield in soybean

Studies have shown no consensus in relationships between seed yield and vigor in soybean [Glycine max (L.) Merrill]. The lack of information regarding the inheritance of seed vigor prompted this study to determine the types of gene action and combining ability estimates for seed vigor and its related traits. Five high and six low seed vigor soybean genotypes were crossed in a diallel, and selfed to produce 55 F₂ progenies, which were examined, along with the parents, for seed vigor, yield, and seed weight. Significant genotype and environment effects were found for seed vigor and yield. General combining ability (GCA) effects for seed vigor and seed yield were significant (p≤ 0.01) and larger than specific combining ability (SCA) effects. Significant GCA and SCA effects were found for seed weight, indicating that both additive and non additive genetic effects were involved in conditioning seed weight. The ratios of mean square, 2GCA / (2GCA+SCA), were 0.96 for seed vigor and 0.93 for seed yield. These ratios indicated that additive gene effects were more important than non additive gene effects for seed vigor and seed yield in these crosses. Mean seed vigor(83.8%), as determined by accelerated aging germination, and mean seed yield (2,155 kg ha^-1)in high vigor × high vigor crosses were higher than the high vigor × low vigor and low vigor × low vigor crosses. Mean percent accelerated aging germination rates in F₂ populations from diallel crosses were significantly related to mid-parent seed vigor(r² = 0.52^**) and midparent seed size (r² = 0.31^**). These results indicated that levels of seed vigor can be improved through breeding, while maintaining high yields because of the predominance of GCA effects in both seed vigor and seed yield. This revised version was published online in July 2006 with corrections to the Cover Date.     

同源姊妹种与其双亲的配合力测定

被测的两个同源自交系和相配的两个姊妹种．系与系之间、系与姊妹种之间、姊妹种之间（正反交）产量差异都不显著、而产量之间的差异主要是由于测验种之间的差异造成的。配合力测定结果．两个同源自交系和两个姊妹种中,系与系之间,系与姊妹种之间,两个姊妹种之间一般配合力差异不显著，说明利用配合力差异不显著的姊妹种替代自交系是可以作为杂交亲本生产种子的。     

Combining ability for yield and plant phenology in plantain-derived populations

Genetic enhancement of Musa spp. has aimed at producing hybrids with high yield, short stature, fast crop cycling, and disease resistance through interspecific and interploidy crosses. Progeny testing for parental selection has seldom been carried out in Musa and little is known on combining ability and heterosis in this species. A 5 × 5 factorial mating design was used to estimate components of phenotypic variance in 4 x-2 x hybrid populations and to determine the combining ability of their progenitors for yield and associated traits. General combining ability was much greater than specific combining ability for these traits, and, therefore, only little recombinative heterosis could be expected upon crossing. Thus, the 4 x-2 x breeding scheme should aim to accumulate favourable alleles in 4 x and 2 x clones through recurrent selection. Such clones could be used per se or in crosses aimed at restoring the seedlessness character in the progeny due to female sterility in a triploid background. This revised version was published online in August 2006 with corrections to the Cover Date.     

Forage quality of genetically diverse alfalfa germplasms at four phenological growth stages

Summary Forage quality of various alfalfa (Medicago sativa L.) cultivars has been determined under different environmental conditions, and numerous trials with alfalfa have documented an inverse relationship between forage quality and maturity. Little information is available, however, regarding the comparative forage quality of the germplasm sources from which most USA cultivars were developed. We compared forage quality of these germplasm sources at four phenological stages under disease- and insect-free conditions in a greenhouse. Germplasm sources (cultivars) tested were: Indian (Sirsa #9), African (African), Peruvian (Hairy Peruvian), Flemish (DuPuits), Turkistan (Lahontan), Chilean (Kansas Common), M. varia (Grimm), and Ladak (Ladak). Four harvests were taken and forage was separated into four phenological stages: vegetative, early bud (1–3 buds-per-stem), late bud (>3 buds-per-stem), and bloom. The germplasm source X phenological stage interaction was significant for crude protein (CP) and in vitro digestible dry matter (IVDDM) concentrations. M. varia showed the least decline in IVDDM and CP with increasing maturity. M. varia had higher IVDDM than did African and Indian at late bud and bloom stages. Indian and Flemish had higher CP than did Turkistan and Peruvian at late bud and bloom stages. Alfalfa germplasm sources differ in forage quality when comparisions are made within similar stages of phenological development.Joint contribution of the Dept. of Agronomy and USDA-ARS, Kansas Agricultural Experiment Station, Manhattan, KS 66506, USA. Contribution no. 90-475-J.     

Combining ability analysis for harvest index in winter wheat

Summary Cereal breeders have used harvest index (HI) as a selection criterion in segregating generations to identify physiologically superior lines with improved partitioning of total assimilate into grain. Information on combining ability for HI of the hard red winter wheat (Triticum aestivum L.) cultivars of the Southern Great Plains is not available. A study was undertaken to examine HI of seven genetically diverse winter wheat parents, evaluate their general combining ability (GCA) and specific combining ability (SCA) effects, and study correlations of HI with several agronomic traits. The seven parents were crossed in a half-diallel mating design to produce 21 crosses. The F₁'s, their F₂ progenies, and the parents were evaluated in replicated field tests at Stillwater and at Lahoma, OK. The combining ability analysis was performed using Griffing's Method 4, Model 1. The results showed significant variation among parents for HI. The GCA and the SCA effects were mostly inconsistent between generations and between environments. However, parents with consistently high HI and positive GCA estimates were identified. The progeny with high HI mostly resulted from parents with high GCA estimates. The correlations between HI and agronomic traits indicated that improvement in HI should also result in high grain yield, early maturity, and short plant height.     

Agronomic performance of crosses between Nordic and exotic barleys

Exotic germplasm may be useful for the improvement of agronomic performance of barley breeding material. This study was conducted in order 1) to evaluate if it is possible to improve performance of Nordic barley breeding material by utilizing exotic germplasm sources (unadapted landraces and H. spontaneum), 2) to evaluate incorporation of exotic germplasm into a genetic base widely adapted to the agro-ecological conditions of the extreme Scandinavian north as well as to the base adapted to the conditions of the south of this geographical region, and 3) to evaluate whether an index composed of several traits corresponded to 'breeder's phenotypic evaluation' of the progenies. Earliness, straw length, number of ears/plant, yield/plant, seed shattering, persistence of awns and an index computed from these traits were studied in Swedish and Finnish 4-way crosses along with their adapted parents. Most of the crosses headed earlier than their adapted parents and none of the crosses outyielded the adapted parents. The most favorable frequency distributions for the index were found in the crosses with only cultivated barleys as parents. Transgressive segregates were also found in progenies with H. spontaneum parents. Incorporation of exotic barleys was most successful into the local genetic base. Comparisons between indices and breeder's phenotypic evaluation suggested reconsideration of evaluation methods early in parent development.     

Combining ability for yield and fibre characteristics in Tanzanian cotton germplasm

In Tanzania, cotton is of great economical importance, representing a large percentage of agricultural exports, but yield and lint quality is still relatively poor. The aim of this study was to identify parents to improve boll and lint yield and quality. Parents and F1 progeny of a 7 × 7 diallel were evaluated in four different environments. Results indicated significant variation for especially yield components, yield, ginning outturn and fibre quality. Parents with high and positive GCA like NTA 93-21, Delcot 344, Auburn 56 and MZ561 and combinations with high and positive SCA for the characteristics were identified. Additive genetic effects were seen for most of the characteristics, except for fibre strength at one locality. Parents with high GCA effects for certain characteristics produced combinations with high SCA effects for the same characteristics. This study indicated that there is enough genetic variability for boll and lint yield and quality for effective selection, and good parents that can be included in the breeding programme.     

玉米自交系KA105和91227的配合力分析

用陕A群自交系KA105、91227与甘肃省自育NSS群的14个自交系进行配合力测定,结果表明,KA105与各自交系单株产量的一般配合力(GCA)总体比较高,91227与各自交系单株产量的特殊配合力(SCA)总体比较高,单株产量总配合力(TCA)效应值较高的组合依次为KA105×1802、KA105×F5001、KA105×F0601和91227×1802。各性状的特殊配合力(SCA)的相关性分析表明,单株产量与秃尖长呈负相关,与其他性状均呈正相关,其中与穗位高、出籽率呈极显著正相关。在自交系选系中株高、穗长、出籽率、轴粗、雄穗分枝、穗行数、百粒重和穗粗可以早代进行选择,单株产量、穗位高和行粒数可在高代进行选择。     

Combining ability and heritability of soybean resistance to groundnut leaf miner

Groundnut leaf miner (GLM) (Aproaerema modicella) (Deventer) is one of the most destructive pests of soybean and groundnuts. In this study, the mode of inheritance, general combining ability (GCA), specific combining ability (SCA) effects, maternal effects of resistance to GLM and grain yield ha^?1 were determined. Thirteen soybean parental genotypes and 81 F₂ populations were evaluated for resistance to GLM in a 5?×?19 alpha lattice diallel design with two replications under natural GLM infestation in northern (Arua) and eastern (Iki-iki) Uganda during September to December 2016 rainy season. Highly significant differences were observed among parental genotypes and F₂ populations for GLM incidence, severity, and grain yield. The estimates of GCA effects were significant for GLM incidence and severity scores but not for the number of larvae per plant and grain yield ha^?1. SCA effects were non-significant for all the studied traits, suggesting that GCA effects were the major component responsible for soybean resistance to GLM with additive gene effects being more important for these traits. Baker’s ratio ranged from 0.44-1.0 for most of resistant traits except number of larvae per plant and grain yield ha^?1. The results indicated also that cultivars Maksoy1 N, PI615437, PI578457A and NIIGC4.1-2 were good combiners against GLM incidence and severity. Parent PI615437 was a good combiner for grain yield and Maksoy1 N?×?PI615437 was a superior cross for grain yield and against GLM incidence. There were no maternal effects for the inheritance of resistance to GLM. The study provides a basis for understanding patterns of inheritance of soybean resistance to groundnut leaf miner for an efficient breeding program.     

Pollen tube growth in crosses between Porteresia coarctata and Oryza sativa

Summary Comparative study with fluorescence microscopy revealed that the pollen tubes of the self-pollinated rice variety BR-9 reached the ovary within 75 min after pollination. In P. coarctata it took 150 min. In the cross between P. coarctata and BR-9, pollen tubes reached the ovary in 165 min but seed setting was not observed. In the cross between BR-9 and P. coarctata, small and deformed pollen tubes were formed and they failed to grow through the stylodium.     

Combining ability and correlations for yield components in early generations of potato breeding

A partial diallel set of crosses was made between 14 potato cultivars chosen for their fertility, from those included in a potato breeding programme at the NEIKER – Basque Institute for Agricultural Research. The progeny were grown in completely randomized trials from 1997 to 1999. Performance for yield, tuber number and average tuber weight was analysed in seedling and two clonal generations. Variance estimates due to both general combining ability (GCA) and specific combining ability (SCA) were significant in all generations for all traits under study. However, SCA was more important than GCA in almost all cases. Correlation coefficients among characters, generations, GCA and SCA effects were examined. For tuber yield no relation was obtained between generations; however, average tuber weight and yield were positively associated in all generations. The results indicate that appropriate selection criteria depend strongly on the particular cross. The implication for a breeding strategy are discussed.     

Combining ability of common bean parents in different seasons,locations and generations

The objectives of this study were to obtain information about genetic parameters of a partial diallel in common bean, as well as to evaluate the effects of growing seasons, locations and generations in these estimates in order to define the best strategies for the use of diallel analysis as methodology of selection of parents and populations in common bean breeding. Twelve parents were crossed in a partial diallel scheme (5?×?7), and the F₁ and F₂ generations were evaluated in four experiments (I, II, III, and IV). The effects of seasons were determined in the Experiments I and II, in which the F₁ generation was evaluated in two distinct growing seasons. To quantify the effect of locations, we used Experiments III and IV, in which the F₂ generation was evaluated in the same season, but at different locations, and to quantify the effect of generations, the experiments II (generation F₁) and III (F₂ generation) were evaluated in the same season and location. As for grain yield the genetic control varied according to the environment. An effect of interaction on the genetic parameters of the diallel was observed for generation, whereas for grain yield, effects of season and location were observed. For plant architecture, parental combining ability should therefore be estimated using the F₁ generation, while for grain yield, both the F₁ and F₂ can be used. The recombination between the best hybrids is a promising strategy for extraction of superior black bean lines.