Recombinant Inbred Population Research Articles

Physical seed dormancy in pea is genetically separable from seed coat thickness and roughness.

The seeds of wild pea (Pisum) exhibit marked physical dormancy due to impermeability of the seed coat to water, and the loss of this dormancy is thought to have been critical for domestication. Wild pea seed coats are also notably thick and rough, traits that have also reduced during domestication and are anecdotally linked to increased permeability. However, how these traits specifically interact with permeability is unclear. To investigate this, we examined the genetic control of differences in seed coat characteristics between wild P. sativum ssp. humile and a non-dormant domesticated P. s. sativum accession in a recombinant inbred population. QTL effects were confirmed and their locations refined in segregating F4/5 populations. In this population we found a moderate correlation between testa thickness and permeability, and identified loci that affect them independently, suggesting no close functional association. However, the major loci affecting both testa thickness and permeability collocated closely with Mendel's pigmentation locus A, suggesting flavonoid compounds under its control might contribute significantly to both traits. We also show that seed coat roughness is oligogenic in this population, with the major locus independent of both testa thickness and permeability, suggesting selection for smooth seed was unlikely to be due to effects on either of these traits. Results indicate loss of seed coat dormancy during domestication was not primarily driven by reduced testa thickness or smooth seededness. The close association between major permeability and thickness QTL and Mendel's 'A' warrant further study, particularly regarding the role of flavonoids.

TEAD1, MYO7A and NDUFC2 are novel functional genes associated with glucose metabolism in BXD recombinant inbred population.

The liver is an important metabolic organ that governs glucolipid metabolism, and its dysfunction may cause non-alcoholic fatty liver disease, type 2 diabetes mellitus, dyslipidaemia, etc. We aimed to systematic investigate the key factors related to hepatic glucose metabolism, which may be beneficial for understanding the underlying pathogenic mechanisms for obesity and diabetes mellitus. Oral glucose tolerance test (OGTT) phenotypes and liver transcriptomes of BXD mice under chow and high-fat diet conditions were collected from GeneNetwork. QTL mapping was conducted to pinpoint genomic regions associated with glucose homeostasis. Candidate genes were further nominated using a multi-criteria approach and validated to confirm their functional relevance in vitro. Our results demonstrated that plasma glucose levels in OGTT were significantly affected by both diet and genetic background, with six genetic regulating loci were mapped on chromosomes 1, 4, and 7. Moreover, TEAD1, MYO7A and NDUFC2 were identified as the candidate genes. Functionally, siRNA-mediated TEAD1, MYO7A and NDUFC2 knockdown significantly decreased the glucose uptake and inhibited the transcription of genes related to insulin and glucose metabolism pathways. Our study contributes novel insights to the understanding of hepatic glucose metabolism, demonstrating the impact of TEAD1, MYO7A and NDUFC2 on mitochondrial function in the liver and their regulatory role in maintaining in glucose homeostasis.

Genetic Mapping and Characterization of Verticillium Wilt Resistance in a Recombinant Inbred Population of Upland Cotton.

Verticillium wilt (VW) is an important and widespread disease of cotton and once established is long-lived and difficult to manage. In Australia, the non-defoliating pathotype of Verticillium dahliae is the most common, and extremely virulent. Breeding cotton varieties with increased VW resistance is the most economical and effective method of controlling this disease and is greatly aided by understanding the genetics of resistance. This study aimed to investigate VW resistance in 240 F7 recombinant inbred lines (RIL) derived from a cross between MCU-5, which has good resistance, and Siokra 1-4, which is susceptible. Using a controlled environment bioassay, we found that resistance based on plant survival or shoot biomass was complex but with major contributions from chromosomes D03 and D09, with genomic prediction analysis estimating a prediction accuracy of 0.73 based on survival scores compared to 0.36 for shoot biomass. Transcriptome analysis of MCU-5 and Siokra 1-4 roots uninfected or infected with V. dahliae revealed that the two cultivars displayed very different root transcriptomes and responded differently to V. dahliae infection. Ninety-nine differentially expressed genes were located in the two mapped resistance regions and so are potential candidates for further identifying the genes responsible for VW resistance.

Genomic Selection as an Approach to Select for Reduced Aflatoxin Contamination in Peanut Under Terminal Drought Stress

Pre-harvest aflatoxin contamination (PAC) occurs when the peanut is exposed to severe drought and heat stress prior to harvest. Development of genotypes that are either resistant or limiting to Aspergillus infection and/or that can curtail aflatoxin production is a key objective in peanut breeding. Using SNP markers and phenotype data on aflatoxin resistance collected in previous years, we utilized genomic selection (GS) to study PAC resistance in peanut. The technique was validated in the Florida-07 x GP-NC WS 16 recombinant inbred population by assessing high heritability traits. GS was then deployed to study PAC resistance in the Tifrunner x C76-16 and Florida-07 x C76-16 populations. The resultant models yielded prediction accuracy values of 0.24 and 0.23 which while low, were comparable to the heritability values of 0.31 and 0.1 for each population, respectively. Using genomic estimated breeding values (GEBVs), entries were selected for two drought shelter studies. Manual scoring and multispectral imaging were used to acquire end season drought stress data. Low correlation values (-0.15 for shelter A and 0.32 for shelter B) were observed between the GEBVs and actual end season aflatoxin content. Correlations between visual drought ratings and PAC were also low (0.23 and 0.16 for shelter A and B respectively). While strong inverse correlations were observed between GNDVI and visual drought ratings (-0.74 and -0.73 for shelters A and B respectively), GNDVI did not confer a clear advantage for selection of PAC resistance. Ideally, the use of genome-spanning markers in GS may enable selection for a difficult to phenotype trait like PAC resistance. Although this study did not show clear advantages of the method over conventional selection, it is an important step for implementation of GS and the use of GEBVs for trait selection in peanut.

Development and validation of diagnostic markers for the reduced height gene Rht8 in wheat

AbstractWheat (Triticum aestivum L.) production is necessary for global food and nutrition security. Reducing plant height is an effective strategy to increase lodging resistance, harvest index, and eventually wheat yield. Rht8 is a gibberellic acid–sensitive reduced height (Rht) gene and has been cloned. Rht8 encodes a ribonuclease H‐like (RNHL) superfamily protein that reduces plant height without reduction in coleoptile length. High‐throughput diagnostic markers are not available for precise selection of RNHL in wheat breeding. In this study, we found that different cultivars may carry 1–3 copies of RNHLs on chromosome 2D, and only 2D carries the semi‐dwarf allele of RNHL although the wild‐type RNHL allele is detected in several other chromosomes. We developed two kompetitive allele specific PCR (KASP) markers, Rht8‐KASP‐V2 and Rht8‐KASP‐V3, based on the causal variation in RNHL. The two markers co‐segregated with plant height in a recombinant inbred population and were validated in a panel of hard winter wheat breeding lines from the 2022 Regional Germplasm Observation Nursery and Regional Performance Nursery. Rht8 has not been extensively deployed in US hard winter wheat and development of the diagnostic KASP markers will facilitate Rht8 transfer to US wheat cultivars.

Identification of QTLs for plant height and branching related traits in cultivated peanut

Plant height (PH), primary lateral branch length (PBL) and branch number (BN) are architectural components impacting peanut pod yield, biomass production and adaptivity to mechanical harvesting. In this study, a recombinant inbred population consisting of 181 individual lines was used to determine genetic controls of PH, PBL and BN across three environments. Phenotypic data collected from the population demonstrated continuous distributions and transgressive segregation patterns. Broad-sense heritability of PH, PBL and BN was found to be 0.87, 0.88 and 0.92, respectively. Unconditional individual environmental analysis revealed 35 additive QTLs with phenotypic variation explained (PVE) ranging from 4.57 to 21.68%. A two-round meta-analysis resulted in 24 consensus and 17 unique QTLs. Five unique QTLs exhibited pleiotropic effects and their genetic bases (pleiotropy or tight linkage) were evaluated. Joint analysis was performed to estimate the QTL by environment interaction (QEI) effects on PH, PBL and BN, which collectively explained phenotypic variations of 10.80, 11.02, and 7.89%, respectively. We identified 3 major and stable QTL regions (uq9-3, uq10-2 and uq16-1) on chromosomes 9, 10 and 16, spanning 1.43-1.53 Mb genomic regions. Candidate genes involved in phytohormones biosynthesis, signaling and cell wall development were proposed to regulate these morphological traits. These results provide valuable information for further genetic studies and development of molecular markers applicable for peanut architecture improvement.

Recombinant inbred lines derived from wide crosses in Pisum

Genomic resources are becoming available for Pisum but to link these to phenotypic diversity requires well marked populations segregating for relevant traits. Here we describe two such resources. Two recombinant inbred populations, derived from wide crosses in Pisum are described. One high resolution mapping population involves cv Caméor, for which the first pea whole genome assembly was obtained, crossed to JI0281, a basally divergent P. sativum sativum landrace from Ethiopia. The other is an inter sub-specific cross between P. s. sativum and the independently domesticated P. s. abyssinicum. The corresponding genetic maps provide information on chromosome level sequence assemblies and identify structural differences between the genomes of these two Pisum subspecies. In order to visualise chromosomal translocations that distinguish the mapping parents, we created a simplified version of Threadmapper to optimise it for interactive 3-dimensional display of multiple linkage groups. The genetic mapping of traits affecting seed coat roughness and colour, plant height, axil ring pigmentation, leaflet number and leaflet indentation enabled the definition of their corresponding genomic regions. The consequence of structural rearrangement for trait analysis is illustrated by leaf serration. These analyses pave the way for identification of the underlying genes and illustrate the utility of these publicly available resources. Segregating inbred populations derived from wide crosses in Pisum, together with the associated marker data, are made publicly available for trait dissection. Genetic analysis of these populations is informative about chromosome scale assemblies, structural diversity in the pea genome and has been useful for the fine mapping of several discrete and quantitative traits.

Registration of Golden Promise/Otis barley recombinant inbred line mapping population

AbstractA recombinant inbred line mapping population was developed from a cross between the heritage malting barley (Hordeum vulgare ssp. vulgare) cultivar ‘Golden Promise’ and ‘Otis’, a feed barley cultivar developed in the 1960s suitable for the high dry plains. The Golden Promise/Otis recombinant inbred line (RIL) population (MP‐3, NSL 545640 MAP) consists of 190 F5:7 individuals. The parental lines exhibited significant differences in several agronomic traits including height, heading date, yield/plant, and lodging. Transgressive segregation in the RILs was evidenced by the broad range of values observed for these agronomic traits. The RIL population was genotyped using the Illumina 50k iSelect single nucleotide polymorphism (SNP) arrays. Of the 10,810 polymorphic markers that were identified between the two parents, 4617 markers were used for generating a genetic map that spanned 4566 cM with an average distance of 1 cM between markers. The fact that Golden Promise is a malting cultivar developed in the United Kingdom, versus Otis, a feed barley bred in the United States for dryland cultivation, indicates that this population may be useful in identifying the genetic basis of many other traits.

Influence of organic plant breeding on the rhizosphere microbiome of common bean (Phaseolus vulgaris L.).

We now recognize that plant genotype affects the assembly of its microbiome, which in turn, affects essential plant functions. The production system for crop plants also influences the microbiome composition, and as a result, we would expect to find differences between conventional and organic production systems. Plant genotypes selected in an organic regime may host different microbiome assemblages than those selected in conventional environments. We aimed to address these questions using recombinant inbred populations of snap bean that differed in breeding history. Rhizosphere microbiomes of conventional and organic common beans (Phaseolus vulgaris L.) were characterized within a long-term organic research site. The fungal and bacterial communities were distinguished using pooled replications of 16S and ITS amplicon sequences, which originated from rhizosphere samples collected between flowering and pod set. Bacterial communities significantly varied between organic and conventional breeding histories, while fungal communities varied between breeding histories and parentage. Within the organically-bred populations, a higher abundance of a plant-growth-promoting bacteria, Arthrobacter pokkalii, was identified. Conventionally-bred beans hosted a higher abundance of nitrogen-fixing bacteria that normally do not form functional nodules with common beans. Fungal communities in the organically derived beans included more arbuscular mycorrhizae, as well as several plant pathogens. The results confirm that the breeding environment of crops can significantly alter the microbiome community composition of progeny. Characterizing changes in microbiome communities and the plant genes instrumental to these changes will provide essential information about how future breeding efforts may pursue microbiome manipulation.

Genome-Wide Analysis of Amino Acid Transporter Gene Family Revealed That the Allele Unique to the Aus Variety Is Associated with Amino Acid Permease 17 (OsAAP17) Amplifies Both the Tiller Count and Yield in Indica Rice (Oryza sativa L.)

Amino acid transporters (AATs) play a crucial role in facilitating the movement of amino acids across cellular membranes, which is vital for the growth and development of plants. Amino acid permease (AAP), which belongs to the AAT family, has been the subject of extensive functional research in plants. Although its importance is recognized, a comprehensive grasp of this family’s dynamics in indica rice remains lacking. In this investigation, a total of 27 AAP genes were identified in the genome of indica rice. Further, the phylogenetic analysis unveiled that the 69 AAP genes from both the model species and other plant species could be classified into 16 distinct subfamilies. The analysis of chromosomal mapping revealed an uneven distribution of the 27 OsAAP genes across the 12 rice chromosomes. Notably, the OsAAP family displayed a total of 10 duplicated gene pairs, along with the identification of numerous conserved motifs. The examination of cis-elements within OsAAP genes unveiled that their promoters contain cis-elements related to phytohormones, plant growth and development, as well as stress responses. Additionally, transcriptome profiling demonstrated that a substantial portion of these genes exhibited responsiveness to various hormones, with their activation spanning multiple tissues and developmental stages in rice. The study identified miRNAs with a specific affinity for OsAAP genes. Out of the 27 OsAAP genes investigated, seventeen were discovered to be targeted by a total of forty-three miRNAs. Furthermore, the aus allele of OsAAP3 that we named OsAAP17 was validated for its effect on productive tillers and yield, and seventeen genetic variants of OsAAP17 were found to be associated with a culm number in indica rice. In addition, indica rice varieties were monomorphic, while aus genotypes displayed polymorphism for OsAAP17 gene-specific in/dels. Moreover, in Season II (rabi season), it was found that the aus allele of OsAAP17 increased the number of productive tillers and the single plant yield by 22.55% and 9.67%, respectively, in a recombinant inbred population created by crossing N22 and JR 201. Remarkably, this enhancement was more pronounced during the dry cultivation season, highlighting the influence of environmental factors in the regulation of tiller numbers mediated by OsAAP17. The discoveries presented here lay a strong foundation for further exploration into the roles of OsAAP family genes across a range of developmental processes. Therefore, the identified allelic variations in the utilization of OsAAP17 has the potential to enhance rice crop production via molecular breeding in the changing climate scenario.

Phenotypic Variation of Component Traits Affecting Maturity in Cultivated Peanut (Arachis hypogaea L.)

A wide range of time-to-maturity exists among peanut accessions and cultivars, and it is a complex trait likely controlled by many genes and influenced by the environment. Underground formation of fruit coupled with indeterminate growth habit makes peanut a difficult crop species to explore genetic controls of this trait. Dividing the total phenotype of time-to-maturity into component traits can facilitate the dissection of genetic pathways controlling maturity in peanut. In this study, component traits contributing to time-to-maturity included flowering on the main stem, flowering rate, flower-to-peg conversion ratio, internode length, distribution of reproductive and vegetative nodes, branch numbers, percentage of harvestable pods, and harvest index, which were quantified for six genetically diverse peanut genotypes. Statistically significant differences were detected for all measured traits among the tested genotypes. These genotypes are parental lines of four established recombinant inbred populations. Populations with contrasting parental phenotypic values could be utilized for further QTL mapping of the relevant traits.

Use of genomic prediction to screen sorghum B-lines in hybrid testcrosses.

Use of trifluoromethanesulfonamide (TFMSA), a male gametocide, increases the opportunities to identify promising B-lines because large quantities of F1 seed can be generated prior to the laborious task of B-line sterilization. Combining TFMSA technology with genomic selection could efficiently evaluate sorghum B-lines in hybrid combination to maximize the rates of genetic gain of the crop. This study used two recombinant inbred B-line populations, consisting of 217 lines, which were testcrossed to two R-lines to produce 434 hybrids. Each population of testcross hybrids were evaluated across five environments. Population-based genomic prediction models were assessed across environments using three different cross-validation (CV) schemes, each with 70% training and 30% validation sets. The validation schemes were as follows: CV1-hybrids chosen randomly for validation; CV2-B-lines were randomly chosen, and each chosen B-line had one of the two corresponding testcross hybrids randomly chosen for the validation; and CV3-B-lines were randomly chosen, and each chosen B-line had both corresponding testcross hybrids chosen for the validation. CV1 and CV2 presented the highest prediction accuracies; nonetheless, the prediction accuracies of the CV schemes were not statistically different in many environments. We determined that combining the B-line populations could improve prediction accuracies, and the genomic prediction models were able to effectively rank the poorest 70% of hybrids even when genomic prediction accuracies themselves were low. Results indicate that combining genomic prediction models and TFMSA technology can effectively aid breeders in predicting B-line hybrid performance in early generations prior to the laborious task of generating A/B-line pairs.

Genetic analysis and physical mapping of oat adult plant resistance loci against Puccinia coronata f. sp. avenae.

Six quantitative trait loci (QTL) for adult plant resistance (APR) against oat crown rust (Puccinia coronata f. sp. avenae) were identified from mapping three recombinant inbred populations (RILs). Using genotyping-by-sequencing with markers called against the OT3098 v1 reference genome, the QTL were mapped on six different chromosomes, namely: Chr1D, Chr4D, Chr5A, Chr5D, Chr7A, and Chr7C. Composite interval mapping with marker cofactor selection showed that the phenotypic variance explained by all identified QTL for coefficient of infection range from 12.2 to 46.9%, while heritability estimates ranged from 0.11 to 0.38. The significant regions were narrowed down to intervals of 3.9 to 25 cM, equivalent to physical distances of 11 to 133 Mb. At least two flanking SNP markers were identified within 10 cM of each QTL that could be used in marker-assisted introgression, pyramiding, and selection. The additive effects of the QTL in each population were determined using SNP haplotype data, which showed significantly lower coefficient of infection (CI) in lines homozygous for the resistant alleles. Analysis of pairwise linkage disequilibrium also revealed high correlation of markers and presence of linkage blocks in the significant regions. To further facilitate marker-assisted breeding, Polymerase Chain Reaction Allelic Competitive Extension (PACE) markers for the APR loci were developed. Putative candidate genes were also identified in each of the significant regions, which include resistance gene analogs that encode for kinases, ligases, and predicted receptors of avirulence proteins from pathogens.

Molecular mapping of QTL for type I Fusarium head blight resistance in two recombinant inbred lines wheat populations

AbstractFusarium head blight (FHB) is a major concern for wheat production and food safety, globally. Resistance to infection (type I resistance) is important for breeding varieties with good FHB resistance. To better understand the genetic architecture underlying type I FHB resistance, quantitative trait loci (QTL) mapping was conducted using two recombinant inbred line populations derived from the crosses Yangmai 4 (YM4)/Yanzhan 1 (YZ1) and Yangmai 5 (YM5)/YZ1. A total of five resistance QTL, including QFhb.yaas‐2D, QFhb.yaas‐4D, QFhb.yaas‐5B, QFhb.yaas‐6B, and QFhb.yaas‐3A, were detected from these two populations. Except for QFhb.yaas‐2D and QFhb.yaas‐5B, the resistance effects of all the other QTLs are derived from YM4 or YM5. QFhb.yaas‐4D is a common QTL detected both in YM4/YZ1 and YM5/YZ1 populations. QFhb.yaas‐2D, QFhb.yaas‐4D, and QFhb.yaas‐5B were colocalized with known plant height (PH) genes Rht8, Rht‐D1, and flowering date (FD) gene Vrn‐B1. However, QFhb.yaas‐6B and QFhb.yaas‐3A were not associated with PH and FD. Kompetitive Allele‐Specific PCR markers for QFhb.yaas‐6B and QFhb.yaas‐3A had been developed and validated in an additional panel of 211 wheat cultivars/lines. The result showed that these two resistance alleles decreased 46.65% of the percentage of diseased spikelets. These results provide valuable information for the fine mapping of QFhb.yaas‐6B and QFhb.yaas‐3A in the future.

Fine mapping and genetic analysis identified a C2H2-type zinc finger as a candidate gene for heading date regulation in wheat.

A minor-effect QTL, Qhd.2AS, that affects heading date in wheat was mapped to a genomic interval of 1.70-Mb on 2AS, and gene analysis indicated that the C2H2-type zinc finger protein gene TraesCS2A02G181200 is the best candidate for Qhd.2AS. Heading date (HD) is a complex quantitative trait that determines the regional adaptability of cereal crops, and identifying the underlying genetic elements with minor effects on HD is important for improving wheat production in diverse environments. In this study, a minor QTL for HD that we named Qhd.2AS was detected on the short arm of chromosome 2A by Bulked Segregant Analysis and validated in a recombinant inbred population. Using a segregating population of 4894 individuals, Qhd.2AS was further delimited to an interval of 0.41cM, corresponding to a genomic region spanning 1.70Mb (from 138.87 to 140.57Mb) that contains 16 high-confidence genes based on IWGSC RefSeq v1.0. Analyses of sequence variations and gene transcription indicated that TraesCS2A02G181200, which encodes a C2H2-type zinc finger protein, is the best candidate gene for Qhd.2AS that influences HD. Screening a TILLING mutant library identified two mutants with premature stop codons in TraesCS2A02G181200, both of which exhibited a delay in HD of 2-4days. Additionally, variations in its putative regulatory sites were widely present in natural accession, and we also identified the allele which was positively selected during wheat breeding. Epistatic analyses indicated that Qhd.2AS-mediated HD variation is independent of VRN-B1 and environmental factors. Phenotypic investigation of homozygous recombinant inbred lines (RILs) and F2:3 families showed that Qhd.2AS has no negative effect on yield-related traits. These results provide important cues for refining HD and therefore improving yield in wheat breeding programs and will deepen our understanding of the genetic regulation of HD in cereal plants.

Genomic architecture of leaf senescence in sorghum (Sorghum bicolor).

Leaf senescence in sorghum is primarily controlled by the progression, but not by the onset of senescence. The senescence-delaying haplotypes of 45 key genes accentuated from landraces to improved lines. Leaf senescence is a genetically programmed developmental process and plays a central role for plant survival and crop production by remobilising nutrients accumulated in senescent leaves. In theory, the ultimate outcome of leaf senescence is determined by the onset and progression of senescence, but how these two processes contribute to senescence is not fully illustrated in crops and the genetic basis for them is not well understood. Sorghum (Sorghum bicolor), which is known for the remarkable stay-green trait, is ideal for dissecting the genomic architecture underlying the regulation of senescence. In this study, a diverse panel of 333 sorghum lines was explored for the onset and progression of leaf senescence. Trait correlation analysis showed that the progression of leaf senescence, rather than the onset of leaf senescence, significantly correlated with variations of the final leaf greenness. This notion was further supported by GWAS, which identified 31 senescence-associated genomic regions containing 148 genes, of which 124 were related to the progression of leaf senescence. The senescence-delaying haplotypes of 45 key candidate genes were enriched in lines with extremely prolonged senescence duration, while senescence-promoting haplotypes in those with extremely accelerated senescence. Haplotype combinations of these genes could well explain the segregation of the senescence trait in a recombinant inbred population. We also demonstrated that senescence-delaying haplotypes of candidate genes were under strong selection during sorghum domestication and genetic improvement. Together, this research advanced our understanding of crop leaf senescence and provided a suite of candidate genes for functional genomics and molecular breeding.

Inoculum production of Phytophthora medicaginis can be used to screen for partial resistance in chickpea genotypes.

Phytophthora root rot caused by Phytophthora medicaginis is an important disease of chickpeas (Cicer arietinum) in Australia with limited management options, increasing reliance on breeding for improved levels of genetic resistance. Resistance based on chickpea-Cicer echinospermum crosses is partial with a quantitative genetic basis provided by C. echinospermum and some disease tolerance traits originating from C. arietinum germplasm. Partial resistance is hypothesised to reduce pathogen proliferation, while tolerant germplasm may contribute some fitness traits, such as an ability to maintain yield despite pathogen proliferation. To test these hypotheses, we used P. medicaginis DNA concentrations in the soil as a parameter for pathogen proliferation and disease assessments on lines of two recombinant inbred populations of chickpea-C. echinospermum crosses to compare the reactions of selected recombinant inbred lines and parents. Our results showed reduced inoculum production in a C. echinospermum backcross parent relative to the C. arietinum variety Yorker. Recombinant inbred lines with consistently low levels of foliage symptoms had significantly lower levels of soil inoculum compared to lines with high levels of visible foliage symptoms. In a separate experiment, a set of superior recombinant inbred lines with consistently low levels of foliage symptoms was tested for soil inoculum reactions relative to control normalised yield loss. The in-crop P. medicaginis soil inoculum concentrations across genotypes were significantly and positively related to yield loss, indicating a partial resistance-tolerance spectrum. Disease incidence and the rankings for in-crop soil inoculum were correlated strongly to yield loss. These results indicate that soil inoculum reactions may be useful to identify genotypes with high levels of partial resistance.

Genetic Dissection and Germplasm Selection of the Low Crude Fiber Component in Brassica napus L. Shoots.

Brassica napus is one of the most important oil crops in the world, and B. napus shoots are nutrient-rich fresh vegetables. The crude fiber (CF) component is one of the most important factors affecting the taste quality of B. napus shoots, but the factors underlying the desirable low-CF trait remain poorly understood. In this study, a high-density single-nucleotide polymorphism (SNP) map was used to map quantitative trait loci (QTLs) for five CF-related traits in a recombinant inbred population. A total of 49 QTLs were obtained in four environments, including eleven, twelve, eight, twelve and six QTLs for content of neutral detergent fiber, acid detergent fiber, acid detergent lignin, hemicellulose and cellulose, respectively. The phenotypic variation explained by single QTL ranged from 4.62% to 14.76%. Eight of these QTLs were further integrated into four unique QTLs, which controlled two different traits simultaneously. Five CF-component-related candidate genes were identified, among which BnaC03g07110D and BnaC07g21271D were considered to be the most likely candidate genes. In addition, five lines with low CF content were selected, which can be used as excellent germplasm resources in breeding. The QTLs identified in this study will contribute to our understanding of the genetic mechanism of CF and can be used as targets for reducing CF content in B. napus shoots. In addition, this study also provided excellent germplasm resources for low CF content breeding.

Positional cloning and characterization reveal the role of a miRNA precursor gene ZmLRT in the regulation of lateral root number and drought tolerance in maize.

Lateral roots play essential roles in drought tolerance in maize (Zea mays L.). However, the genetic basis for the variation in the number of lateral roots in maize remains elusive. Here, we identified a major quantitative trait locus (QTL), qLRT5-1, controlling lateral root number using a recombinant inbred population from a cross between the maize lines Zong3 (with many lateral roots) and 87-1 (with few lateral roots). Fine-mapping and functional analysis determined that the candidate gene for qLRT5-1, ZmLRT, expresses the primary transcript for the microRNA miR166a. ZmLRT was highly expressed in root tips and lateral root primordia, and knockout and overexpression of ZmLRT increased and decreased lateral root number, respectively. Compared with 87-1, the ZmLRT gene model of Zong3 lacked the second and third exons and contained a 14 bp deletion at the junction between the first exon and intron, which altered the splicing site. In addition, ZmLRT expression was significantly lower in Zong3 than in 87-1, which might be attributed to the insertions of a transposon and over large DNA fragments in the Zong3 ZmLRT promoter region. These mutations decreased the abundance of mature miR166a in Zong3, resulting in increased lateral roots at the seedling stage. Furthermore, miR166a post-transcriptionally repressed five development-related class-III homeodomain-leucine zipper genes. Moreover, knockout of ZmLRT enhanced drought tolerance of maize seedlings. Our study furthers our understanding of the genetic basis of lateral root number variation in maize and highlights ZmLRT as a target for improving drought tolerance in maize.

Genetic mapping of a pollinator preference trait: Nectar volume in sunflower (Helianthus annuus L.).

Although high pollinator visitation is crucial to ensure the yields of pollinator-dependent crops, the quantitative trait loci (QTL) controlling nectar volume in sunflower (Helianthus annuus L.), a pollinator preference trait, have yet to be identified. To address this, a recombinant inbred line mapping population, derived from lines with contrasting nectar volume, was used to identify loci responsible for the phenotype. As a result, linkage mapping and QTL analysis discovered major loci on chromosomes 2 and 16 that are associated with variation in nectar volume in sunflower. Increased nectar volume is also associated with increased sugars and total energy available per floret. The regions on chromosomes 2 and 16 associated with the nectar phenotype exhibit indications of chromosome structural variation, such that the phenotype is associated with rearrangements affecting regions containing hundreds of genes. Candidate genes underlying QTL on chromosomes 9 and 16 are homologous to genes with nectary function in Arabidopsis. These results have implications for sunflower breeding, to enhance pollination efficiency in sunflower, as well as current and future studies on sunflower evolution.