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Geraniums (Pelargonium spp.) are ornamental plants that are widely popular because of their abundant flowering, color variability, different flower patterns, and ease of cultivation. Genetic breeding of this species aims to reduce the plant size and flower color. The objective of this study was to carry out morphoagronomic characterization of parents and F1 hybrids and to estimate the combined capacity and hybrid performance in the circulating diallel in F2 geranium (Pelargonium sp.). We obtained 18 and 275 plants from the F1 and F2 generations, respectively. Characterization of the parental genotypes and F1 and F2 hybrids was performed based on the descriptors for Pelargonium. Parents and F1 hybrids were grouped using the Tocher and UPGMA methods and diallel analyses in the F2 generation. The F1 hybrids G8, G11, and G17 exhibited color combinations suitable for commercialization and are promising for inclusion in breeding programs. The effects of general combining ability (GCA) and specific combining ability (SCA) were significant for these traits were also significant. The results showed the presence of both additive and non-additive genes. However, non-additive and dominant genes were predominant in most characteristics studied. Diallel analysis of the F2 hybrids revealed that the best hybrid combinations for reducing plant height were 14 × 11, 14 × 13, and 15 × 12. Therefore, the implementation and use of diallel analysis were efficient in selecting superior parental genotypes and producing hybrids with high yields. [ABSTRACT FROM AUTHOR]

Yield gains in crop plants, such as citron watermelon can be realised through combining ability tests and hybrid breeding. The objective of the study was to determine the combining ability and hybrid performance of citron watermelon genotypes for agronomic traits. Five contrasting and relatively high-yielding citron watermelon genotypes were crossed in a 5 × 5 half-diallel mating design and 10 F1 hybrids were developed. The 15 families (five parents and 10 F1 hybrids) were evaluated across two environments using a randomized complete block design with three replications. Data was collected on various agronomic traits and subjected to analysis of variance (ANOVA) and combining ability analysis. Significant (P < 0.001) genotype × environment interaction effects were observed for most assessed traits. General combining ability (GCA) and specific combining ability (SCA) effects were significant (P < 0.001) for most traits. Environment × GCA was non-significant, whereas Environment × SCA effects were significant (P < 0.001) for most traits. The ratios of GCA/SCA variances were less than unity for most traits, indicating non-additive gene action of the traits. Broad-sense heritability varied from low to moderate, implying variable selection response of the assessed traits among the F1 hybrids. The parental genotypes WWM16 with positive GCA effects for fruit and seed yields and WWM66, with positive GCA effects for the number of seeds per fruit and seed yield, were identified for hybrid breeding. The following F1 hybrids: WWM04 × WWM16, WWWM03 × WWM66 and WWM16 × WWM50 with positive SCA effects on total fruit yield per plant and marketable fruit yield per plant, and WWM04 × WWM50, WWM03 × WWM16 and WWM03 × WWM66 with positive SCA effects for number of seeds per fruit and total seed yield were identified. The study identified novel and best-performing F1 hybrids of citron watermelon for economic traits and are recommended for multi-environmental evaluations, variety registration and commercialization. [ABSTRACT FROM AUTHOR]

Quality Protein Maize (QPM) varieties are rich in lysine and tryptophan, but suffer reduced grain yield (GY) in West and Central Africa (WCA) due to low soil nitrogen (low-N) and intermittent drought stress (DS). Development of stress-tolerant QPM hybrids will enhance sustainable maize production and improve nutritional health in WCA. Knowledge of combining ability, gene action and heterotic grouping of QPM inbred lines are crucial to successful breeding strategies for the development of superior hybrids with enhanced nutritional values. The objectives of this study were to: (i) determine the combining ability for GY and yield-related traits among 13 newly developed QPM inbred lines, and (ii) assign the QPM inbred lines to distinct heterotic groups based on general combining ability effects of multiple traits under low-N and DS conditions. Seventy-eight single cross hybrids were generated through half-diallel mating of 13 QPM inbred lines and evaluated along with three commercial checks for GY and yield-related traits under the low-N and DS conditions. Significant general combining ability (GCA) and specific combining ability effects were obtained for GY and yield-related traits. Both additive and non-additive gene effects were involved in the inheritance of GY and other traits under low-N and DS conditions. However, the additive gene effect for GY was twice as large as non-additive gene effect. Three heterotic groups were each delineated under low-N and DS. Inbred lines, CRIZEQ-44 and CRIZEQ-77 belonging to different heterotic groups were identified as testers for the development of superior hybrids for low-N and DS environments. [ABSTRACT FROM AUTHOR]

Genetic advancement and gains in yield and related traits are dependent on the selection of best combiner parents and progenies under the prevailing growing conditions. This study was conducted to determine the combining ability effects of eight selected drought-tolerant groundnut parental lines and their F2 progenies under drought-stressed (DS) and non-stressed (NS) conditions to determine the gene actions involved in the inheritance of the studied traits and identify the best parents and progenies for further improvement of the crop for moisture stress tolerance. Experiments were conducted at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in India during 2020 cropping season. Data on some of the important physiological, yield and yield component traits were collected. The general combining ability (GCA) effects of parents were significant (P < 0.05) for all assessed traits under all testing conditions, except for PB under DS and NS conditions in the glasshouse. The specific combining ability (SCA) effects of progenies were significant (P < 0.05) for all traits, except for PH across all testing environments and PB under field conditions. The genotype ICGV 10178 was the best general combiner with positive contribution and significance to SCMR, PY, SHP, KY, TBM and HI and reduced SLA. Crosses ICGV 10178 × ICGV 11369, ICGV 10373 × ICGV 15083, ICGV 98412 × ICGV 15094 and ICGV 10178 × ICGV 98412 were the best specific combiners for enhanced pod yield and drought tolerance. The GCA was found predominant over the SCA effect for the inheritance of PY, KY and TBM. Higher GCA: SCA rations were recorded for PY and KY under both DS and NS conditions, and SCMR, SLA and TBM under DS condition suggesting the predominant role of additive genes conditioning the inheritance of these traits. Therefore, the above new progenies are useful populations for developing improved pure line groundnut varieties with high pod yield and drought tolerance. [ABSTRACT FROM AUTHOR]

An efficient hybrid breeding program defines and utilizes a few heterotic groups. Objectives of this study were to determine genetic diversity and alignment of South Africa maize inbred lines collection towards tropical and temperate testers. Forty-four maize inbred lines were genotyped with 56,110 single nucleotide polymorphism (SNP) markers. A total of 40 lines were crossed to two tropical and two temperate inbred line testers. Due to seed shortages, testcross hybrids containing 14 and 18 lines were used in 2014/2015 and 2015/2016 seasons, respectively. Genotypes and specific combining ability (SCA) effects of hybrids were significantly different (P < 0.05) for grain yield. There was a weak correlation between molecular genetic distances and both grain yield mean performance and SCA effects of hybrids, indicating that productivity of maize inbred lines could not be reliably determined based on molecular genetic distances. The SCA data classified these maize inbred lines into three heterotic groups with respect to both tropical and temperate testers. The study also indicated high level of diversity among the maize inbred lines, which was shown by both the dendogram and molecular genetic distances. The SNP marker data classified the inbred lines into 11 clusters that could be simplified into three major groups of normal maize endosperm and two groups of quality protein maize endosperm types. However, the SNP data indicated that maize lines were more aligned towards the tropical than temperate inbred testers. This information would be useful for simplifying heterotic classification of the lines with profound implications for breeding progress. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Yields of maize ( Zea mays L.) are remarkably low in sub-Saharan Africa and yet farmers have limited access to improved varieties. The objective of this study was to determine combining ability and heterosis of 18 elite maize inbred lines in environments prone to northern corn leaf blight (NCLB) disease in the mid-altitude tropics. Nine elite inbred lines were crossed as females with nine male lines using the North Carolina Design II mating scheme and 81 hybrids were generated. The hybrids, parents and three standard check varieties were evaluated using an alpha lattice design with two replications across seven environments in the mid-altitude sub-humid agro-ecologies in Ethiopia. The new top ranking hybrids displayed up to 250 % high-parent heterosis and mid-parent heterosis for grain yield and up to −25 % high-parent mid-parent heterosis for NCLB reaction. The specific combining ability (SCA) by site interaction was not significant, suggesting that the top yielding hybrids were relatively stable across environments. Inbred lines such as CML 395, 30H83-7-1, ILO'OE-1-9, 124-b (113), CML202, CML312, and Gibe-1-91 resulted in significant SCA effects for grain yield were selected as promising parents. Lines CML395 and ILO'OE-1-9 had negative and significant general combining ability (GCA) effects for NCLB reaction, implying the resistance of the inbred lines for NCLB. The most performing experimental hybrids such as CML-312 × CML395, CML197 × CML395, CML443 × DE-78-Z-126-3 had high SCA effects and produced mean grain yields of >8 t ha. The new hybrids may be used directly for production or as testers in hybrid development with resistance to NCLB. [ABSTRACT FROM AUTHOR]

Bread wheat genotypes with slow rusting stem rust resistance were crossed in a half-diallel mating design to identify superior parents for stem rust resistance combined with high grain yield (GY) and related traits. Significant mid-parent heterosis for area under disease progress (AUDPC) was observed in crosses 7041-1 × Danda'a and Danda'a × Kubsa. H04-2 × Danda'a showed significant mid-parent heterosis for GY, thousand kernel weight (TKW), number of tillers per plant (TPP) and reduced plant height (PLH), and significant better-parent heterosis for GY. Significant general combining ability (GCA) effects for all characters and specific combining ability (SCA) effects for most of the traits indicated the contribution of additive and non-additive genes in the expression of these traits, respectively. GCA and SCA ratios ( $$\sigma_{\text{gca}}^{ 2} /\sigma_{\text{sca}}^{2}$$ ) were less than unity for GY, TKW and PLH, suggesting preponderance of non-additive gene action at F1 for these traits. Additive gene action was predominant in the inheritance of AUDPC, kernels per spike, TPP and days to maturity. H04-2, Digelu and Danda'a showed strong GCA effects for most of the characters investigated. Crosses 231545-1 × H04-2, 7041-1 × H04-2, Digelu × Kubsa and Danda'a × Kubsa were good combinations for AUDPC. H04-2 × Danda'a, Digelu × Kubsa and Danda'a × Kubsa were good combinations for GY and TKW. Overall, H04-2 and Danda'a were good general combiners, and crosses involved these lines performed well for most of the traits. Hence, these lines may be used in breeding programs to develop stem rust resistant and high yielding cultivars. [ABSTRACT FROM AUTHOR]

Like other small grain cereals, triticale (× Triticosecale Wittmack) is also affected by Fusarium head blight (FHB) which is a serious plant disease leading to yield losses and to a contamination of feed and food by harmful mycotoxins. Use of resistant varieties is the most effective way to manage FHB infections. More recently, commercial hybrid breeding in autogamous cereals has received increased interest. Therefore, we built a bridge between hybrid and resistance breeding and conducted a multi-environmental field trial using deliberate inoculation with Fusarium culmorum to: (i) evaluate different hybrid prediction approaches based on phenotypic and/or genomic data; (ii) compare the effect of cytoplasmic male sterility (CMS) inducing cytoplasm and normal (N) cytoplasm on FHB resistance. We evaluated 226 single cross hybrids, their paternal and maternal lines in both CMS- and N-cytoplasm. Our analysis revealed a large genetic variation for FHB resistance. Single cross hybrids tended to be more resistant than their parental lines. We observed a close association between N-lines and CMS-lines for FHB resistance. We found a predominance of σ over σ for FHB resistance. Correlation between the sum of general combining ability (GCA) effects and hybrid performance was high for FHB resistance. Mid-parent performance served as a moderate indicator for FHB resistance of single crosses. Best linear unbiased prediction of hybrid performance based on relatedness between tested and untested genotypes estimated by marker data showed great potential for hybrid prediction when no reliable per se information or GCA estimates are available. [ABSTRACT FROM AUTHOR]

Diallel crosses have been widely used for analysis of general combining ability (GCA), specific combining ability (SCA) and heterosis. In the present research, 12 lines were selected from 60 inbred rice bred by International Rice Research Institute with extremely-high or -low yielding records according to the previous three consecutive seasons of yield trial experiments, to construct a half diallel cross. The genetic distances (GDs) revealed by molecular markers for the 12 lines ranged from 0.2288 to 0.7169, averaging at 0.5882; clustering analysis showed the 12 lines were divided into four groups maintaining the original cluster structure of the 60 lines. The positive loci (PLs) including effective-increasing loci (ILs) and effective-decreasing loci (DLs) were screened. The results showed that hybrids derived from those parents with higher GCA effects had better performance for traits of yield and yield components. The SCA effects were strongly correlated to F performance as well as heterosis; the GDs based on ILs were significantly positive correlated to SCA effects and heterosis for yield and yield components while the GDs based on DLs showed the significant negative correlations. Based on this research, a new conception, i.e. general sum of combining ability (GSCA) was conceived, which is defined as the sum of GCAs for two parents of a hybrid. The GSCA and SCA showed similar correlations with traits of yield and yield components. The results illustrated that ILs could be used for further study on prediction of heterosis for traits of yield and yield components; and GSCA may be another considerable parameter combined with ILs for breeders in selecting elite hybrid. [ABSTRACT FROM AUTHOR]

Studies on tropical popcorn ( Zea mays L. ssp. mays) gene pools are still scarce. The objective of this study was to infer tropical popcorn gene pools by employing molecular and phenotypic information. Forty-eight inbred lines and 140 individuals belonging to the Viçosa and Beija-Flor popcorn populations were genotyped using 90 simple sequence repeat (SSR) and 93 single nucleotide polymorphism (SNP) markers, respectively. Grain yield and expansion volume were analyzed for the inbred lines and the hybrids obtained from intra- and interpopulation diallels. The cluster analysis based on SSR markers grouped 46 inbred lines into two groups according to their origin population. Principal coordinate and population structure analyses based on SSR and SNP markers confirmed the results from the clustering. For grain yield, midparent heterosis was greater in the interpopulation hybrids than in the intrapopulation hybrids. The genetic distance did not correlate with the specific combining ability effects and showed a week to intermediate correlation with hybrid performance and midparent heterosis. Based on the results from clustering, population structure, genetic diversity, heterosis and diallel analyses, Viçosa and Beija-Flor populations belong to distinct gene pools. Furthermore, inferring tropical popcorn gene pools might be more efficient if molecular marker and phenotypic data are combined. [ABSTRACT FROM AUTHOR]

Drought is the major abiotic stress limiting cocoa seedling survival during establishment. The level of genetic variation and relationship among traits related to drought tolerance were examined in a 6 × 6 incomplete diallel and 8 × 3 incomplete factorial mating designs for parents of diverse genetic groups. Thirty-eight families, 23 from the diallel and 15 from the factorial mating were evaluated in 2012/13 major dry season under shade and no-shade locations. Six-month old seedlings were planted in a randomized complete block design with two replications consisting of 24 plants per plot. Traits related to drought tolerance including stem growth, percentage survival, leaf chlorophyll content and plant vigour were monitored. Analysis of the 38 families showed highly significant ( P ≤ 0.01) variation for families, replications, locations and location × family interaction for most of the traits. Preponderance of additive effects was manifested in terms of significant GCA when genetic analysis of the diallel was performed. Heritability was moderate to high ( hb = 0.43-0.63) for broad sense and low to moderate ( hn = 0.25-0.57) for narrow sense. Clones PA 13 and AMAZ 15/15 had positive GCA effects, whereas PA 150 and T60/887 had negative GCA effects for most traits. The highest genotypic correlations were between survival and vigour. Results from the study indicate that there is considerable genetic variation for traits related to drought tolerance in the available germplasm, and the families of some specific clones are able to survive droughts under typical field conditions in Ghana. [ABSTRACT FROM AUTHOR]

U.S. maize germplasm has been considered as a new alternative source of favorable alleles to broaden the narrowing genetic base of temperate germplasm. However, direct utilization of diverse U.S. germplasm in target mega-environments could be hampered by limited adaptation-related information on parental performance or heterotic response in crosses with local germplasm. The objective of this study was to measure the performance of U.S. maize populations for broadening the Chinese germplasm base. Fifteen diverse U.S. populations were testcrossed to three local tester lines, representing Chinese heterotic groups A, B, and D, to evaluate parental adaptation and combining abilities for days to silking (DS), ear height (EH), and grain yield (GY) in target and intermediate mega-environments in northern China. There was genetic variability among U.S. maize populations for additive and non-additive effects for DS and GY, and predominant additive genetic effects for EH. All 15 U.S. populations, except for BS27 and BS31 due to slightly high EH, could be directly used in target mega-environments similar to the U.S. Corn Belt. U.S. populations BS11(HI)C7, BS13(S)C7, BS17(CB)C4, BS31, BSCB1(R)C12, and BSBB(SRCB)C4 had better effects for increasing GY. Favorable effects for DS were also observed in BS11(HI)C5 and BS31, for DS and EH in BS13(S)C7 and BSCB1(R)C12, and for EH in BSBB(SRCB)C4. The best strategies for utilizing these germplasms may be to introgress BS13(S)C7 and BS17(CB)C4 into group A, BS11(HI)C5 into group B, and BSCB1(R)C12 and BSBB(SRCB)C4 into group D to increase genetic variation within Chinese heterotic pools. [ABSTRACT FROM AUTHOR]

Predicting single-cross performance is of special interest in hybrid breeding of triticale. We used molecular and phenotypic data of factorial triticale crosses and compared several approaches to predict their single-cross performance. Twenty-three inbred lines and their 76 incomplete factorial crosses were field evaluated for grain yield, plant height, and heading time at five locations in Central Europe. In addition, the parental lines were genotyped with 52 SSR markers. Plant height and heading time were predicted with high accuracy based on mid-parent performance. In contrast, prediction of hybrid performance based on mid-parent value was not accurate for grain yield. Using general combining ability effects led to an enhanced prediction accuracy of hybrid grain yield performance. This accuracy could be slightly improved using best linear unbiased prediction approaches. The prediction accuracy was considerably high even if the number of tested hybrids was small. Consequently, best linear unbiased prediction of hybrid performance is a promising tool for hybrid triticale breeding programs. [ABSTRACT FROM AUTHOR]

Genetic distance analysis among quality protein maize (QPM) inbred lines and the correlation of genetic distance with heterosis would help to design breeding strategy and predict hybrid performance. This study was carried out to determine the amount of genetic diversity among QPM inbred lines using SSR markers and morphological distances; to classify the inbred lines according to their relationships; and to estimate the correlations of SSR markers and morphological distances with hybrid performance, heterosis and specific combining ability (SCA). One-hundred and five hybrids generated by diallel crossing of 15 QPM inbred lines were evaluated with the 15 parents for 17 morphological traits at Harare, Zimbabwe and Bako, Ethiopia and also examined for DNA polymorphism using 40 SSR markers. SSR markers and morphological methods of genetic distance estimates showed moderately high genetic distance among the inbred lines studied. Cluster analysis based on the two distance measures grouped the 15 parental lines differently. The SSR marker-based genetic distance was positively and highly significantly correlated with grain yield (r = 0.37), and negatively and highly significantly with days to anthesis (r = −0.40) and days to silking (r = −0.42). These relationships suggest that high grain yield and earliness of QPM hybrids can be predicted from SSR marker determined distances of the parents, although the correlation values were not very high. The correlations of SSR marker distance with heterosis were too low to be of predictive value except for the case of plant height. Morphological distances were of less importance in predicting hybrid performance and SCA effects of hybrids. [ABSTRACT FROM AUTHOR]

Cassava brown streak disease (CBSD) is an economically important virus disease causing significant losses to cassava root yield and quality in east, central and southern Africa. Breeding for resistance in cassava requires an understanding of the underlying genetic control of CBSD resistance. Sources of CBSD resistance are available but little is known on the value of those varieties as parents for CBSD resistance breeding. Two resistant and two susceptible varieties were crossed in a half diallel design and 35 F progeny from each of the six families, plus parents, were screened at two locations in a randomised complete block design with four replications in warm sub-humid environments of coastal Tanzania in 2008. Screening for CBSD field resistance was done using disease severity scoring on a scale of 1-5. Significant variations in disease severity were observed for crosses, general combining ability (GCA) and specific combining ability (SCA) at both locations. The CBSD shoot symptom severity scores ranged from 1 to 4.4 while root necrosis ranged from 1.3 to 4.5. The contribution of GCA to the total sum of squares of crosses for disease scores ranged from 86.9 to 95.2 % compared to SCA that ranged from 4.8 to 14.2 %. Additive gene effects were more important than non-additive effects indicating that CBSD resistance is genetically determined and that selection should be successful to improve resistance. Selection of parents with good GCA effects will be important for success in CBSD resistance breeding. [ABSTRACT FROM AUTHOR]

Maize ( Zea mays L.) is grown on 15 million ha in eastern and southern Africa. Several diseases are of common occurrence in the region and regularly result in significant yield losses. A collaborative regional disease nursery (REGNUR) project was initiated in 1998 to identify and increase access to disease resistant germplasm, generate and disseminate information on disease and insect resistance sources, and facilitate the development of resistant cultivars by project partners. A diallel among 12 elite inbred lines was formed with the specific objective of evaluating the combining ability of these inbred lines for grain yield and resistance to seven diseases. The trial was grown at six sites in 2001. Results showed that both general (GCA) and specific combining ability effects were significant for most diseases. On the average, GCA accounted for 69% of resistance to diseases and only 37% of variation for grain yield. Correlations between GCA effects for disease scores were generally non-significant, implying that it is possible to pyramid genes for disease resistance in inbred lines. This underscores the need for screening for resistance to prevailing diseases using artificial inoculation or reliable hot-spots. Based on GCA effects for grain yield and across diseases, P12 and P6 were the best inbred lines. The crosses P4 × P9 (6.7 t ha) and P4 × P12 (6.9 t ha) were the best hybrids in the earlier maturity group, while P3 × P9 (8.3 t ha) and P2 × P8 (7.4 t ha) were the best hybrids in the late maturity group. [ABSTRACT FROM AUTHOR]

A complete diallel cross study of six local populations of Iranian melon (Eyvanaki, Abasali, Tashkandi, Hose-sorkh, Mashhadi and Nahavand) and one foreign cultivar (Ananasi) was carried out. We investigated maturity, average weight per fruit, yield and acceptable yield in the pruning conditions over a period of two planting seasons. The analysis of variance for all of the characteristics indicated highly significant differences among genotypes. Additive gene effects were most important with respect to average weight per fruit and yield, while genetic dominance effects mainly controlled fruit maturity and acceptable yield. The reciprocal effects were significant for yield, acceptable yield and fruit maturity. Nahavand and Tashkandi had significant positive general combining ability effects for yield and acceptable yield. Favourable heterosis over the better parent was found for average weight per fruit, yield and acceptable yield. Thus, there is the potential to generate superior cultivars in segregant generation and hybrid production. [ABSTRACT FROM AUTHOR]

The aim of this work was to estimate the general and specific combining ability of peppers by measuring fruit quality and yield traits. This experiment was carried out on the garden field from Universidade Federal de Viçosa (UFV), Minas Gerais State—Brazil. Eight lines of Capsicum baccatum belonging to the UFV Horticultural Germplasm Bank were chosen based on their broad genetic and phenotypical background variation and then they were crossed in a complete diallel way. The F1 seeds of the 56 hybrids and eight parents were planted in the field in a randomized complete block design. The data were submitted to ANOVA and the means were grouped by Scott–Knott test ( P ≤ 0.01). Significant variation for fruit quality and yield components was observed among parents and F1 generation. Analysis of variance for the combining ability showed that GCA effects exhibited significant difference and SCA effects of the crosses were significant, except for the height of first bifurcation. For almost all characters both additive and non-additive effects influenced the performance of hybrids. [ABSTRACT FROM AUTHOR]

CIMMYT (International Maize and Wheat Research Institute) Zimbabwe’s early maturing maize program, which aims to supply seed to approximately 4 million hectares of maize area in eastern and southern Africa, lacks adequate information on heterotic relationships among early maturing germplasm and has no early maturing testers for hybrid development. Open-pollinated varieties (OPVs) and hybrids are the products targeted for this region. Among the hybrids, three-way and double-cross hybrids are desired. Thus the use of single crosses as testers would be an appropriate choice for such a breeding program as one could potentially identify three-way combinations during the early generation test. A twelve-parent diallel was formed and crosses evaluated to identify heterotic groups and single-cross testers. Crosses were evaluated under four different environments in Zimbabwe, two optimal, one low nitrogen stress and one drought stress. P5 (an early maturing line from heterotic group A) and CML 395 (a late maturing inbred line from heterotic group B) were used as reference parents to establish heterotic groupings of germplasm used in the diallel. The single cross (P7/P8) was identified as a potential group A tester because of: (a) co-classification of inbred lines into heterotic group A, (b) good yields-9.8 t/ha (optimal), 3.4 t/ha (low nitrogen) and 2.1 t/ha (drought); and (c) good GCA effects for grain yield (0.49 t/ha) of line P7 while line P8 contributed to reduced height and anthesis-silking interval. [ABSTRACT FROM AUTHOR]

Many common traits are believed to be a composite reflection of multiple genetic and environmental factors. Recent advances suggest that subtle variations in the regulation of gene expression may contribute to quantitative traits. The nature of sequence variation affecting the regulation of gene expression either in cis (that is, affecting the expression of only one of the two alleles in a heterozygous diploid) or in trans (that is, affecting the expression of both alleles in a heterozygous diploid) is a key and usually unknown feature for the breeders. If the change in expression acts entirely in cis, then the structural gene can be treated as a candidate gene and a potential target for marker-assisted selection. Therefore, gene surveys for cis-regulatory variation are a first step in identifying potential targets for marker-assisted breeding. Here, we discuss in detail the “genome-wide analysis of allele-specific expression differences” (GASED) approach. The GASED approach was developed to screen for cis-regulatory variation on a genome-wide scale. In GASED, mRNA abundance is treated as if it were a quantitative phenotypic response variable, whose genetic between-F1 hybrid variance is partitioned into additive and non-additive components. In plant breeding, this partitioning of the genetic variance is well known in the context of estimation of general and specific combining abilities for diallel crossing schemes. We demonstrate the GASED method using Arabidopsis thaliana data. The method can be used to screen for cis-regulatory variation in any crop species for which diallel crossing schemes are appropriate and genomic tools are available. [ABSTRACT FROM AUTHOR]

The objective of this study was to quantify the genetic variability and determine the inheritance of Al tolerance in lucerne (or alfalfa) using a 4-parent diallel mating design. Regrowth root length (RRL), along with root length (RL) and total root length (TRL), was measured to indicate relative Al stress response using a hydroponic system in a 3 μ M Al solution at pH 4.5. A diallel analysis indicated the significance of general combining ability ( gca) variance for RRL but not the specific combining ability ( sca) variance; the same result was obtained for TRL but not for RL. For both RRL and TRL, genetic variance appeared to be more important than the environmental variance. For RRL, a strong but non-significant correlation was indicated between parental performance and their gca effects; while mid-parent heterosis and/or over-dominance were detected, as associated with the expressed sca effects in several combinations. These results suggest the complex genetic nature and expression of Al tolerance in the 4-parent diallel crossing system tested. Al-tolerant parent, GAAT‘S’, was the most promising parent, conferring the highest gca effects for RRL as well as for other two characters. The existence of significant gca variance in RRL may also suggest the feasibility of improving Al tolerance through enhanced root regrowth using phenotypic recurrent mass selection to pyramid desirable Al-tolerant genes, focussing on parental lines and/or elite individual plants expressing long regrowth roots. [ABSTRACT FROM AUTHOR]

This research reports responses to selection and changes in general (GCA) and specific (SCA) combining abilities after three cycles of a modified reciprocal recurrent selection procedure (MRRS) in EPB-4 and EPB-5 maize populations. In the MRRS procedure a cycle can be completed in 1 or 2 years depending on the availability of winter breeding nurseries. The original and the three selection cycles of the two populations per se (eight entries) and the partial diallel developed from the crosses between them (16 entries) were evaluated in six environments. Realized response to selection on the population cross was 7.25% cycle−1 for grain yield, −13.63% cycle−1 for plant lodging, and 11.93% cyle−1 for prolificacy, whereas plant and ear heights remained unchanged. GCA estimates increased with selection cycles for both populations for grain yield and prolificacy, and decreased for plant lodging, indicating that the frequency of favorable alleles with additive effects for these traits increased with the MRRS cycles in both populations. SCA estimates increased for grain yield and prolificacy indicating that the frequency of favorable complementary alleles at loci with non-additive effects in the reciprocal populations increased with the MRRS cycles. For grain yield, SCA effects increased more than GCA effects with selection cycles, indicating that MRRS exploited more the non-additive effects than the additive effects for the improvement of this trait. The overall results showed that the MRRS procedure was highly effective in improving the population cross, exploiting both GCA and SCA effects. [ABSTRACT FROM AUTHOR]

The University of Minnesota Gaura breeding program is developing USDA Z3-4 winter-hardy genotypes via interspecific hybridization of G. lindheimeri (Z5-6) and G. coccinea (Z2-4). Prior to commencing interspecific hybridization, the reproductive barriers operating in both parental species need to be characterized. The objective of this research was to determine the type and stability of reproductive barriers operating in G. lindheimeri by statistical comparisons between pollen tube growth and seed set in a full-sib diallel. Slowed or aborted pollen tube growth in the style indicated the presence of a gametophytic self incompatibility (SI) system. A statistical method, female (FCC) and male (MCC) coefficients of crossability, was used to verify that a stable SI system was operating and that other reproductive barriers were present. Several genotypes also expressed stage-specific inbreeding depression and incongruity. The simple linear regression equation for FCC/MCC, using pollen tube growth, was Y = 0.0124 + 0.974X, which was much closer to the expected Y = 0.0 + 1.0X (indicating a stable SI system) than the equation for seed set, Y = 0.012 + 0.910X. Using pollen tube length, both general combining ability (GCA) and specific combining ability (SCA) values were highly significant for G. lindheimeri ( P ≤ 0.001). Histograms were used to delineate cut-offs to identify intra-incompatible/inter-compatible classes and S allele groups. Four possible classes were identified, but further research is needed to verify S allele genotypes. [ABSTRACT FROM AUTHOR]

The University of Minnesota Gaura breeding program is developing USDA Z3-4 winter-hardy genotypes via interspecific hybridization of G. lindheimeri (Z5-6) and G. coccinea (Z2-4). Prior to commencing interspecific hybridization, the reproductive barriers operating in both parental species need to be characterized. The objective of this research was to determine the type and stability of reproductive barriers operating in G. lindheimeri by statistical comparisons between pollen tube growth and seed set in a full-sib diallel. Slowed or aborted pollen tube growth in the style indicated the presence of a gametophytic self incompatibility (SI) system. A statistical method, female (FCC) and male (MCC) coefficients of crossability, was used to verify that a stable SI system was operating and that other reproductive barriers were present. Several genotypes also expressed stage-specific inbreeding depression and incongruity. The simple linear regression equation for FCC/MCC, using pollen tube growth, was Y = 0.0124 + 0.974X, which was much closer to the expected Y = 0.0 + 1.0X (indicating a stable SI system) than the equation for seed set, Y = 0.012 + 0.910X. Using pollen tube length, both general combining ability (GCA) and specific combining ability (SCA) values were highly significant for G. lindheimeri ( P ≤ 0.001). Histograms were used to delineate cut-offs to identify intra-incompatible/inter-compatible classes and S allele groups. Four possible classes were identified, but further research is needed to verify S allele genotypes. [ABSTRACT FROM AUTHOR]

The suitability of large-fruited apple cultivars as alternative donors of powdery mildew resistance to the crabapples carrying major gene resistances was assessed. Five accessions with varying levels of mildew resistance (‘Dülmener Rosen', ‘Liberty', ‘Sciros', ‘Prima' and ‘Red Delicious') and one susceptible cultivar (‘Cox's Orange Pippin') were mated in a partial diallel design, and sub-sets of each seedling family were evaluated for three years at three New Zealand sites (Havelock North, Riwaka and Clyde) with different climatic conditions. There was a high correlation among the powdery mildew susceptibility scores of the individual seedlings over the three years, but disease levels varied among sites, with those at Clyde being the highest. All accessions with some resistance were found to confer additive resistance to their progenies to varying degrees depending on the climatic conditions of the sites, but findings suggest that progeny selection at Clyde will be sufficient for breeding purposes. The performance of the cultivar itself was not necessarily a good predictor of the level of resistance conferred to its progenies. The mostly negative genetic correlations between powdery mildew scores and fruit quality attributes suggest that selecting for powdery mildew resistance and desirable fruit quality traits may not be difficult. However, a larger number of families may be needed for more precise estimates of the genetic correlations to strengthen confidence in this conclusion. [ABSTRACT FROM AUTHOR]

Little is known about the inheritance of agronomic traits in cassava, or on the relative importance of epistasis for most crops. A group of 10 clones, adapted to the acid-soils environment was used as parents in a diallel study. Thirty genotypes were obtained from each F1 cross and cloned. Each clone was represented by six plants, which were distributed in three replications at two contrasting locations. Genetic variability concentrated in the within-family component, which was statistically significant for all the variables analyzed (fresh root yield (FRY), fresh foliage yield (FFY), harvest index, root dry matter content, and plant type score (PTS)) except for the reaction to super elongation disease (SED). Estimates of dominance variance were considerably larger than those of additive variance for fresh root and foliage yields. The reverse was observed for harvest index, dry matter content, PTS and SED score. Epistasis played an important role only for fresh root and foliage productions. These results agree with those from similar studies targeting different environments. The common assumption of absence of significant epistatic effects frequent in many quantitative genetic designs is, therefore, challenged from the results for these two variables. Alternative breeding approaches are suggested according to the results obtained from this study. [ABSTRACT FROM AUTHOR]

Development of hybrids is considered to be a promising avenue to enhance the yield potential of crops. We investigated (i) the amount of heterosis observed in hybrid progeny, (ii) relative importance of general (GCA) versus specific (SCA) combining ability, and (iii) the relationship between heterosis and genetic distance measures in four agronomic traits of spring bread wheat. Eight male and 14 female lines, as well as 112 hybrids produced in a factorial design were grown in replicated trials at two environments in Mexico. Principal coordinate analysis based on Rogers' distance (RD) estimates calculated from 113 SSRs revealed three different groups of parents. Mid-parent heterosis (MPH) for grain yield averaged 0.02 t ha−1 (0.5%) and varied from −15.33% to 14.13%. MPH and hybrid performance (F1P) were higher for intra-group hybrids than for inter-group hybrids, with low values observed in inter-group crosses involving two non-adapted Chinese parents. Combined analyses of variance revealed significant differences among parents and among hybrids. Estimates of GCA variances were more important than SCA variances for all traits. Tight correlations of GCA with line per se performance, and mid-parent value with F1P were observed for all traits. In contrast, correlations of MPH with RD and coefficient of parentage were not significant. It was concluded that the level of heterosis in spring wheat was too low to warrant a commercial exploitation in hybrids. SSRs proved to be a powerful tool for the identification of divergent groups in advanced wheat breeding materials. [ABSTRACT FROM AUTHOR]

There is a limited knowledge on the inheritance of traits with agronomic relevance in cassava. A diallel study among 10 parental clones was conducted in the acid-soils environment in the eastern savannas of Colombia. Thirty clones were obtained for each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore, the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant effects for five of the six variables analyzed (harvest index, dry matter content, height of first branching, reaction to super elongation disease, and plant type scores). Fresh root yield showed strong genotype × environment interaction and differences between crosses reached statistical significance in only one of the two environments analyzed. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays an important role particularly in the cases of fresh root yield and harvest index. [ABSTRACT FROM AUTHOR]

Broccoli ( Brassica oleracea L., Italica Group) is a source of glucosinolates and their respective isothiocyanate metabolites that are believed to have chemoprotective properties in humans. Glucoraphanin (4-methylsulfinyl-butyl glucosinolate) is a predominant glucosinolate of broccoli. Its cognate isothiocyanate, sulforaphane, has proven a potent inducer of phase II detoxification enzymes that protect cells against carcinogens and toxic electrophiles. Little is known about the genetic combining ability for glucosinolate levels or the types of genetic variation (i.e., additive vs. dominance) that influence those levels in broccoli. In this study, a diallel mating design was employed in two field experiments to estimate combining abilities for glucoraphanin content. The diallel population was developed by crossing nine doubled-haploid (inbred) parents in all possible combinations (36), excluding the reciprocals. Horticultural traits of all entries were assessed on a plot basis. In fall 2001, glucoraphanin concentration of broccoli heads ranged from 0.83 to 6.00 μmol/gdw, and in spring 2002, ranged from 0.26 to 7.82 μmol/gdw. In both years, significant general combining ability was observed for glucoraphanin concentration and total head content, days from transplant to harvest, head weight, and stem diameter. Conversely, no significant specific combining ability was observed for any trait in either year. Results indicate that a given inbred will combine with others to make hybrids with relatively predictable levels of head glucoraphanin as well as, other important horticultural traits. This should allow identification of inbreds that typically contribute high glucoraphanin levels when hybridized with others. [ABSTRACT FROM AUTHOR]

Phenotypic variation and pattern of inheritance was investigated for plant and fruit traits in Japanese quince (Chaenomeles japonica, Maloideae). Japanese quince is a minor fruit crop in Latvia and Lithuania, and is presently being developed for production of juice, aroma and fruit fibre in Sweden and Finland. General and specific combining ability was estimated for five plant vegetative traits, eight fruit yield and morphology traits, and five fruit biochemistry traits in a study population consisting of 14 hybrid families. Thorniness seems to be controlled primarily by a single locus. All other traits studied appear to be governed primarily by additive genes, as judged from general combining ability estimates. Significant specific combining ability (SCA) was detected for yield, plant height and some fruit traits. However, the relative contribution of SCA to the overall genetic variance was in general low. An efficient breeding strategy for Japanese quince could therefore be based on recurrent selection. [ABSTRACT FROM AUTHOR]

A full diallel analysis is a tool for selection in plant breeding that has been subject to many discussions and controversies regarding its interpretation and merits. The analysis of well-defined transgenes by such an approach permits assessment of the value of diallel analyses. The performance of the Eberhart/Gardner diallel approach is analysed for the β-glucuronidase (GUS) activity of six well-defined, homozygous one-locus tobacco (Nicotiana tabacum L.) transgenic lines, each carrying differently located alleles of the GUS gene, and the nulliplex wild type. Tobacco is an inbreeding plant species, therefore all these lines are fully isogenic apart from the T-DNA insertion. The analysis shows that additivity of GUS gene activity as well as epistatic gene silencing translate well in the diallel parameters of general combining ability (GCA) and specific combining ability (SCA) or more detailed versions thereof, when compared to a parsimonious model based on the precise genetic constitution of the transgenic plants lines used as parents. The tobacco line with the highest GUS activity also has the highest GCA, demonstrating that an evaluation of parental phenotype would be sufficient for determining breeding potential. In case of the epistatic gene silencing, however, there is no positive correlation between GCA and parental performance, the reduction in GUS activity is more severe than is to be expected on the basis of parental performance. [ABSTRACT FROM AUTHOR]

A line × tester analysis was carried out in mulberry (Morus spp.) to determine the genetic interaction in the expression of various quantitative characters including leaf yield. Eight clonal varieties were selected, 3 of them were designated as lines (♀) viz. Berhampore-1, China white and MS-5 and 5 of them were called as testers (♂) viz. Mandalaya, Kosen, Assamjati, MS-1 and Kajli. Combining ability studies were conducted on these parents along with their F1 hybrids for the variables laminar index, growth rate, weight of 100 dry leaves, number of primary branches per plant, plant height, nodal distance, leaf-twig ratio, aerial biomass, moisture content, moisture retention capacity and leaf yield. Broad genetic variability was observed among the genotypes. The ratio of General Combining Ability (GCA) and Specific Combining Ability (SCA) indicated the predominance of non-additive genes in mulberry. While China white (female) and MS-1 (male) were the best general combiners among the parents, Berhampore-1 × Kajli was the best cross for leaf yield. Results suggest that selective crossing followed by proper screening may be the best approach for breeding of high yielding varieties in mulberry. [ABSTRACT FROM AUTHOR]

Genetic study in maize (Zea mays) germplasm development is an important step to understand the genetic variability and complementarity between heterotic groups, as well as additive and dominance genetic effects. Thus, diallel analyses have been widely adopted with the aim of identifying the best parental lines and the best crosses. In addition, different environmental conditions make genetic selection difficult. Thus, the objectives of this study were to compare individual and joint analyses of a diallel design through a mixed model methodology for maize breeding, and to evaluate and interpret the genetic effects and their interaction with the environmental effect. Thirteen F2 hybrids were crossed in an incomplete diallel scheme. Seventy-eight inter-population hybrids, and thirteen self-pollinated parents were evaluated. Eleven traits were evaluated, and emphasis was given to the Grain Yield (GY) trait. The significance of the GY trait, specifically, varied across environments. Joint analysis, in particular, presented significance for dominance and additive by environment interaction effects. Joint analysis had the highest selective accuracies for six traits. The correlation coefficients showed similar results, with values from 0.15 to 0.50 between pairs of environments. Gains with selection, considering each environment, ranged from 9.17 to 20.66%, when five hybrids were selected. When direct gains were compared with indirect gains, combined analysis confirmed the high efficiency of selection. For selection of parents, combined analysis achieves the same results as direct selection when two parents were selected. [ABSTRACT FROM AUTHOR]

In the past, extensive research has been conducted on breeding sweetpotato [Ipomoea batatas (L.) Lam] varieties with improved fresh root yields. However, little attention has been paid to breeding the crop for both improved storage root and vine yields for mixed crop-livestock farming systems. Consequently, the objective of this study was to determine gene action and heritability (H) of vine and root yield, and related yield components in sweetpotato. Eight parents selected for their contrasting attributes of root and vine production were hand-crossed in a half-diallel. Thirty-six generated families were evaluated at Rubona, Karama and Ngoma research stations of the Rwanda Agriculture Board. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant for fresh root yield (FRY), root dry matter content (RDMC), dry root yield (DRY), root-to-vine ratio, harvest index (HI) and vine dry matter content. GCA/SCA ratios were much greater than 0.5 for all the root parameters DRY, RDMC and FRY, with 0.75, 0.81 and 0.88, respectively, suggesting that additive gene action was more important than non-additive gene action. H estimates were above 0.5 for all tested parameters, with FRY, HI and RDMC having high estimates of 0.80, 0.81 and 0.92, in that order. Promising families were K5132/61 × Wagabolige, 2005-179 × RW11-1860, 4-160 × 2005-179, K5132/61 × RW11-1860, RW11-2910 × 2005-179, Ukerewe × SPK004 and Ukerewe × 4-160. Progenies derived from the selected families are recommended for further field testing in advanced selection stages at multiple sites for future release. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine general combining ability (GCA), specific combining ability (SCA), gene action and heritability of weevil (Cylass spp.) resistance, dry matter content (DMC), yield and yield-related components of newly developed sweetpotato clones. Six weevil resistant and six susceptible parents were crossed using a 6 × 6 factorial mating design. The resultant 36 families were evaluated at three locations using a 3 × 12 lattice design with two replications for weevil resistance and yield and related traits in western Tanzania. The GCA effect for females was significant except for percentage marketable root number (PMRN) and percentage marketable root yield (PMRY). Significant GCA effect of males were detected for all traits except PMRY. The SCA effect of families was significant for all traits. With a general predicted ratio (GPR) > 0.5, additive gene action controlled more the expression of total root number (TRN), root yield (RY), DMC, percentage infested root number (PIRN), percentage infested root yield and weevil damage score (WDS), whereas non-additive gene action controlled more the expression of PMRN and PMRY with a < 0.5 GPR. The narrow sense heritability for TRN, RY, DMC, PIRN and WDS were 0.24, 0.56, 0.84, 0.62 and 0.62, while the broad sense heritability for these traits were 0.58, 0.72, 0.93, 0.78 and 0.77, in that order. Four female parents and four male parents were identified as the best general combiners and 13 families recorded the best performance for the evaluated traits. The high heritability for most of the traits studded and presence of both additive and non-additive gene action for the traits suggests that genetic gain can be realized through hybridization and clonal selection in breeding programs. The selected parents and families are useful genetic resources for the development of sweetpotato genotypes resistant to weevils and enhanced root yield, yield components and DMC. [ABSTRACT FROM AUTHOR]