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Developmental evolution and diversification of morphology can arise through changes in the regulation of gene expression or protein-coding sequence. To unravel mechanisms underlying early developmental evolution in cavefish of the species Astyanax mexicanus, we compared transcriptomes of surface-dwelling and blind cave-adapted morphs at the end of gastrulation. Twenty percent of the transcriptome was differentially expressed. Allelic expression ratios in cave X surface hybrids showed that cis-regulatory changes are the quasi-exclusive contributors to inter-morph variations in gene expression. Among a list of 108 genes with change at the cis-regulatory level, we explored the control of expression of rx3, which is a master eye gene. We discovered that cellular rx3 levels are cis-regulated in a cell-autonomous manner, whereas rx3 domain size depends on non-autonomous Wnt and Bmp signalling. These results highlight how uncoupled mechanisms and regulatory modules control developmental gene expression and shape morphological changes. Finally, a transcriptome-wide search for fixed coding mutations and differential exon use suggested that variations in coding sequence have a minor contribution. Thus, during early embryogenesis, changes in gene expression regulation are the main drivers of cavefish developmental evolution.

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Transferring an asexual mode of reproduction by seeds (apomixis) to cultivated plants would enable clonal reproduction of heterozygous genotypes such as F1 hybrids with hybrid vigor (heterosis), facilitating their access and multiplication by small-scale growers. Although sources of apomixis and the genetic loci controlling its constituent elements have been identified in wild species, their transfer by crossing to cultivated species has so far been unsuccessful. Here, we have introduced synthetic apomixis in hybrid rice to produce a high (95-100%) frequency of clonal seeds, via the inactivation of three meiotic genes-resulting in unreduced, non-recombined gametes-and the addition of an egg cell parthenogenesis trigger. The genotype and phenotype, including grain quality, of the F1 hybrid are reproduced identically in the clonal apomictic progenies. These results make synthetic apomixis compatible with future use in agriculture.

Le transfert d'un mode de reproduction clonale asexuée par grain (apomixie) aux plantes cultivées permettrait de reproduire de façon génétiquement identique des génotypes hétérozygotes comme ceux des hybrides F1 dotés d'une vigueur hybride (heterosis), facilitant ainsi leur accès et leur multiplication par les petits cultivateurs. Bien que des sources d'apomixie et les loci génétiques contrôlant ses éléments constitutifs aient été identifiés chez les espèces sauvages, leur transfert par croisement aux espèces cultivées a jusqu'à présent été infructueux. Ici, nous avons introduit chez un riz hybride une apomixie synthétique produisant une haute fréquence de grains clonaux (95­100%), via l'inactivation de trois gènes méiotiques ­ permettant d'obtenir des gamètes non réduits et non recombinés ­ et l'apport d'un déclencheur de la parthénogenèse. Le génotype et le phénotype, incluant la qualité de grain, de l'hybride F1 sont reproduits à l'identique dans les descendances apomictiques clonales. Ces résultats rendent compatible l'apomixie synthétique avec une future utilisation en agriculture.

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Pigeons and doves (family Columbidae) are one of the most diverse extant avian lineages, and many species have served as key models for evolutionary genomics, developmental biology, physiology, and behavioral studies. Building genomic resources for columbids is essential to further many of these studies. Here, we present high-quality genome assemblies and annotations for 2 columbid species, Columba livia and Columba guinea. We simultaneously assembled C. livia and C. guinea genomes from long-read sequencing of a single F1 hybrid individual. The new C. livia genome assembly (Cliv_3) shows improved completeness and contiguity relative to Cliv_2.1, with an annotation incorporating long-read IsoSeq data for more accurate gene models. Intensive selective breeding of C. livia has given rise to hundreds of breeds with diverse morphological and behavioral characteristics, and Cliv_3 offers improved tools for mapping the genomic architecture of interesting traits. The C. guinea genome assembly is the first for this species and is a new resource for avian comparative genomics. Together, these assemblies and annotations provide improved resources for functional studies of columbids and avian comparative genomics in general.

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With recent evidence of hybridization events in the field, the phenotypic traits of F1 hybrid colonies of 2 destructive subterranean termite species, Coptotermes formosanus Shiraki and Coptotermes gestroi (Wasmann) remain to be investigated. In this study, laboratory colonies of 2 conspecific pairings and 2 heterospecific pairings (hybrid F = ♀C. formosanus × ♂C. gestroi, hybrid G = ♀C. gestroi × ♂C. formosanus) were examined in Florida, USA, and in Taiwan. Colony nest architecture for both hybrids displayed disorganized carton materials compared to the defined trabecular carton of both parental species. Soldier head measurements were not a reliable approach for diagnostic purposes, as soldier morphometric traits widely overlapped across all mating combinations, except for hybrid F soldiers displaying abnormally long mandibles. Hybrid F soldiers' mandibles also remained parallel when at rest. However, 4 qualitative morphological differences in soldiers were determined for diagnostic purposes. First, the fontanelle in both hybrids is horizontally ellipsoid whereas subcircular in C. gestroi and trianguliform in C. formosanus. Second, sclerotized striations along the postmental sulcus are present in C. gestroi, absent in C. formosanus, and intermediate in both hybrid soldier types. Third, each lateral margin of the fontanelle is flanked by 2 setae in C. formosanus and both hybrids, while a single seta resides on each side of the fontanelle in C. gestroi. Finally, C. gestroi and hybrid soldiers' heads are characterized by a bulging vertex that is lacking in C. formosanus. Therefore, a combination of these 4 characteristics now allows for soldier identification of hybrid Coptotermes.

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BACKGROUND: Genomic imprinting affects gene expression in a parent-of-origin manner and has a profound impact on complex traits including growth and behavior. While the rat is widely used to model human pathophysiology, few imprinted genes have been identified in this murid. To systematically identify imprinted genes and genomic imprints in the rat, we use low input methods for genome-wide analyses of gene expression and DNA methylation to profile embryonic and extraembryonic tissues at allele-specific resolution. RESULTS: We identify 14 and 26 imprinted genes in these tissues, respectively, with 10 of these genes imprinted in both tissues. Comparative analyses with mouse reveal that orthologous imprinted gene expression and associated canonical DNA methylation imprints are conserved in the embryo proper of the Muridae family. However, only 3 paternally expressed imprinted genes are conserved in the extraembryonic tissue of murids, all of which are associated with non-canonical H3K27me3 imprints. The discovery of 8 novel non-canonical imprinted genes unique to the rat is consistent with more rapid evolution of extraembryonic imprinting. Meta-analysis of novel imprinted genes reveals multiple mechanisms by which species-specific imprinted expression may be established, including H3K27me3 deposition in the oocyte, the appearance of ZFP57 binding motifs, and the insertion of endogenous retroviral promoters. CONCLUSIONS: In summary, we provide an expanded list of imprinted loci in the rat, reveal the extent of conservation of imprinted gene expression, and identify potential mechanisms responsible for the evolution of species-specific imprinting.

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A large portion of basic biomedical research studies are conducted using genetically defined, inbred mouse strains. The C57BL/6 mouse strain is the most widely used genetic background in current rodent research. The rationale for using inbred strains is that all individuals are genetically identical with minimal phenotypic variation, allowing for more statistically powerful analyses. F1 hybrids between two inbred strains are also genetically identical to one another but are heterozygous at every locus at which the parental strains differ rather than homozygous. Both theoretical and empirical evidence suggests that this heterozygosity in F1 hybrids allow for potentially greater resilience in response to the inevitable stresses of laboratory environments. The purpose of this study was to characterize the differences in commonly used tests of physical performance (forelimb grip strength and rotarod) and anxiety-like behavior between the F1 hybrids created from BALB/c females mated to C57BL/6 males (called CB6F1 mice) and one of its parental strains, C57BL/6. We used a natural cross-fostering breeding scheme to minimize maternal care effects and emphasize the effects of genetic differences. We found significant correlations between anxiety-like behavioral measures and physical performance measures which are not traditionally associated with anxiety-like behavior, and which differ between strains. Findings from this study should be taken into consideration when designing behavioral studies and choosing model organisms.

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Research on diploid hybrid potato has made fast advances in recent years. In this review we give an overview of the most recent and relevant research outcomes. We define different components needed for a complete hybrid program: inbred line development, hybrid evaluation, cropping systems and variety registration. For each of these components the important research results are discussed and the outcomes and issues that merit further study are identified. We connect fundamental and applied research to application in a breeding program, based on the experiences at the breeding company Solynta. In the concluding remarks, we set hybrid breeding in a societal perspective, and we identify bottlenecks that need to be overcome to allow successful adoption of hybrid potato.

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The genetic linkage maps of the traditional F2 population in inbred lines were estimated from the frequency of recombination events in both parents, providing full genetic information for genetic and genomic studies. However, in outbred forest trees, it is almost impossible to generate the F2 population because of their high heterozygosity and long generation times. We proposed a novel strategy to construct an integrated genetic linkage map that contained both parental recombination information, with restriction-site-associated DNA sequencing (RADSeq) data in an F1 hybrid population of Populus deltoides and Populus simonii. We selected a large number of specific RAD tags to construct the linkage map, each of which contained two SNPs, one heterozygous only in the female parent and the other heterozygous only in the male. Consequently, the integrated map contained a total of 1154 RAD tags and 19 linkage groups, with a total length of 5255.49 cM and an average genetic distance of 4.63 cM. Meanwhile, the two parent-specific linkage maps were also constructed with SNPs that were heterozygous in one parent and homozygous in the other. We found that the integrated linkage map was more consensus with the genomic sequences of P. simonii and P. deltoides. Additionally, the likelihood of the marker order in each linkage group of the integrated map was greater than that in both parental maps. The integrated linkage map was more accurate than the parent-specific linkage maps constructed in the same F1 hybrid population, providing a powerful genetic resource for identifying the quantitative trait loci (QTLs) with dominant effects, assembling genomic sequences, and performing comparative genomics in related Populus species. More importantly, this novel strategy can be used in other outbred species to build an integrated linkage map.

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Climate change (CC) is already impacting Arabica coffee cultivation in the intertropical zone. To deal with this situation, it is no longer possible to manage this crop using industrial agriculture techniques, which has been the main strategy implemented since the Green Revolution. Developing a more sustainable agriculture system that respects people and the environment is essential to guarantee future generations' access to natural resources. In the case of Arabica coffee, the solution has been found. Agroforestry is proposed as an ecosystem-based strategy to mitigate and adapt to CC. At least 60% of Arabica coffee is produced in agroforestry systems (AFSs), which are the most sustainable way to produce coffee. Nevertheless, AFS coffee cultivation is currently uncompetitive partly because all modern varieties, selected for full-sun intensive cropping systems, have low yields in shaded environments. Here we review the reasons why agroforestry is part of the solution to CC, and why no breeding work has been undertaken for this cropping system. Based on the literature data, for breeding purposes we also define for the first time one possible coffee ideotype required for AFS coffee cultivation. The four main traits are: (1) productivity based on F1 hybrid vigor, tree volume and flowering intensity under shade; (2) beverage quality by using wild Ethiopian accessions as female progenitors and selecting for this criterion using specific biochemical and molecular predictors; (3) plant health to ensure good tolerance to stress, especially biotic; and (4) low fertilization to promote sustainable production. For each of these traits, numerous criteria with threshold values to be achieved per trait were identified. Through this research, an ecosystem-based breeding strategy was defined to help create new F1 hybrid varieties within the next 10 years.

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Root foraging enables plants to obtain more soil nutrients in a constantly changing nutrient environment. Little is known about the adaptation mechanism of adventitious roots of plants dominated by asexual reproduction (such as tea plants) to soil potassium heterogeneity. We investigated root foraging strategies for K by two tea plants (low-K tolerant genotype "1511" and low-K intolerant genotype "1601") using a multi-layer split-root system. Root exudates, root architecture and transcriptional responses to K heterogeneity were analyzed by HPLC, WinRHIZO and RNA-seq. With the higher leaf K concentrations and K biological utilization indexes, "1511" acclimated to K heterogeneity better than "1601". For "1511", maximum total root length and fine root length proportion appeared on the K-enriched side; the solubilization of soil K reached the maximum on the low-K side, which was consistent with the amount of organic acids released through root exudation. The cellulose decomposition genes that were abundant on the K-enriched side may have promoted root proliferation for "1511". This did not happen in "1601". The low-K tolerant tea genotype "1511" was better at acclimating to K heterogeneity, which was due to a smart root foraging strategy: more roots (especially fine roots) were developed in the K-enriched side; more organic acids were secreted in the low-K side to activate soil K and the root proliferation in the K-enriched side might be due to cellulose decomposition. The present research provides a practical basis for a better understanding of the adaptation strategies of clonal woody plants to soil nutrient availability.

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There has been an increased interest in true potato seeds (TPS) as planting material because of their advantages over seed tubers. TPS produced from a tetraploid heterozygous bi-parental population produces non-uniform segregating progenies, which have had limited uniformity in yield and quality in commercial cultivation, and, thus, limited success. Inbreeding depression and self-incompatibility hamper the development of inbred lines in both tetraploid and diploid potatoes, impeding hybrid development efforts. Diploid potatoes have gametophytic self-incompatibility (SI) controlled by S-locus, harboring the male-dependent S-locus F-box (SLF/SFB) and female-dependent Stylar-RNase (S-RNase). Manipulation of these genes using biotechnological tools may lead to loss of self-incompatibility. Self-compatibility can also be achieved by the introgression of S-locus inhibitor (Sli) found in the self-compatible (SC) natural mutants of Solanum chacoense. The introgression of Sli through conventional breeding methods has gained much success. Recently, the Sli gene has been cloned from diverse SC diploid potato lines. It is expressed gametophytically and can overcome the SI in different diploid potato genotypes through conventional breeding or transgenic approaches. Interestingly, it has a 533 bp insertion in its promoter elements, a MITE transposon, making it a SC allele. Sli gene encodes an F-box protein PP2-B10, which consists of an F-box domain linked to a lectin domain. Interaction studies have revealed that the C-terminal region of Sli interacts with most of the StS-RNases, except StS-RNase 3, 9, 10, and 13, while full-length Sli cannot interact with StS-RNase 3, 9, 11, 13, and 14. Thus, Sli may play an essential role in mediating the interactions between pollen and stigma and function like SLFs to interact with and detoxify the S-RNases during pollen tube elongation to confer SC to SI lines. These advancements have opened new avenues in the diploid potato hybrid.

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Although the crossover (CO) patterns of different species have been extensively investigated, little is known about the landscape of CO patterns in Populus because of its high heterozygosity and long-time generation. A novel strategy was proposed to reveal the difference of CO rate and interference between Populus deltoides and Populus simonii using their F1 hybrid population. We chose restriction site-associated DNA (RAD) tags that contained two SNPs, one only receiving the CO information from the female P. deltoides and the other from the male P. simonii. These RAD tags allowed us to investigate the CO patterns between the two outbred species, instead of using the traditional backcross populations in inbred lines. We found that the CO rate in P. deltoides was generally greater than that in P. simonii, and that the CO interference was a common phenomenon across the two genomes. The COs landscape of the different Populus species facilitates not only to understand the evolutionary mechanism for adaptability but also to rebuild the statistical model for precisely constructing genetic linkage maps that are critical in genome assembly in Populus. Additionally, the novel strategy could be applied in other outbred species for investigating the CO patterns.

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The degree to which male sexual behavior and territorial aggression are regulated by gonadal steroid hormones depends strongly on species and experience. While castration abolishes male sexual behavior in most laboratory rodents, approximately one third of B6D2F1 mice retain the full repertoire of male sexual behaviors long term ("maters"). It is not yet known whether maters retain other behaviors that typically rely on gonadal steroids to a greater extent than non-maters. In this study, we tested aggressive behavior in B6D2F1 males and males of each parental strain (C57BL/6J and DBA/2J) in the resident intruder paradigm before and after castration, as well as male sexual behavior after castration. Before castration, B6D2F1 residents displayed more attacks compared to DBA/2J males (p < 0.05). There was no difference in attack frequency between B6D2F1 and C57BL/6J males nor between DBA/2J and C57BL/6J males (p > 0.2). A greater proportion of hybrid males demonstrated intromissions and the ejaculatory reflex compared to males of either parental strain (p < 0.01). After castration, B6D2F1 residents attacked more than C57BL/6J males, but not DBA/2 J males (p < 0.05; p > 0.2). There was no difference in post-castration attack frequency between maters and non-maters (p > 0.7). Finally, residents that attacked during all 3 pre-castration resident intruder tests displayed more attacks post-castration than animals that attacked during 1 pre-castration test (p < 0.05). These data suggest that strain and experience influence the expression of aggressive behavior after castration and warrant future study in experience-induced transient increases in extragonadal testosterone.

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In rodents, gonadal steroids play a critical yet variable role in behaviors such as social interaction and cognitive performance. Gonadal steroids organize sex differences observed in spatial working memory, while the absence of activational effects induced by castration generally impedes spatial learning and memory. Although male sexual behavior is typically inhibited following castration, a significant proportion of gonadectomized B6D2F1 hybrid males retains the complete repertoire of male reproductive behavior. In a prior study, amyloid precursor protein and tau, proteins involved in cognitive behavior, facilitated steroid-independent male sex behavior in B6D2F1 hybrid male mice. We used this strain to investigate the relationship between gonadal steroid-independent male sexual behavior and cognition. After identifying "maters" (animals retaining steroid-independent male sex behavior) and "non-maters," we tested spatial memory in an 8-arm radial arm maze. Although neither group demonstrated a decrease in errors as a function of time, maters committed fewer errors compared to non-maters overall (p < 0.05). Maters also completed the maze more quickly than non-maters (p < 0.05). We measured mRNA expression of APP and MAPT as well as LEPR and D2R to probe potential roles of metabolism and motivation. Uniquely among maters, increased relative expression of D2R and LEPR in the hippocampus was associated with a longer latency to complete the maze during the last 3 or across all trials, respectively. These data demonstrate that maters outperform non-maters in the radial arm maze, warranting further study of potential differences in acquisition of spatial memory tasks or learning strategy between these groups.

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Introgressive hybridization can pose a serious threat to endangered species which have an overlapping distribution such as in the case of two polecat species, Mustela eversmanii and M. putorius, in Europe. The population size of steppe polecat is known to continuously shrink, whereas its sister species, the European polecat, is still somehow widespread. In this study, we perform an analysis using microsatellite (SSR) and genomic (SNP) data sets to identify natural hybrids between polecats. Four populations were genotyped for eight polymorphic SSR loci, and thousands of unlinked SNPs were generated using a reduced-representation sequencing approach, RADseq, to characterize the genetic make-up of allopatric populations and to identify hybrids in the sympatric area. We applied standard population genetic analyses to characterize the populations based on their SSR allelic frequency. Only a single sample out of 48 sympatric samples showed exact intermediacy that we identified as an F1 hybrid. Additionally, one specimen was indicated in the genomic data sets as backcrossed. Other backcrosses, indicated by SSRs, were not validated by SNPs, which highlights the higher efficacy of the genomic method to identify backcrossed individuals. The low frequency of hybridization suggests that the difference in habitat preference of the two species may act as a barrier to admixture. Therefore, it is apparently unlikely that polecat populations are threatened by significant introgression. The two species showed a clear genetic differentiation using both techniques. We found higher genetic diversity values in the sympatric steppe polecat population than in the other studies on polecat populations. Although M. putorius is a hunted species in most countries, genetic diversity values indicate worse conditions in Europe than in the protected sibling species M. eversmanii. Suspending hunting and providing protected status of the former seems to be reasonable and timely.

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For about a century, plant breeding has widely exploited the heterosis phenomenon-often considered as hybrid vigor-to increase agricultural productivity. The ensuing F1 hybrids can substantially outperform their progenitors due to heterozygous combinations that mitigate deleterious mutations occurring in each genome. However, only fragmented knowledge is available concerning the underlying genes and processes that foster heterosis. Although cotton is among the highly valued crops, its improvement programs that involve the exploitation of heterosis are still limited in terms of significant accomplishments to make it broadly applicable in different agro-ecological zones. Here, F1 hybrids were derived from mating a diverse Upland Cotton germplasm with commercially valuable cultivars in the Line × Tester fashion and evaluated across multiple environments for 10 measurable traits. These traits were dissected into five different heterosis types and specific combining ability (SCA). Subsequent genome-wide predictions along-with association analyses uncovered a set of 298 highly significant key single nucleotide polymorphisms (SNPs)/Quantitative Trait Nucleotides (QTNs) and 271 heterotic Quantitative Trait Nucleotides (hQTNs) related to agronomic and fiber quality traits. The integration of a genome wide association study with RNA-sequence analysis yielded 275 candidate genes in the vicinity of key SNPs/QTNs. Fiber micronaire (MIC) and lint percentage (LP) had the maximum number of associated genes, i.e., each with 45 related to QTNs/hQTNs. A total of 54 putative candidate genes were identified in association with HETEROSIS of quoted traits. The novel players in the heterosis mechanism highlighted in this study may prove to be scientifically and biologically important for cotton biologists, and for those breeders engaged in cotton fiber and yield improvement programs.

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To date, natural resistance or tolerance, which can be introduced into crops by crossing, to potato spindle tuber viroid (PSTVd) has not been reported. Additionally, responses to PSTVd infection in many wild tomato species, including some species that can be crossed with PSTVd-susceptible cultivated tomatoes (Solanum lycopersicum var. lycoperaicum), have not been ascertained. The aim of this study was to evaluate responses to PSTVd infection including resistance and tolerance. Accordingly, we inoculated several cultivated and wild tomato species with intermediate and lethal strains of PSTVd. None of the host plants exhibited sufficient resistance to PSTVd to render systemic infection impossible; however, these plants displayed other responses, including tolerance. Further analysis of PSTVd accumulation revealed low accumulation of PSTVd in two wild species, exhibiting high tolerance, even to the lethal strain. Additionally, F1 hybrids generated by crossing a PSTVd-sensitive wild tomato (Solanum lycopersicum var. cerasiforme) with these wild relatives also exhibited tolerance to the lethal PSTVd strain, which is accompanied by low PSTVd accumulation during early infection. These results indicate that the tolerance toward PSTVd in wild species is a dominant trait and can be utilized for tomato breeding by crossing.

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Cultivated strawberry is the most widely consumed fruit crop in the world, and therefore, many breeding programs are underway to improve its agronomic traits such as fruit quality. Strawberry cultivars were vegetatively propagated through runners and carried a high risk of infection with viruses and insects. To solve this problem, the development of F1 hybrid seeds has been proposed as an alternative breeding strategy in strawberry. In this study, we conducted a potential assessment of genomic selection (GS) in strawberry F1 hybrid breeding. A total of 105 inbred lines were developed as candidate parents of strawberry F1 hybrids. In addition, 275 parental combinations were randomly selected from the 105 inbred lines and crossed to develop test F1 hybrids for GS model training. These populations were phenotyped for petiole length, leaf area, Brix, fruit hardness, and pericarp color. Whole-genome shotgun sequencing of the 105 inbred lines detected 20,811 single nucleotide polymorphism sites that were provided for subsequent GS analyses. In a GS model construction, inclusion of dominant effects showed a slight advantage in GS accuracy. In the across population prediction analysis, GS models using the inbred lines showed predictability for the test F1 hybrids and vice versa, except for Brix. Finally, the GS models were used for phenotype prediction of 5,460 possible F1 hybrids from 105 inbred lines to select F1 hybrids with high fruit hardness or high pericarp color. These F1 hybrids were developed and phenotyped to evaluate the efficacy of the GS. As expected, F1 hybrids that were predicted to have high fruit hardness or high pericarp color expressed higher observed phenotypic values than the F1 hybrids that were selected for other objectives. Through the analyses in this study, we demonstrated that GS can be applied for strawberry F1 hybrid breeding.

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BACKGROUND: Self-incompatibility (SI) systems prevent self-fertilization in several species of Poaceae, many of which are economically important forage, bioenergy and turf grasses. Self-incompatibility ensures cross-pollination and genetic diversity but restricts the ability to fix useful genetic variation. In most inbred crops it is possible to develop high-performing homozygous parental lines by self-pollination, which then enables the creation of F1 hybrid varieties with higher performance, a phenomenon known as heterosis. The inability to fully exploit heterosis in outcrossing grasses is partially responsible for lower levels of improvement in breeding programmes compared with inbred crops. However, SI can be overcome in forage grasses to create self-compatible populations. This is generating interest in understanding the genetical basis of self-compatibility (SC), its significance for reproductive strategies and its exploitation for crop improvement, especially in the context of F1 hybrid breeding. SCOPE: We review the literature on SI and SC in outcrossing grass species. We review the currently available genomic tools and approaches used to discover and characterize novel SC sources. We discuss opportunities barely explored for outcrossing grasses that SC facilitates. Specifically, we discuss strategies for wide SC introgression in the context of the Lolium-Festuca complex and the use of SC to develop immortalized mapping populations for the dissection of a wide range of agronomically important traits. The germplasm available is a valuable practical resource and will aid understanding the basis of inbreeding depression and hybrid vigour in key temperate forage grass species. CONCLUSIONS: A better understanding of the genetic control of additional SC loci offers new insight into SI systems, their evolutionary origins and their reproductive significance. Heterozygous outcrossing grass species that can be readily selfed facilitate studies of heterosis. Moreover, SC introduction into a range of grass species will enable heterosis to be exploited in innovative ways in genetic improvement programmes.

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Heterosis is a phenomenon wherein F1 hybrid often displays phenotypic superiority and surpasses its parents in terms of growth and agronomic traits. Investigations on the physiological and biochemical properties of the heterotic F1 hybrid are important to uncover the mechanisms underlying heterosis in plants. In the present study, the photosynthetic capacity of a heterotic F1 hybrid of Zea mays L. (DHM 117) that exhibited a higher growth rate and increased biomass was compared with its parental inbreds at vegetative and reproductive stages in the field during 2017 and 2018. The net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E) as well as foliar carbohydrates were higher in F1 hybrid than parental inbreds at vegetative and reproductive stages. An increase in total chlorophyll content along with better chlorophyll a fluorescence characteristics including effective quantum yield of photosystem II (ΔF/Fm'), maximum quantum yield of PSII (Fv/Fm), photochemical quenching (qp) and decreased non-photochemical quenching (NPQ) was observed in F1 hybrid than the parental inbreds. Further, the expression of potential genes related to C4 photosynthesis was considerably upregulated in F1 hybrid than the parental inbreds during vegetative and reproductive stages. Moreover, the F1 hybrid exhibited distinct heterosis in yield with 63% and 62% increase relative to parental inbreds during 2017 and 2018. We conclude that improved photosynthetic efficiency associated with increased foliar carbohydrates could have contributed to higher growth rate, biomass and yield in the F1 hybrid.

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