Backcross Families Research Articles

Molecular Characterisation of a Supergene Conditioning Super-High Vitamin C in Kiwifruit Hybrids.

During analysis of kiwifruit derived from hybrids between the high vitamin C (ascorbic acid; AsA) species Actinidia eriantha and A. chinensis, we observed bimodal segregation of fruit AsA concentration suggesting major gene segregation. To test this hypothesis, we performed whole-genome sequencing on pools of hybrid genotypes with either high or low AsA fruit. Pool-GWAS (genome-wide association study) revealed a single Quantitative Trait Locus (QTL) spanning more than 5 Mbp on chromosome 26, which we denote as qAsA26.1. A co-dominant PCR marker was used to validate this association in four diploid (A. chinensis × A. eriantha) × A. chinensis backcross families, showing that the A. eriantha allele at this locus increases fruit AsA levels by 250 mg/100 g fresh weight. Inspection of genome composition and recombination in other A. chinensis genetic maps confirmed that the qAsA26.1 region bears hallmarks of suppressed recombination. The molecular fingerprint of this locus was examined in leaves of backcross validation families by RNA sequencing (RNASEQ). This confirmed strong allelic expression bias across this region as well as differential expression of transcripts on other chromosomes. This evidence suggests that the region harbouring qAsA26.1 constitutes a supergene, which may condition multiple pleiotropic effects on metabolism.

Dissecting Resistance to Phytophthora cinnamomi in Interspecific Hybrid Chestnut Crosses Using Sequence-Based Genotyping and QTL Mapping

The soilborne oomycete Phytophthora cinnamomi-which causes root rot, trunk cankers, and stem lesions on an estimated 5,000 plant species worldwide-is a lethal pathogen of American chestnut (Castanea dentata) as well as many other woody plant species. P. cinnamomi is particularly damaging to chestnut and chinquapin trees (Castanea spp.) in the southern portion of its native range in the United States due to relatively mild climatic conditions that are conductive to disease development. Introduction of resistant genotypes is the most practical solution for disease management in forests because treatment with fungicides and eradication of the pathogen are neither practical nor economically feasible in natural ecosystems. Using backcross families derived from crosses of American chestnuts with two resistant Chinese chestnut cultivars Mahogany and Nanking, we constructed linkage maps and identified quantitative trait loci (QTLs) for resistance to P. cinnamomi that had been introgressed from these Chinese chestnut cultivars. In total, 957 plants representing five cohorts of three hybrid crosses were genotyped by sequencing and phenotyped by standardized inoculation and visual examination over a 6-year period from 2011 to 2016. Eight parental linkage maps comprising 7,715 markers were constructed, and 17 QTLs were identified on four linkage groups (LGs): LG_A, LG_C, LG_E, and LG_K. The most consistent QTLs were detected on LG_E in seedlings from crosses with both 'Mahogany' and 'Nanking' and LG_K in seedlings from 'Mahogany' crosses. Two consistent large and medium effect QTLs located ∼10 cM apart were present in the middle and at the lower end of LG_E; other QTLs were considered to have small effects. These results imply that the genetic architecture of resistance to P. cinnamomi in Chinese chestnut × American chestnut hybrid progeny may resemble the P. sojae-soybean pathosystem, with a few dominant QTLs along with quantitatively inherited partial resistance conferred by multiple small-effect QTLs.

Identifying Host Resistance to Phytophthora cinnamomi in Hybrid Progeny of Castanea dentata and Castanea mollissima

Phytophthora cinnamomi Rands, the causal pathogen of phytophthora root rot (PRR) of chestnut, is one of the main obstacles to growth of american chestnut [Castanea dentata (Marsh.) Bork.] in the southern part of its distribution. To facilitate introgression of PRR resistance of chinese chestnut (C. mollissima Blume) into a C. dentata genetic background, we assessed the disease resistance of 10 interspecific hybrid families derived from potentially resistant C. mollissima cultivars. Hybrid progeny were inoculated with P. cinnamomi in the nursery and assessed for root lesion severity after 1 year of growth. Asymptomatic plants were transplanted to a P. cinnamomi-positive orchard and evaluated for survival midway through the following growing season. During the nursery experiment, 8 of 10 hybrid families were not significantly different from susceptible C. dentata controls for average disease resistance scores. However, multiple asymptomatic individuals were identified in each of the eight families. Two of the 10 hybrid families were not significantly different from the resistant C. mollissima and C. henryi controls. In the P. cinnamomi-positive orchard, the prescreened hybrid families displayed a greater proportion of survivors than backcross families that had not been prescreened for P. cinnamomi resistance. Hybrid plants that have survived 2 years of growth in P. cinnamomi-infested potting media and soils represent an important step toward the production of genetically diverse chestnut populations in the southeastern United States that combine the PRR resistance of C. mollissima with the morphology and local adaptation of C. dentata.

Maintaining product quality in raisins throughout the introgression of powdery mildew resistance

ABSTRACT The availability of powdery mildew-resistant raisin accessions will lower grower production costs and enhance the environment through reduced fungicide use. To achieve this objective, backcrossing has been employed with Vitis romanetii as the source of non-race-specific powdery mildew resistance. Initial crosses of powdery mildew-resistant F1 hybrid B36-45 with seeded raisin cultivars ‘Rangspray’ and ‘Raisin de Palestine’ yielded seedless powdery mildew-resistant first-generation backcross selections C87-41 and C87-106, which were used to develop second-generation backcross populations. Principal component analyses consistently identified ‘wrinkle,’ ‘meatiness,’ ‘product attractiveness’ and ‘skin persistence’ as being the quality characteristics most important in discriminating among powdery mildew-resistant raisin accessions and commercial raisin cultivars. Raisin quality ratings were much improved across most evaluated characters in second-generation backcross families as compared with parental powdery mildew- resistant accessions C87-41 and C87-106. After two generations of backcrossing, powdery mildew-resistant raisin selections were identified with product quality characteristics similar to those of commercial raisin cultivars.

Restricted glyphosate translocation in Lolium multiflorum is controlled by a single incomplete dominant nuclear gene

ABSTRACTThe mode of inheritance for herbicide resistance was investigated in a population of Lolium multiflorum (Italian ryegrass) with restricted glyphosate translocation mechanism of resistance. The degree of dominance for glyphosate resistance in Italian ryegrass was evaluated in the progenies of F1 families which were created by reciprocal-crossing between resistant (R) and susceptible (S) parental individuals. The results showed an intermediate level of glyphosate resistance for F1 families compared to that of the parental types. The phenotypic resistance segregation was also investigated using backcross families which were created by pair-crossing the F1 individuals to the susceptible population, and the observed segregation values fitted a one-gene model very well. Thus it appears that glyphosate resistance in the Italian ryegrass obtained from a New Zealand vineyard with restricted herbicide translocation is controlled by a single incompletely dominant nuclear gene.

Mapping of quantitative trait loci associated with size, shape, and parr mark traits using first- and second-generation backcrosses between European and North American Atlantic salmon (Salmo salar).

Little is known about the genetic architecture of traits important for salmonid restoration ecology. We mapped quantitative trait loci (QTL) using single nucleotide polymorphisms (SNPs) for juvenile body length, weight, shape, and vertical skin pigmentation patterns (parr marks) within three hybrid backcross families between European and North American subspecies of Atlantic salmon. Amounts of variation in skin colour and pattern quantified in the two second-generation transAtlantic families exceeded the ranges seen in purebred populations. GridQTL analyses using low-density female-specific linkage maps detected QTL showing experiment-wide significance on Ssa02, Ssa03, Ssa09, Ssa11, Ssa19, and Ssa26/28 for both length and weight; on Ssa04 and Ssa23 for parr mark number; on Ssa09 and Ssa13 for parr mark contrast; and on Ssa05, Ssa07, Ssa10, Ssa11, Ssa18, Ssa23, and Ssa26/28 for geometric morphometric shape coordinates. Pleiotrophic QTL on Ssa11 affected length, weight, and shape. No QTL was found that explained more than 10% of the phenotypic variance in pigmentation or shape traits. Each QTL was approximately positioned on the physical map of the Atlantic salmon genome. Some QTL locations confirmed previous studies but many were new. Studies like ours may increase the success of salmon restoration projects by enabling better phenotypic and genetic matching between introduced and extirpated strains.

Gibberellins Promote Brassinosteroids Action and Both Increase Heterosis for Plant Height in Maize (Zea mays L.).

Brassinosteroids (BRs) and Gibberellins (GAs) are two classes of plant hormones affecting plant height (PHT). Thus, manipulation of BR and GA levels or signaling enables optimization of crop grain and biomass yields. We established backcross (BC) families, selected for increased PHT, in two elite maize inbred backgrounds. Various exotic accessions used in the germplasm enhancement in maize project served as donors. BC1-derived doubled haploid lines in the same two elite maize inbred backgrounds established without selection for plant height were included for comparison. We conducted genome-wide association studies to explore the genetic control of PHT by BR and GA. In addition, we used BR and GA inhibitors to compare the relationship between PHT, BR, and GA in inbred lines and heterozygotes from a physiological and biological perspective. A total of 73 genomic loci were discovered to be associated with PHT, with seven co-localized with GA, and two co-localized with BR candidate genes. PHT determined in field trials was significantly correlated with seedling stage BR and GA inhibitor responses. However, this observation was only true for maize heterozygotes, not for inbred lines. Path analysis results suggest that heterozygosity increases GA levels, which in turn promote BR levels. Thus, at least part of heterosis for PHT in maize can be explained by increased GA and BR levels, and seedling stage hormone inhibitor response is promising to predict heterosis for PHT.

The rough fur (ruf) mutation in mice is an allele of myelin protein zero-like 3 (Mpzl3)

Background: The recessive rough fur mutation ( ruf )―named for the unkempt, greasy appearance of the hair coat in homozygotes―has previously been mapped on mouse Chromosome 9. However, the assignment of ruf to a particular gene is needed to facilitate a complete molecular analysis of the mutant phenotype. Results: To establish a more refined location for ruf (as a basis for positional cloning) DNA isolated from a large backcross family was typed for microsatellite and single-nucleotide markers on Chromosome 9. This analysis restricted the location of ruf between sites that flank only four genes known to be expressed in skin, one of which― Mpzl3 , for myelin protein zero-like 3―generates a similar hair phenotype in mice homozygous for engineered and spontaneous null-alleles. A cross between ruf mutants and mice heterozygous for the Mpzl3 rc mutation (which controls a recessive phenotype called rough coat) produced offspring that displayed matted, damp-looking fur, indicating that ruf is a mutant allele of Mpzl3 . However, sequence analysis of the Mpzl3 promoter, exons and splice junctions revealed no mutant-specific DNA defect. Conclusion: The results presented indicate that ruf is a mutant allele of Mpzl3 . With a genetic assignment in hand, the rough fur variant can now be more fully characterized to advance our understanding of Mpzl3 ’s role in normal skin development and function, hepatic triglyceride synthesis, weight regulation, energy and glucose homeostasis; and to model-related human disorders.

Inheritance and allelism of morphological traits in eastern redbud (Cercis canadensis L.).

Inheritance of purple, gold, and variegated foliage types, weeping architecture, and double flower was explored in F1, F2, and backcross families resulting from controlled hybridization of eastern redbud (Cercis canadensis L.). Potential allelic relationships were explored when possible. Inheritance analysis in families derived from controlled hybridization of ‘Covey’ (green leaf) and ‘Forest Pansy’ (purple leaf) suggest that purple leaf color and weeping architecture are both controlled by single recessive genes, for which the symbols pl1 and wp1 are proposed, respectively. Inheritance of gold leaf was explored in families of ‘Covey’ (green leaf) × ‘Hearts of Gold’ (gold leaf). Interpretation of inheritance of gold leaf in these families was confounded by the recovery of a leaf color phenotype in the F2 family unlike either parent. However, data suggested the action of a single locus controlling gold leaf color in ‘Hearts of Gold’, and that instability of gold leaf expression may be based on transposable element activity. Segregation of gold leaf in the F2 families of ‘Texas White’ [green leaf (C. canadensis var. texensis)] × ‘JN2’ [gold leaf (The Rising Sun)] did not fit a Mendelian ratio. Analysis of progeny of ‘Silver Cloud’ and ‘Floating Clouds’ (both showing white/green leaf variegation) with non-variegated cultivars demonstrated that variegation in ‘Silver Cloud’ is controlled by a single recessive nuclear gene, while variegation in ‘Floating Clouds’ is controlled by cytoplasmic factors. The symbol var1 is proposed for the gene controlling variegation in ‘Silver Cloud’. Double flower in progeny derived from ‘Flame’ (double flower) suggested that double flower is dominant to single flower, and that ‘Flame’ is heterozygous at the double-flower locus, for which the symbol Df1 is proposed. Allelism studies showed that the gene controlling purple leaf in ‘Forest Pansy’ is allelic to the purple leaf gene in ‘Greswan’ and that the gene controlling weeping phenotype in ‘Traveller’ (C. canadensis var. texensis) is non-allelic to the weeping gene found in ‘Covey’. Allelism of the gold leaf trait in ‘Hearts of Gold’ and ‘JN2’ was investigated, but no clear conclusions regarding allelism could be made due to recovery of leaf color phenotypes unlike either parent.

Mapping QTL for Resistance Against Viral Nervous Necrosis Disease in Asian Seabass.

Viral nervous necrosis disease (VNN), caused by nervous necrosis virus (NNV), leads to mass mortality in mariculture. However, phenotypic selection for resistance against VNN is very difficult. To facilitate marker-assisted selection (MAS) for resistance against VNN and understanding of the genetic architecture underlying the resistance against this disease, we mapped quantitative trait loci (QTL) for resistance against VNN in Asian seabass. We challenged fingerlings at 37 days post-hatching (dph), from a single back-cross family, with NNV at a concentration of 9 × 10(6) TCID50/ml for 2 h. Daily mortalities were recorded and collected. A panel of 330 mortalities and 190 surviving fingerlings was genotyped using 149 microsatellites with 145 successfully mapped markers covering 24 linkage groups (LGs). Analysis of QTL for both resistance against VNN and survival time was conducted using interval mapping. Five significant QTL located in four LGs and eight suggestive QTL in seven LGs were identified for resistance. Another five significant QTL in three LGs and five suggestive QTL in three LGs were detected for survival time. One significant QTL, spanning 3 cM in LG20, was identified for both resistance and survival time. These QTL explained 2.2-4.1% of the phenotypic variance for resistance and 2.2-3.3% of the phenotypic variance for survival time, respectively. Our results suggest that VNN resistance in Asian seabass is controlled by many loci with small effects. Our data provide information for fine mapping of QTL and identification of candidate genes for a better understanding of the mechanism of disease resistance.

Identification of suitable segregating SSR markers for blast resistance in rice using inheritance and disease reaction analysis in backcross families

The study was conducted to identify the suitable SSR markers in relation to blast disease of rice. Backcross breeding was applied and BC2F1 generation was produced using rice variety Pongsu Seribu 2 as blast resistant parent and MR219 as susceptible parent. Eleven SSR markers related to blast resistance genes (Pi gene) were found highly polymorphic between the parental lines. According to single-gene model only two markers, RM208 and RM206, fitted to the expected test cross ratio (1:1) in BC2F1 generation with the relation to resistant and susceptible plants. Further BC2F1 population carrying 320 plants were inoculated with the highly virulent pathotype P7.2 of Magnaporthe oryze. Chi-square (χ2) test for single-gene model showed goodness of fit (p = 0.45) to the expected segregation ratio (1:1) for phenotypic segregation in BC2F1 population. In marker segregation analysis two markers RM208 (χ2 = 1.513, p = 0.218) and RM206 (χ2 = 0.613, P = 0.433) clearly produced goodness of fit to the expected test cross ratio (1:1) for the single-gene model. The present finding could help the rice breeders to monitor the blast resistance genes with appropriate and highly segregating SSR markers in rice varietal development program against blast disease.

The mouse wellhaarig (we) mutations result from defects in epidermal-type transglutaminase 3 (Tgm3).

The recessive wellhaarig (we) mutations, named for the wavy coat and curly whiskers they generate in homozygotes, have previously been mapped on mouse Chromosome 2. To further limit the possible location of the we locus, we crossed hybrid (C57BL/6×AKR)F1, we(4J)/+ females with AKR, we(4J)/we(4J) mutant males to create a large backcross family that was typed for various microsatellite markers and single-nucleotide polymorphisms (SNPs) that distinguish strains AKR and B6. This analysis restricted the location of we(4J) between sites that flank only one gene known to be expressed in skin: epidermal-type transglutaminase 3 (Tgm3). To test Tgm3 as a candidate for the basis of the wellhaarig phenotype we took two approaches. First, we sequenced all Tgm3 coding regions in mice homozygous for four independent, naturally-occurring wellhaarig alleles (we, we(Bkr), we(3J) and we(4J)) and found distinct defects in three of these mutants. Second, we crossed mice homozygous for an induced mutant allele of Tgm3 (Tgm3(Btlr)) with mice heterozygous for one of the wellhaarig alleles we possess (we(4J) or we(Bkr)) to test for complementation. Because the progeny inheriting both a recessive we allele and a recessive Tgm3(Btlr) allele displayed wavy hair, we conclude that the classic wellhaarig mutations result from defects in Tgm3.

Genetic Linkage Maps and Homology Study of Backcross Families of German Faba Bean (Vicia faba L.)

Genetic linkage maps are deployed to locate quantitative trait loci (QTL) of traits of interest and speed up breeding programs. In this study, we used two Vicia faba L. backcross families (BCFams). Genetic linkage maps were constructed with 193 and 288 polymorphic amplified fragment length polymorphism (AFLP) markers using 131 and 132 individuals for BCFam1 and BCFam2, respectively. The BCFam1 linkage map consisted of 18 linkage groups (LGs) encompassing1134.7 cM, with a mean inter-marker distance of 11.94 cM. The BCFam.2 linkage map consisted of 19 LGs encompassing1235 cM with a mean inter-marker distance of 9.29 cM. A set of 13 AFLP markers was homologous among maps of BCFam1 and BCFam2 as well as faba bean consensus map. These linkage maps will be beneficial for genetic analyses and diversity studies as well as for comparative mapping of faba bean and related species.

RAD-QTL Mapping Reveals Both Genome-Level Parallelism and Different Genetic Architecture Underlying the Evolution of Body Shape in Lake Whitefish (Coregonus clupeaformis) Species Pairs.

Parallel changes in body shape may evolve in response to similar environmental conditions, but whether such parallel phenotypic changes share a common genetic basis is still debated. The goal of this study was to assess whether parallel phenotypic changes could be explained by genetic parallelism, multiple genetic routes, or both. We first provide evidence for parallelism in fish shape by using geometric morphometrics among 300 fish representing five species pairs of Lake Whitefish. Using a genetic map comprising 3438 restriction site−associated DNA sequencing single-nucleotide polymorphisms, we then identified quantitative trait loci underlying body shape traits in a backcross family reared in the laboratory. A total of 138 body shape quantitative trait loci were identified in this cross, thus revealing a highly polygenic architecture of body shape in Lake Whitefish. Third, we tested for evidence of genetic parallelism among independent wild populations using both a single-locus method (outlier analysis) and a polygenic approach (analysis of covariation among markers). The single-locus approach provided limited evidence for genetic parallelism. However, the polygenic analysis revealed genetic parallelism for three of the five lakes, which differed from the two other lakes. These results provide evidence for both genetic parallelism and multiple genetic routes underlying parallel phenotypic evolution in fish shape among populations occupying similar ecological niches.

The effect of Bt-transgene introgression on plant growth and reproduction in wild Brassica juncea.

This study aims to investigate the relative plant growth and reproduction of insect-resistant and susceptible plants following the introgression of an insect-resistance Bt-transgene from Brassica napus, oilseed rape, to wild Brassica juncea. The second backcrossed generation (BC2) from a single backcross family was grown in pure and mixed stands of Bt-transgenic and non-transgenic siblings under two insect treatments. Various proportions of Bt-transgenic plants were employed in mixed stands to study the interaction between resistant and susceptible plants. In the pure stands, Bt-transgenic BC2 plants performed better than non-transgenic plants with or without insect treatments. In mixed stands, Bt-transgenic BC2 plants produced fewer seeds than their non-Bt counterparts at low proportions of Bt-transgenic BC2 plants in the absence of insects. Reproductive allocation of non-transgenic plants marginally increased with increasing proportions of Bt-transgenic plants under herbivore pressure, which resulted in increased total biomass and seed production per stand. The results showed that the growth of non-transgenic plants was protected by Bt-transgenic plants under herbivore pressure. The Bt-transgene might not be advantageous in mixed stands of backcrossed hybrids; thus transgene introgression would not be facilitated when herbivorous insects are not present. However, a relatively large initial population of Bt-transgenic plants might result in transgene persistence when target herbivores are present.

DEVELOPMENT OF TABLE AND RAISIN GRAPES WITH HIGH ANTHOCYANINS USING A LEAF DISK ASSAY

Anthocyanins are considered an excellent source of antioxidant phytochemicals for health benefits. The majority of wine, table and raisin grapes have anthocyanins only in their colored skin. Anthocyanin content of grapes would be increased if their flesh also contained anthocyanins. C33-30, a seedless female flowered table grape with red skin and clear flesh berries was hybridized with the ?Rubired? wine grape, which has black skin and red flesh berries. The F1 progeny segregated in a 3 colored:1 white skin and 1 red:1 clear flesh ratio for colored berries. The seedling expressing the highest level of anthocyanin in the flesh and skin was similar to ?Rubired?. Seven modified backcross families were created by crossing red flesh seeded F1 selections with seedless red skin table or white skin raisin grapes. Skin color segregated as a single dominant gene as expected. One red flesh parent was heterozygous for skin color and the rest were homozygous. Only seedlings with colored skin had red flesh. Flesh color segregated as a 1 red:1 clear in three of the families or in a 2:1 ratio or higher in four families. One red flesh parent produced an abnormally high percentage (>80%) of red flesh seedlings. Leaf color in the leaf disk assay correlated well with flesh color in the F1 family. Seedlings that developed 0 to 20% anthocyanin in the leaf disk assay had clear flesh with white, red or black skin (32% of BC1 population). However 19% of red flesh seedlings would have been discarded using this selection criterion. Part of this discrepancy is due to the fact that leaves taken too early in their development from greenhouse grown plants did not develop anthocyanin.

GENETIC AND GENOMIC RESOURCES FOR MAPPING RESISTANCE TO PHYTOPHTHORA CINNAMOMI IN CHESTNUT

Root rot (caused by Phytophthora cinnamomi) and chestnut blight (caused by Cryphonectria parasitica) are the two most destructive diseases affecting American chestnut, Castanea dentate. Therefore, breeding for resistance to both pathogens simultaneously is essential before the American chestnut can be restored to its full native range. Using combined genetic and genomic approaches, resistance to C. parasitica (Cp) has been mapped to three quantitative trait loci (QTLs) in chestnut. In addition, a marker set covering the chestnut genome has been generated for implementation in breeding for Cp resistance. Although P. cinnamomi was introduced to the USA far earlier than C. parasitica, an effort to breed for resistance to this pathogen has been initiated only recently. Selection of parental genotypes with a high inter-generational transmission rate of resistance to P. cinnamomi (Pc) allowed initiation of genetic studies. In pilot experiments with a limited number of progeny derived from AdairKY1 × GL158, a QTL for resistance (source Chinese chestnut, C. mollissima ‘Nanking’) to Pc was mapped to linkage group E (LG_E). Subsequently, three backcross families (HB1, HB2, and MK5) were selected from another source of resistance (C. mollissima ‘Mahogany’) for map construction and association analysis with 22 markers from LG_E. Our preliminary analyses confirmed the presence of a Pc resistance QTL on LG_E. In 2012, extended mapping populations (up to 200 individuals) representing the Mahogany and Nanking lineages of resistance were planted for phenotyping of Pc resistance and QTL mapping. Together, these materials and analyses should help resolve the location of the QTLs for resistance to Pc and test their co-location between two important sources of resistance in chestnut.

Development of the catfish 250K SNP array for genome-wide association studies

BackgroundQuantitative traits, such as disease resistance, are most often controlled by a set of genes involving a complex array of regulation. The dissection of genetic basis of quantitative traits requires large numbers of genetic markers with good genome coverage. The application of next-generation sequencing technologies has allowed discovery of over eight million SNPs in catfish, but the challenge remains as to how to efficiently and economically use such SNP resources for genetic analysis.ResultsIn this work, we developed a catfish 250K SNP array using Affymetrix Axiom genotyping technology. The SNPs were obtained from multiple sources including gene-associated SNPs, anonymous genomic SNPs, and inter-specific SNPs. A set of 640K high-quality SNPs obtained following specific requirements of array design were submitted. A panel of 250,113 SNPs was finalized for inclusion on the array. The performance evaluated by genotyping individuals from wild populations and backcross families suggested the good utility of the catfish 250K SNP array.ConclusionsThis is the first high-density SNP array for catfish. The array should be a valuable resource for genome-wide association studies (GWAS), fine QTL mapping, high-density linkage map construction, haplotype analysis, and whole genome-based selection.

Mapping quantitative trait loci (QTL) for body weight, length and condition factor traits in backcross (BC1) family of Common carp (Cyprinus carpio L.)

Body weight and length are economical important traits in aquaculture species influenced by quantitative trait loci (QTL) and environmental factors. In this study, a backcross (BC1) common carp family, with 86 progeny, was utilized to construct genetic map for preliminary QTL mapping. The genetic map was constructed with 366 markers, including 191 SNP from gene, coverage 50 linkage groups with an average marker distance of 18.5cM. A total of fourteen QTLs associated with body weight (BW), body length (BL) and condition factor (K) were detected on ten linkage groups (LGs). Among these QTLs detected, three (qBW8, qBL8 and qK8) were associated with BW, BL and K respectively, were mapped on LG8. qBW8 and qK8 were identified on similar interval neared locus HLJ2394 explained 14.9 and 20.9% of the phenotype variance, while qBL8 was identified on separate nearby locus HLJ571 with 30.8% of phenotype variance. Two QTLs, qBW13 and qK13, related with BW and K separately, were found on LG13 at different locus with phenotype variance of 25.3 and 20.9%. Other two QTLs, qBW19 and qBL19, associated to BW and BL were mapped on same region near SNP0626 on LG19, and explained 10.3 and 15.6% of phenotype variance. While other seven QTLs related with BW and BL were located on different LGs. Confidential interval was ranged from 1.1 to 10cM in the present study. These markers, with lower QTL interval, have great influence on the body weight and length. Therefore, these QTLs will be helpful to find out the genes related with specific trait.

Inheritance of evolved resistance to a novel herbicide (pyroxasulfone)

Agricultural weeds have rapidly adapted to intensive herbicide selection and resistance to herbicides has evolved within ecological timescales. Yet, the genetic basis of broad-spectrum generalist herbicide resistance is largely unknown. This study aims to determine the genetic control of non-target-site herbicide resistance trait(s) that rapidly evolved under recurrent selection of the novel lipid biosynthesis inhibitor pyroxasulfone in Lolium rigidum. The phenotypic segregation of pyroxasulfone resistance in parental, F1 and back-cross (BC) families was assessed in plants exposed to a gradient of pyroxasulfone doses. The inheritance of resistance to chemically dissimilar herbicides (cross-resistance) was also evaluated. Evolved resistance to the novel selective agent (pyroxasulfone) is explained by Mendelian segregation of one semi-dominant allele incrementally herbicide-selected at higher frequency in the progeny. In BC families, cross-resistance is conferred by an incompletely dominant single major locus. This study confirms that herbicide resistance can rapidly evolve to any novel selective herbicide agents by continuous and repeated herbicide use. The results imply that the combination of herbicide options (rotation, mixtures or combinations) to exploit incomplete dominance can provide acceptable control of broad-spectrum generalist resistance-endowing monogenic traits. Herbicide diversity within a set of integrated management tactics can be one important component to reduce the herbicide selection intensity.