HETEROSIS IN CHICKPEA FOR GRAIN PRODUCTIVITY IN EMBU COUNTY, KENYA

Chickpea is a major source of proteins especially in arid and semi-arid areas of Kenya. However, its average yield per hectare is low when compared to neighbouring countries. This research was carried out to determine the levels of hybrid vigour on yield in the F1 generation. To obtain the F1s, reciprocal crossing between Mwanza 2 and Chaina I was carried out with controls being the parental lines. The experimental layout was a randomized block design replicated thrice for three seasons. A spacing of 50x20cm was used in plants, while all other agronomic practices were maintained constant. Data on grain yield and biomass per plant was obtained by measuring the weight, then subjecting it to a one-way ANOVA in SAS 9.4 software. Mwanza 2 expressed the highest biomass (2.56g), while both parents attained a maximum grain yield of 1.69g per plant. Chaina I x Mwanza 2 hybrid expressed maximum means of F1s for biomass (2.31g) and grain yield (1.4g) per plant. Chaina I x Mwanza 2 hybrid recorded the highest biomass and grain yield in better parent heterosis with 14.36% and 330% respectively. Mid-parent heterosis means were also highest at 24.53% and 405.88% for biomass and grain yield respectively. Further, the heritability was maximum for biomass under Mwanza 2 x Chaina I, varying from 93.1% to 100%, while Chaina I x Mwanza 2, expressed maximum grain yield and harvest index. Better parent heterosis and mid-parent heterosis was highest in Chaina I x Mwanza 2 than its reciprocal, Mwanza 2 x Chaina I.

Mutant alleles differentially shape fitness and other complex traits in cattle

Mutant alleles (MAs) that have been classically recognised have large effects on phenotype and tend to be deleterious to traits and fitness. Is this the case for mutations with small effects? We infer MAs for 8 million sequence variants in 113k cattle and quantify the effects of MA on 37 complex traits. Heterozygosity for variants at genomic sites conserved across 100 vertebrate species increase fertility, stature, and milk production, positively associating these traits with fitness. MAs decrease stature and fat and protein concentration in milk, but increase gestation length and somatic cell count in milk (the latter indicative of mastitis). However, the frequency of MAs decreasing stature and fat and protein concentration, increasing gestation length and somatic cell count were lower than the frequency of MAs with the opposite effect. These results suggest bias in the mutations direction of effect (e.g. towards reduced protein in milk), but selection operating to reduce the frequency of these MAs. Taken together, our results imply two classes of genomic sites subject to long-term selection: sites conserved across vertebrates show hybrid vigour while sites subject to less long-term selection show a bias in mutation towards undesirable alleles.

Little heterosis found in Diploid Hybrid Potato

Hybrid potato breeding has become a novel alternative to conventional potato breeding allowing breeders to overcome intractable barriers (e.g. tetrasomic inheritance, masked deleterious alleles, obligate clonal propagation) with the benefit of seed-based propagule, flexible population design, and the potential of hybrid vigour. Until now, however, no formal inquiry has adequately examined the relevant genetic components for complex traits in hybrid potato populations. In this present study, we use a two-step modelling approach to estimate the relevant variance components to assess the magnitude of the general and specific combining abilities (GCA and SCA, respectively) in diploid hybrid potato (DHP). SCA effects were identified for all yield components studied here warranting evidence of non-additive genetic effects in hybrid potato yield. However, the estimated GCA effects were on average two times larger than their respective SCA quantile across all yield phenotypes. Tuber number GCAs and SCAs were found to be highly correlated with total yield's genetic components. Tuber volume appearing under-selected in this population. The prominence of additive effects found for all traits presents evidence that breeders can perform hybrid potato evaluation using the mid-parent value alone. Heterotic vigour stands be useful in bolstering simpler traits but this will be very dependent on the target market of a population. This study represents the first diallel analysis of its kind in diploid potato using material derived from a commercial hybrid breeding programme.

Fitness consequences of targeted gene flow to counter impacts of drying climates on terrestrial-breeding frogs

Targeted gene flow (TGF) could bolster the adaptive potential of isolated populations threatened by climate change, but could also lead to outbreeding depression. Here, we explore these possibilities by creating mixed- and within-population crosses in a terrestrial-breeding frog species threatened by a drying climate. We reared embryos of the crawling frog (Pseudophryne guentheri) on wet and dry soils and quantified fitness-related traits upon hatching. TGF produced mixed outcomes in hybrids, which depended on crossing direction (origin of gametes from each sex). North-south crosses led to low embryonic survival if eggs were of a southern origin, and high malformation rates when eggs were from a northern population. Conversely, east-west crosses led to one instance of hybrid vigour, evident by increased fitness and desiccation tolerance of hybrid offspring relative to offspring produced from within-population crosses. These contrasting results highlight the need to experimentally evaluate the outcomes of TGF for focal species across generations prior to implementing management actions.

First successful hybridization experiment between native European weatherfish (Misgurnus fossilis) and non-native Oriental weatherfish (M. anguillicaudatus) reveals no evidence for postzygotic barriers

The European weatherfish Misgurnus fossilis (Linnaeus, 1758) is a threatened freshwater species in large parts of Europe and might come under pressure from currently establishing exotic weatherfish species. Additional threats might arise if those species hybridize which has been questioned in previous research. Regarding the hybridization of M. fossilis × M. anguillicaudatus (Cantor, 1842), we demonstrate that despite the considerable genetic distance between parental species, the estimated long divergence time and different ploidy levels do not represent a postzygotic barrier for hybridization of the European and Oriental weatherfish. The paternal species can be easily differentiated based on external pigment patterns with hybrids showing intermediate patterns. No difference in standard metabolic rate, indicating a lack of hybrid vigour, renders predictions of potential threats to the European weatherfish from hybridization with the Oriental weatherfish difficult. Therefore, the genetic and physiological basis of invasiveness via hybridization remains elusive in Misgurnus species and requires further research. The existence of prezygotic reproductive isolation mechanisms and the fertility of F1 hybrids remains to be tested to predict the potential threats of globally invasive Oriental weatherfish species.

Eragrostis curvula, a Model Species for Diplosporous Apomixis

Eragrostis curvula (Schrad.) Ness is a grass with a particular apomictic embryo sac development called Eragrostis type. Apomixis is a type of asexual reproduction that produces seeds without fertilization in which the resulting progeny is genetically identical to the mother plant and with the potential to fix the hybrid vigour from more than one generation, among other advantages. The absence of meiosis and the occurrence of only two rounds of mitosis instead of three during embryo sac development make this model unique and suitable to be transferred to economically important crops. Throughout this review, we highlight the advances in the knowledge of apomixis in E. curvula using different techniques such as cytoembryology, DNA methylation analyses, small-RNA-seq, RNA-seq, genome assembly, and genotyping by sequencing. The main bulk of evidence points out that apomixis is inherited as a single Mendelian factor, and it is regulated by genetic and epigenetic mechanisms controlled by a complex network. With all this information, we propose a model of the mechanisms involved in diplosporous apomixis in this grass. All the genetic and epigenetic resources generated in E. curvula to study the reproductive mode changed its status from an orphan to a well-characterised species.

Compensation of Wild Plants Weakens the Effects of Crop-Wild Gene Flow on Wild Rice Populations

Crop-wild gene flow may alter the fitness of the recipient i.e., crop-wild hybrids, then potentially impact wild populations, especially for the gene flow carrying selective advantageous crop alleles, such as transgenes conferring insect resistance. Given the continuous crop-wild gene flow since crop domestication and the occasionally stressful environments, the extant wild populations of most crops are still “wild.” One interpretation for this phenomenon is that wild populations have the mechanism buffered for the effects of crop alleles. However, solid evidence for this has been scarce. We used wild rice (Oryza rufipogon) and transgenic (Bt/CpTI) rice (O. sativa) as a crop-wild gene flow model and established cultivated, wild, and F7 hybrid rice populations under four levels of insect (Chilo suppressalis) pressure. Then, we measured the trait performance of the plants and estimated fitness to test the compensatory response of relatively high fitness compared to the level of insect damage. The performance of all plants varied with the insect pressure level; wild plants had higher insect-tolerance that was expressed as over- or equal-compensatory responses to insect damage, whereas crop and hybrids exhibited under-compensatory responses. The higher compensation resulted in a better performance of wild rice under insect pressure where transgenes conferring insect resistance had a somewhat beneficial effect. Remarkable hybrid vigour and the benefit effect of transgenes increased the fitness of hybrids together, but this joint effect was weakened by the compensation of wild plants. These results suggest that compensation to environmental stress may reduce the potential impacts of crop alleles on wild plants, thereby it is a mechanism maintaining the “wild” characteristics of wild populations under the scenario of continuous crop-wild gene flow.

Hybrid Vigour Study of Yield and Yield Related Characters on Limmu Coffee (Coffea arabica L.) Genotypes at South-Western Ethiopia

Coffee (Coffea arabica L.) is one of the most important crops cultivated worldwide and has a great economic impact in many countries including Ethiopia. Hybrid vigor (heterosis) breeding can enhance productivity of coffee. Hybrid vigor study was conducted on 5 x 5 half-diallel mating involving 17coffee genotypes (5 parents, 10 F1 hybrids and two checks) for yield and its related traits in 2018. The study locations include Jimma, Agaro and Gera research centers of south-western Ethiopia using randomized completely block design with three replications. There are significant differences among 17 genotypes and 15 diallel genotypes (checks excluded) for all traits; the crosses showed significant and positive average heterosis (mid parent) and heterobeltiosis (better parent) for all traits. Crosses showed significant variation in the expression of standard heterosis (SH) and useful heterosis (UH) for fruit length (FL), fruit width (FW), bean length (BL), bean width (BW), bean thickness(BT), and hundred bean weight (HBW) across locations. Heterobeltiosis ranged from -9.06 to 88.79% and -17.81 to 67.98% for yield at Jimma and Gera, respectively. Mean SH and UH was positive and between 5 and 10% for BL and BT and <5% for all fruit characters and BT across locations. Mean of SH and UH was 14.62% and 11.82%, respectively for HBW. Crosses P4 x P5, P1 x P5 and P2 x P5 increased yield by 25.13% (637.75 kg), 14.05% (356.64 kg) and 5.78% (146.59 kg) over commercial pure line variety across three locations, respectively. Based on heterosis and mean performance hybrids P4 x P5, P1 x P5, P3 x P5, and P1 x P2 found as promising hybrids for yield and bean characters. Thus, these hybrids should be advanced in the next breeding program and tested through incorporating other traits.