Mating Scheme Research Articles

Non-random mating and information theory

In this work, mate choice is modeled by means of the abstract concept of mutual mating propensity. This only assumes that different types of couples can have different mating success. The model is adequate for any population where mating occurs among distinct types. There is no extra assumption about particular mating scheme or preference model. The concept of mutual mating propensity permits to express the observed change in the mating phenotypes as the gain in information with respect to random mating. The obtained expression is a form of the Price equation in which the mapping between ancestral and descendant population is substituted by a mapping between random mating and non random mating population.At the same time, this framework provides the connection between mate choice and the exact mathematical partition of the choice effects, namely sexual isolation, sexual selection and a mixed effect. The sexual selection component is the sum of the intra-sexual male and female selection.The proposed framework helps to unveil previously hidden invariants. For example, if the mutual preference between partner types is multiplicative there is no sexual isolation (inter-sexual selection) effect on the frequencies, i.e. the only possible effect of mate choice is intra-sexual selection. On the contrary, whatever the contribution of each partner to the mutual preference, if it comes as a non-multiplicative factor, there is at least an inter-sexual selection detectable effect.This new view over the mate choice problem, permits to develop general mating propensity models and to make predictions of the mate choice effects that may emerge from such models. This possibility opens up the way for setting a general theory of model fitting and multimodel inference for mate choice.Thus, it is suggested that the proposed framework, by describing mate choice as the flow of information due to non-random mating, provides a new important setting for exploring different mating models and their consequences.

Recent advances for spermatogonial stem cell transplantation in livestock.

At the foundation of spermatogenesis are the actions of spermatogonial stem cells (SSCs), and a remarkable feature of these cells is the capacity to regenerate spermatogenesis following transplantation into testes of a recipient male that lacks endogenous germline. This ability could be exploited in livestock production as a breeding tool to enhance genetic gain. A key element to success is derivation of culture conditions that support proliferation of SSCs to provide sufficient numbers of cells for transfer into multiple recipient males. Using methodology devised for rodent cells as a foundation, advances in culturing cattle SSCs have occurred over the past few years and efforts are underway to extend this capability to pig cells. Another critical component to SSC transplantation is generation of males with germline ablation but intact somatic support cell function that can serve as surrogate sires for donor-derived spermatogenesis in a natural mating scheme. Recent advances in pigs using gene editing technologies have demonstrated that knockout of a key male germ cell-specific gene, namely NANOS2, leads to male-specific germline ablation but otherwise normal physiology, including intact seminiferous tubules. Together with recent advances in culturing spermatogonia of higher-order mammals, the now efficient means of producing germline-ablated recipient males have brought the application of SSC transplantation in livestock as a production tool closer to reality than ever before.

Genetic effect of Striga resistance in sorghum genotypes

Striga is an important parasitic weed causing substantial economic losses in cereal and legume crop production in sub-Saharan Africa. Integrated Striga management approaches such as a combined use of Striga resistant varieties and Fusarium oxysporum f.sp. strigae (FOS), a biocontrol agent of Striga, are an option to control the parasite and to boost sorghum productivity. Understanding host gene action influencing Striga resistance, with or without FOS treatment, is key to developing improved sorghum varieties with durable resistance and high yield. The objective of this study was to determine the gene action and inheritance of Striga resistance using genetically diverse populations of sorghum involving FOS treatment. Twelve sorghum parents selected for Striga resistance, FOS compatibility or superior agronomic performances were crossed using a bi-parental mating scheme. The selected male and female parents and their F1 progenies, backcross derivatives and the F2 segregants were field evaluated at three locations in Tanzania known for their severe Striga infestations using a lattice experimental design with two replications. The following data were collected and subjected to generation mean analysis (GMA): days-to-50% flowering (DFL), seed yield per plant (SYP) and number of Striga per plant (SN). GMA showed the preponderance of additive genetic action contributing to the total genetic variation in the evaluated sorghum populations. The additive genetic effect for DFL, SYP and SN, with and without FOS treatments, ranged from 72.02 to 86.65% and 41.49 to 95.44%, 75.62 to 91.42% and 71.83 to 91.89%, and 77.35 to 93.56% and 72.86 to 95.84%, in that order. The contribution of non-additive genetic effects was minimal and varied among generations. FOS application reduced DFL and SN and improved SYP in most of the tested sorghum populations. DFL of sorghum populations was reduced by a mean of 8 days under FOS treatment compared to the untreated control in families such as 675 × 654, AS435 × AS426 and 1563 × AS436. FOS treatment improved SYP with a mean of 6.44 g plant−1 in 3424 × 3993 and 3984 × 672. The numbers of Striga plants were reduced with a mean of 16 plants due to FOS treatment in the crosses of 675 × 654, 1563 × AS436, 4567 × AS424, and 3984 × 672. The study demonstrated that additive genes were predominantly responsible for the inheritance of Striga resistance in sorghum. Pure line cultivar development targeting reduced DFL, SN and high SYP in the selected populations may provide enhanced response to selection for integrated Striga management (ISM) programme.

Dynamic Gene-Resource Landscape Management of Norway Spruce: Combining Utilization and Conservation.

Traditional gene-resource management programs for forest trees are long-term endeavors requiring sustained organizational commitment covering extensive landscapes. While successful in maintaining adaptation, genetic diversity and capturing traditional growth attributes gains, these programs are dependent on rigid methods requiring elaborate mating schemes, thus making them slow in coping with climate change challenges. Here, we review the significance of Norway spruce in the boreal region and its current management practices. Next, we discuss opportunities offered by novel technologies and, with the use of computer simulations, we propose and evaluate a dynamic landscape gene-resource management in Norway. Our suggested long-term management approach capitalizes on: (1) existing afforestation activities, natural crosses, and DNA-based pedigree assembly to create structured pedigree for evaluation, thus traditional laborious control crosses are avoided and (2) landscape level genetic evaluation, rather than localized traditional progeny trials, allowing for screening of adapted individuals across multiple environmental gradients under changing climate. These advantages lead to greater genetic response to selection in adaptive traits without the traditional breeding and testing scheme, facilitating conservation of genetic resources within the breeding population of the most important forest tree species in Norway. The use of in situ selection from proven material exposed to realistic conditions over vast territories has not been conducted in forestry before. Our proposed approach is in contrast to worldwide current programs, where genetic evaluation is constrained by the range of environments where testing is conducted, which may be insufficient to capture the broad environmental variation necessary to tackle adaptation under changing climate.

Combining ability, heterosis, and genetic distance among nine elite American Pima cotton genotypes (Gossypium barbadense)

American Pima cotton (Gossypium barbadense L.) is grown in the southwest United States, and no Pima cotton hybrid is commercially grown. In this study, six commercial Pima cultivars (Pima S-7, Pima S-6, Phy 76, BR 007, DP 340, and DP 744) and three elite germplasm lines (SI 1331, 93252, and 8810) were crossed in a diallel mating scheme without reciprocals, and their 36 F2 and F3 progeny were planted in replicated tests at two locations (L) in 2004–2005. Yield and fiber traits were analyzed using Griffing’s Model 1, Method 2 diallel analysis. Genetic distance (GD) of parent lines was determined using 661 AFLP molecular markers. Across locations, significant genotype (G) and general combining ability (GCA) effects were detected for yield, boll size, lint percent, micronaire, 2.5% fiber length, fiber strength, and elongation. Significant specific combining ability (SCA) effects were detected for yield, micronaire, and strength. Lint yield and the yield components- boll size and lint percent exhibited significant G × L interactions. Significant GCA × L interactions occurred for yield and lint percent. Yield, boll size, and micronaire also had significant SCA × L interactions. No significant GCA or SCA by L interactions were detected for fiber length, strength, and elongation. The mean mid-parent heterosis (MPH) of the 36 hybrids in lint yield was low in F2, but non-existent in F3. Among the nine parents, Pima S-7 and DP 340 had the highest and significant positive GCA effects for lint yield, lint percent, and boll weight across tests. Only several F2 hybrids with Pima S-7 and DP 340 as one parent displayed some levels of useful heterosis in lint yield in the two locations, as compared to Pima S-7 as the check. MPH for other agronomic and fiber quality traits was low to non-existent in both generations. The average GD of the parents were not significantly correlated with their GCA effects, and GD between parents was also not correlated with SCA and MPH of their hybrids, with the exception of lint yield at the Las Cruces location where a significant negative correlation was obtained. However, GD of the parents was correlated with the performance of hybrids in lint yield, fiber length, fiber strength and elongation in one or two tests. This study represented one of the first studies to estimate heterosis, combining ability, and their relationship with genetic distance of parents in a representative subset of Pima cotton genotypes.

Gene Action Controlling Normalized Difference Vegetation Index in Crosses of Elite Maize (Zea mays L.) Inbred Lines

The quest for precise and rapid phenotyping of germplasm is increasing the interest of breeders and physiologists in the application of remote sensing techniques in maize breeding. Twenty-four drought-tolerant maize inbred lines were crossed using a modified North Carolina II mating scheme to generate 96 single-cross hybrids. The parents and the hybrids were evaluated under full irrigation and drought stress conditions in the dry seasons of 2010 and 2011 at Ikenne, southwest Nigeria. Normalized difference vegetation index (NDVI) was recorded at 3- and 8-leaf growth stages. Hybrids differed significantly for NDVI. Both general (GCA) and specific (SCA) combining ability effects were significant for NDVI measured at 8-leaf stage under both irrigation regimes, with GCA accounting for 53% of the total variation under full irrigation. Both additive and non-additive genetic effects played significant roles in the inheritance of NDVI. The females GCA effects for grain yield was positively correlated with females GCA effects for NDVI (r = 0.72, p < 0.0001) and the male GCA effects for grain yield was also correlated with males GCA effects for NDVI (r = 0.78, p < 0.0001) at 8-leaf stage under full irrigation. These results indicate that live green biomass accumulation in maize could be identified through early screening of a large number of genotypes using NDVI for developing productive hybrids.

Crossability Studies among Twenty Accessions of Roselle (Hibiscus sabdariffa L.)

Increasing exploitation of roselle (Hibiscus sabdariffa L.) and its products require that commercial varieties with superior attributes are developed to replace landrace varieties and to meet the growing demand for commercial-scale cultivation of the crop. In this study, twenty landrace varieties of roselle collected from three geographical regions of Ghana were artificially crossed in a pairwise mating scheme. The aim was to obtain relevant information pertaining to fertility status and extent of crossability among the accessions to facilitate breeding of improved varieties. Attempts at hybridisation were made both between and among 6 accessions of Hibiscus sabdariffa var Altissima and 14 accessions of Hibiscus sabdariffa var Sabdariffa. Crosses between accessions of Hibiscus sabdariffa var Altissima and Hibiscus sabdariffa var Sabdariffa yielded no hybrids, suggestive of a crossability barrier between the two mating groups. All intra-varietal crosses involving accessions of Hibiscus sabdariffa var Altissima were successful regardless of direction of cross while only few of the crosses among those of Hibiscus sabdariffa var Sabdariffa produced successful hybrids. Also fertility estimates of members of Hibiscus sabdariffa var Altissima were significantly higher (30.00%-80.00%) compared to those of var Sabdariffa (0.00%-43.00%). This implies that complete pairwise design could be used for intra-varietal crosses involving accessions of Hibiscus sabdariffa var Altissima, whereas only a partial pairwise design is feasible for members of Hibiscus sabdariffa var Sabdariffa.

Study of gene action for seed yield, oil and quality components in linseed (Linum usitatissimum L.)

An experiment was conducted to study the gene action of seed yield and quality components in linseed. The analysis of variance showed highly significant differences among the genotypes for all the quality traits. Graphical analysis exhibited non additive gene action playing major role for most of the attributes viz., seed yield per plant, harvest index, moisture content, oil content, protein content of seed, iodine value, palmitic acid, stearic acid and omega-3 content. Components of variance revealed the presence of additive components for oleic acid content and omega-6. Average degree of dominance ( 1/ )0.5 showed over dominance for all the traits except oleic acid contentand omega-6. The value of 2/4 1 indicated asymmetrical distribution of positive and negative genes showing dominance for all the characters. Utilization of biparental mating and recurrent selection schemes which has the virtue of effectively exploiting both additive and non-additive components was suggested for obtaining high yielding genotypes with better quality and high percentage of omega-3 fatty acid.

Heterosis and Combining Ability for Mineral Nutrients in Snowball Cauliflower (Brassica oleracea var. botrytis L.) Using Ogura Cytoplasmic Male Sterile Lines

Development of nutritionally rich hybrids is one of the main breeding objectives in vegetable crops to counter micronutrient malnutrition. The present study evaluates the combining ability and heterosis for different dietary minerals in snowball cauliflower. Five genetically diverse Ogura cytoplasmic male sterile (CMS) lines of cauliflower and seven male fertile testers were crossed in line × tester mating scheme to obtain 35 F1 hybrids. The assessment of the F1s along with their parental lines for 8 important macro- and microelements revealed a wide range of heterosis. The CMS line, Ogu 13-85 was identified as a good general combiner for sodium (Na), calcium (Ca), iron (Fe), zinc (Zn) and manganese (Mn) content, whereas Ogu 101 for Mn, Zn, sulphur (S) and magnesium (Mg) contents. The lines with better general combining ability (GCA) produced majority of the heterotic hybrids. However, GCA alone was not sufficient to determine and identify the potential parental lines. The hybrid, Ogu 101 × Lalchowk Maghi was found to be the best heterotic combination for potassium (K), S and Zn content. The cross Ogu 13-85 × Lalchowk Maghi was the best heterotic hybrid for Na and Ca content. The cross-combinations Ogu 13-85 × DB-187, Ogu 13-01 × DB-187 and Ogu 13-01 × Sel-26 showed high heterosis for accumulation of Mg, Fe and Mn, respectively. It was observed that both GCA and specific combining ability were important for heterosis of mineral content in snowball cauliflower.

GENOTYPE X ENVIRONMENT INTERACTION FOR GRAIN YIELD AND ITS COMPONENTS OF SOME YELLOW MAIZE CROSSES

Eight yellow maize (zea mays L.) inbred lines were crossed in half diallel mating scheme in 2013 season at Gemmeiza Agric. Res. Station giving a total of 28 crosses as hybrid seeds. In 2014 summer season, these 28 crosses were evaluated in a randomized complete blocks designs experiment with four replications at two locations and two densities i.e. 20 cm (D1) and 25cm (D2). Gemmeiza (L1) and Mallawy (L2). The whole study was designated as four different environmental conditions (L1D1, L1D2, L2D1 and L2D2) in each experiment. location mean squares had significant and high significant for days to 50% tasseling, plant height, ear height, ear length, number of rows / ear, number of kernels / row and grain yield (ard / fad. ) at D1 and D2. While, ear diamater and 100-kernel weight at D1 and days to 50% silking at D2 had significant location mean squares. Mean squares of densities exhibited significant and high significant for days to 50% tasseling and silking at L2 and ear diameter at L1. While, plant and ear heights, ear length, 100-kernel weight and grain yield / fad. had significant mean squares of densities, indicated that these traits changed their performance from location to another. Crosses mean squares were high significant for all traits under locations and densities meaning that, differences among the crosses under locations and densities were exited. Crosses x locations interaction mean squares had highly significant for days to 50% tassling, days to 50% silking and ear height at D1. Crosses x densities interactions mean squares had significant differences at four environments for most traits The interactions between crosses with the partitions; locations (L), densities (D) and (L x D) were significant for all traits, meaning that the crosses were affected by change of locations, densities and interaction of locations x densities.

Heritability, combining ability and inheritance of storage root dry matter in yam beans

Storage root dry matter content (RDM) is central to the improvement of consumer and industrial attributes of root crops. Yam bean ( Pachyrhizus species) is a legume root crop newly introduced in Uganda, but its adoption may be constrained by low RDM. The objective of this study was to investigate the magnitude of variance for general combining ability (GCA) and specific combining ability (SCA) effects, heritability estimates and inheritance of RDM in yam beans. Progenies of sixteen crosses, generated using the North Carolina (NCII) mating scheme, were evaluated in F 1 and F 2 field experiments, with three replications at the National Crops Resources Research Institute (NaCRRI), Namulonge in Central Uganda, during the first cropping seasons of April, 2013 and 2014, respectively. Significant (p<0.001) mean squares for general combining ability (GCA), and specific combining ability (SCA) were observed in F 1 and F 2 generations, demonstrating additive and non-additive genetic inheritance of RDM. High Baker’s ratio in F 1 (0.76) and F 2 (0.78), and large σ 2 GCA / σ 2 SCA (3.13) indicate predominance of additive gene effects. Narrow sense heritability was high in both F 1 (0.74) and F 2 (0.75), implying that RDM can be improved in yam beans through selection. The results provide a basis for selection of suitable parents for hybridisation and breeding programmes to develop high dry matter yam bean varieties in Uganda. Keywords: Baker’s ratio, gene action, Pachyrhizus species

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 R2 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, heterosis, genetic distance and their intercorrelations for waterlogging tolerance traits in chrysanthemum

Waterlogging tolerance (WT) is a major objective in chrysanthemum breeding programs, and although certain genotypes with different tolerance levels have been identified, their value as parents for WT breeding is unknown. Here, twelve F1 crosses derived from an incomplete diallel mating scheme were conducted to investigate combining ability and heterosis for WT and their relationships with parental genetic distance. The results showed that the membership function value of waterlogging (MFVW) was controlled by additive and non-additive gene effects, whereas other growth and biomass traits were mainly controlled by non-additive gene effects. The estimated broad and narrow sense heritabilities of the MFVW were 97.5 and 51.5%, respectively. Combining ability analyses indicated that ‘Nannong Xuefeng’ showing the largest general combining ability (GCA) effect for the MFVW was the best combiner, and identified several best cross combinations with high positive specific combining ability (SCA) effects for most WT-related traits. Mid- and high-parent heterosis occurred widely. The three distance measures, based on phenotypic traits (PD), molecular markers (GD) and markers linked with quantitative trait loci (QTL-GD), presented a non-significant correlation with combining ability except for the GD with GCA for the relative root fresh weight. The correlations between the QTL-GD and heterosis were significant for certain traits and generally higher than that of the PD or GD and heterosis. The SCA effects were positively correlated with heterosis for most of the WT traits (0.51 ≤ r ≤ 0.80). The findings benefit understanding the inheritance mode and then achieving desirable improvement for WT in chrysanthemum.

Diallel analysis and genetic diversity of some yellow maize inbred lines (Zea mays L.) using RAPD and SSR markers

Information about combining ability and genetic diversity among maize inbred lines is fundamental in designing breeding strategies for improving grain yield. Twenty one F1 hybrids were generated by crossing seven yellow maize inbred lines in a half diallel mating scheme in 2013 season. The 21 F1 hybrids plus the two check hybrids (SC166 and SC173) were evaluated in a randomized complete block design with three replications during 2014 season, to estimate combining ability effects and identify type of gene action governing the inheritance of grain yield and other important agronomic traits. Results showed that both general (GCA) and specific (SCA) combining ability mean squares were highly significant for all the studied characters. The GCA/SCA ratio was more than unity for all the studied traits, except days to 50% silking, plant height and grain yield, indicating the preponderance of the additive gene effects in the inheritance of these traits. The inbred line P1 appeared to be the best general combiner for earliness, grain yield and its components. The crosses P1×P2, P3×P7, P4×P7, and P5×P6 had the best SCA effects for grain yield and most of its component traits. The cross P1×P2 significantly out-yielded the two check hybrids (SC166 and SC173). The genetic diversity among the seven yellow parental inbred lines was assessed using two types of molecular markers; Random Amplified Polymorphic DNA (RAPD) and Simple Sequence Repeats (SSR). Seven random primers were used in the RAPD reactions, resulting in the amplification of 82 bands with 95.12% polymorphism. While, eight pairs of SSR primers were used and resulted in 49 fragments with 100% polymorphism. Genetic similarity among all possible pairs of inbred lines varied from 0.12 to 0.69, with an average of 0.34, for RAPD markers, and from 0.01 to 0.56, with an average of 0.24, for SSR markers. The similarity matrices for RAPD and SSR data were not significantly correlated (r=0.34, p >0.05). Genetic distances based on RAPD and SSR markers were insignificantly correlated with F1 hybrids grain yield, the correlation values being (r =0.02 and 0.429 P>0.05), respectively. Therefore, the parental genetic distance could not be used to predict the grain yield of the F1 hybrids in this study.

Genetic architecture of nonadditive inheritance in Arabidopsis thaliana hybrids

The ubiquity of nonparental hybrid phenotypes, such as hybrid vigor and hybrid inferiority, has interested biologists for over a century and is of considerable agricultural importance. Although examples of both phenomena have been subject to intense investigation, no general model for the molecular basis of nonadditive genetic variance has emerged, and prediction of hybrid phenotypes from parental information continues to be a challenge. Here we explore the genetics of hybrid phenotype in 435 Arabidopsis thaliana individuals derived from intercrosses of 30 parents in a half diallel mating scheme. We find that nonadditive genetic effects are a major component of genetic variation in this population and that the genetic basis of hybrid phenotype can be mapped using genome-wide association (GWA) techniques. Significant loci together can explain as much as 20% of phenotypic variation in the surveyed population and include examples that have both classical dominant and overdominant effects. One candidate region inherited dominantly in the half diallel contains the gene for the MADS-box transcription factor AGAMOUS-LIKE 50 (AGL50), which we show directly to alter flowering time in the predicted manner. Our study not only illustrates the promise of GWA approaches to dissect the genetic architecture underpinning hybrid performance but also demonstrates the contribution of classical dominance to genetic variance.

Resistance to Fusarium wilt in common bean

In breeding programs, understanding the potential of parents should be a way to spend significantly less time and costs to obtain new cultivars. For this, the objective of this study was to estimate the general and specific combining ability of parents aiming common bean breeding for resistance to Fusarium wilt (FW) based on disease severity and reduction in plant growth. Eight common bean genotypes were crossed in a 3 x 5 partial diallel mating scheme to obtain F1 hybrids. The parents and their 15 F1 hybrids were evaluated for severity of Fusarium wilt, area under the disease progress curve, percentage of plant height reduction and plant shoot fresh weight reduction and grain yield. The resistance of common bean to FW is controlled by a few dominant genes. The reduction in plant growth is controlled by a different set of genes that can increase the selection efficiency of parents for common bean breeding.

Genetic incompatibilities in sweetpotato and implications for breeding end-user preferred traits

Sweetpotatoes utilization is low in Ghana due to lack of farmer and consumer preferred cultivars. Poor flowering and incompatibilities among genotypes limit breeding progress in its improvement. The objective was to assess compatibilities among sweetpotato genotypes to select good parents for breeding end-user preferred varieties for increased utilization. Twenty-one genotypes selected from 115 accessions evaluated across three contrasting environments were crossed using full diallel mating scheme. In all, 6388 crosses were carried out and 3214 seeds produced. This study sought to understand the genetic incompatibilities based on the number of seeds set per capsule after self- or cross-fertilization. Lack of flowering or poor flowering, and self- and cross-incompatibilities were major constraints to sweetpotato improvement found. Four genotypes (Histarch, Apomuden, Beauregard, and Ogyefo) were the best parents based on cross compatibilities and they can be used to determine the genetic control of beta-carotene, dry matter and sugar contents in sweetpotato. Histarch and Ogyefo are recommended as parents for the development of non-sweet, high dry matter sweetpotato varieties that are the preferred cultivars in Ghana because of their low sugar content. Use of many genotypes in hybridization and establishment of crossing blocks Hybridization in the minor cropping season is highly recommended.

Preliminary investigation of the crossing of bambara nut (&lt;i&gt;Vigna subterranea&lt;/i&gt; [L.] Verdc.)

Effective crosses among selected parents are crucial for genetic analyses and for the breeding of crop plants. Bambara nut is an indigenous African legume with considerable genetic diversity useful for genetic enhancement of yield and quality traits through breeding. However, the crop has previously received limited research attention. This may be attributed to its extremely small flower size, its flower orientation, the delicate nature of the flower and it’s mating system. The aim of this study was to establish a preliminary crossing protocol for Bambara nut for breeding and genetic studies. Controlled emasculation and pollination were performed using eight selected parents, using a diallel mating scheme under glasshouse conditions. Some successful crosses were achieved and F1 seeds were recovered from the crosses of 211-40-1 x N211-2, N212-8 x 211-40-1 and M09-3 x 211-82-1. Keywords : Bambara nut, emasculation, crossing, pollination, F 1 hybrids Ahmadu Bello University Zaria, Nigeria

Effect of assortative mating on genetic gain and inbreeding in aquaculture selective breeding programs

In this simulation study, the effect of the mating scheme on genetic gain and inbreeding has been explored for aquaculture selection programs where tank effects and large family sizes are common. Different selection methods were investigated (individual, family, sib, combined and within-family selection). Our results suggest that under family and sib selection, genetic gain was increased with assortative mating in comparison to random mating. The advantage of assortative mating increased when common environmental effects were present. Contrarily, a decrease in genetic gain was observed with disassortative mating, except for the case of within-family selection. The advantage of assortative mating over random mating was due to the increase in the between-family component of the additive genetic variance that was exacerbated with the presence of common environmental effects. Under family and sib selection, the join effect of assortative mating and common environmental effects produced an increase in genetic gain of around 80 and 40% at early generations, and around 10 and 60% at later generations, respectively. Inbreeding was low under family selection for all mating schemes but much higher under sib selection when assortative mating was performed. In fact, the inbreeding coefficient after 10 generations of selection was 300% higher when assortative matings were performed under sib selection, compared to random matings. This was due to the fact that under sib selection, matings were based on family means, leading to an increased frequency of within-family matings. To our knowledge, this is the first study that investigates the effect of the mating scheme on genetic gain and inbreeding in an aquaculture context where family sizes are large and tank effects are present, and shows that assortative mating can substantially enhance the response to selection, particularly when family selection methods are applied. Statement of relevanceOur article complies with the Policy Statement for submission of manuscripts to the Genetics Section, as it provides insight into the issue of breeding programs. Here, we have connected previous work in the field to address new questions, focusing on how the mating scheme may affect both genetic gain and inbreeding in aquaculture selection programs, where family sizes are typically large and tank effects are usually present.In fish species, it is possible to consider different mating schemes because fecundity is high and because in vitro fertilization is often possible. A particular problem in aquaculture breeding programs is the impossibility of tagging physically newborn individuals. Given this, a common practice in aquaculture is to rear families in separate tanks until the fish are large enough to be individually tagged. This introduces an environmental effect common to the members of the same family (tank effect) which can lead to a reduction of the response to selection that needs to be considered.We studied here the efficiency of different selection methods in terms of genetic gain and inbreeding and investigated the effect of the mating scheme to optimize breeding programs in aquaculture when tank effects are present. We have shown that assortative mating can substantially enhance the response to selection, particularly when family selection methods are applied and tank effects are present. To our knowledge, the effect of the mating scheme in an aquaculture context has never been addressed before. Our results suggest that assortative mating in the presence of common environmental variance may be considered in selection programs in aquaculture. Our conclusions will help breeders make optimal mating choices.

Genetic analysis of resistance to Alternaria leaf petiole and stem blight of sweetpotato in Uganda

Alternaria blight (Alternaria spp.) is an important sweetpotato disease in Uganda causing yield losses of over 50 % in susceptible genotypes. In Uganda, Alternaria bataticola and Alternaria alternata are the major species with A. bataticola the more aggressive of the two. The most effective control measure for this disease is the use of resistant genotypes. This study was conducted to determine the inheritance of resistance to Alternaria blight and the general and specific combining abilities of the available germplasm. Sixteen parental clones varying in reaction to Alternaria blight were crossed using the North Carolina II mating scheme. Due to incompatibility of some parents, two sets of compatible parents were formed. Differences among the families for Alternaria blight severity were significant while general combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant (P < 0.001) for the disease with GCA sum of squares (SS) being more predominant at 67.4 % of the treatment SS for Set 1 and the SCA SS predominant at 54.0 % of the treatment SS for Set 2. This indicated that both additive and non-additive effects are important in controlling this trait. Some parents with high, negative GCA effects produced families with undesirable SCA effects and the reverse was also true. This implies that the best parents should not be chosen on GCA alone but also on SCA of their best crosses. The wide range in the area under disease progress curve for the families indicated that it was possible to select for highly resistant genotypes.