The Hessian fly resistance gene HvRHF1 is localized in an NBS-LRR gene cluster in barley.

Hessian fly (Mayetiola destructor Say) is a significant pest in cereal crops, causing substantial yield losses worldwide. While host resistance is the most efficient method for pest control, research on genetic characterization of Hessian fly resistance in barley (Hordeum vulgare L.) has been limited, and the underlying resistance mechanism remains largely unknown. In this study, we conducted fine mapping of a crucial Hessian fly resistance locus, known as HvRHF1, using a biparental population. Assisted with genetic markers and robust phenotyping assay, we pinpointed the HvRHF1 gene to an ~ 82 kb region on chromosome 4H. Gene prediction and annotation revealed that the HvRHF1 locus comprises three complete NBS-LRR genes, which are characteristic of disease resistance genes. As a result, our study not only provides valuable resources for resistance in barley and genetic tools for breeding, but also identifies candidate genes that lay the foundation for cloning HvRHF1. This endeavor will significantly contribute to our understanding of the molecular mechanisms underlying cereal resistance to Hessian fly.

Genome-Wide Association Study of Host Resistance to Hessian Fly in Barley.

The Hessian fly (HF), Mayetiola destructor (Diptera: Cecidomyiidae), is one of the most devastating insect pests of cereals including wheat, barley, and rye. Although wheat is the preferred host for HF, this continuously evolving pest has been emerging as a threat to barley production. However, characterization and identification of genetic resistance to HF has not been conducted in barley. In the present study, we used a genome-wide association study (GWAS) to identify barley resistance loci to HF using a geographically diverse set of 234 barley accessions. The results showed that around 90% of barley lines were highly susceptible, indicating a significant vulnerability to HF in barley, and a total of 29 accessions were resistant, serving as potential resistance resources. GWAS with a mixed linear model revealed two marker-trait associations, both on chromosome 4H. The resistance loci and associated markers will facilitate barley improvement and development for breeders. In addition, our results are fundamental for genetic studies to understand the HF resistance mechanism in barley.

Chromosome diversity in Dasypyrum villosum, an important genetic and trait resource for hexaploid wheat engineering.

BACKGROUND AND AIMS: Dasypyrum villosum (2n = 2x = 14) harbours potentially beneficial genes for hexaploid and tetraploid wheat improvement. Highly diversified chromosome variation exists among and within accessions due to its open-pollination nature. The wheat-D. villosum T6VS·6AL translocation was widely used in breeding mainly because gene Pm21 in the 6VS segment conferred high and lasting powdery mildew resistance. However, the widespread use of this translocation may narrow the genetic base of wheat. A better solution is to utilize diversified D. villosum accessions as the genetic source for wheat breeding. Analysis of cytological and genetic polymorphisms among D. villosum accessions also provides genetic evolution information on the species. Using cytogenetic and molecular tools we analysed genetic polymorphisms among D. villosum accessions and developed consensus karyotypes to assist the introgression of beneficial genes from D. villosum into wheat. METHODS: A multiplex probe of repeats for FISH, GISH and molecular markers were used to detect chromosome polymorphisms among D. villosum accessions. Polymorphic signal block types, chromosome heterogeneity and heterozygosity, and chromosome polymorphic information content were used in genetic diversity analysis. KEY RESULTS: Consensus karyotypes of D. villosum were developed, and the homoeologous statuses of individual D. villosum chromosomes relative to wheat were determined. Tandem repeat probes of pSc119.2, (GAA)10 and the AFA family produced high-resolution signals and not only showed different signal patterns in D. villosum chromosomes but also revealed the varied distribution of tandem repeats among chromosomes and accessions. A total of 106 polymorphic chromosomes were identified from 13 D. villosum accessions and high levels of chromosomal heterozygosity and heterogeneity were observed. A subset of 56 polymorphic chromosomes was transferred into durum wheat through wide crosses, and seven polymorphic chromosomes are described in two newly developed durum-D. villosum amphidiploids. CONCLUSIONS: Consensus karyotypes of D. villosum and oligonucleotide FISH facilitated identification of polymorphic signal blocks and a high level of chromosomal heterozygosity and heterogeneity among D. villosum accessions, seen in newly developed amphiploids. The abundant genetic diversity of D. villosum and range of alleles, exploitable through interploid crosses, backcrosses and recombination (chromosome engineering), allow introduction of biotic and abiotic stress resistances into wheat, translating into increasing yield, end-use quality and crop sustainability.

Function and evolution of allelic variations of Sr13 conferring resistance to stem rust in tetraploid wheat (Triticum turgidum L.).

The resistance gene Sr13 is one of the most important genes in durum wheat for controlling stem rust caused by Puccinia graminis f. sp. tritici (Pgt). The Sr13 functional gene CNL13 has haplotypes R1, R2 and R3. The R1/R3 and R2 haplotypes were originally designated as alleles Sr13a and Sr13b, respectively. To detect additional Sr13 alleles, we developed Kompetitive allele specific PCR (KASP™) marker KASPSr13 and four semi-thermal asymmetric reverse PCR markers, rwgsnp37-rwgsnp40, based on the CNL13 sequence. These markers were shown to detect R1, R2 and R3 haplotypes in a panel of diverse tetraploid wheat accessions. We also observed the presence of Sr13 in durum line CAT-A1, although it lacked any of the known haplotypes. Sequence analysis revealed that CNL13 of CAT-A1 differed from the susceptible haplotype S1 by a single nucleotide (C2200T) in the leucine-rich repeat region and differed from the other three R haplotypes by one or two additional nucleotides, confirming that CAT-A1 carries a new (R4) haplotype. Stem rust tests on the monogenic, transgenic and mutant lines showed that R1 differed from R3 in its susceptibility to races TCMJC and THTSC, whereas R4 differed from all other haplotypes for susceptibility to TTKSK, TPPKC and TCCJC. Based on these differences, we designate the R1, R3 and R4 haplotypes as alleles Sr13a, Sr13c and Sr13d, respectively. This study indicates that Sr13d may be the primitive functional allele originating from the S1 haplotype via a point mutation, with the other three R alleles probably being derived from Sr13d through one or two additional point mutations.

Frequent numerical and structural chromosome changes in early generations of synthetic hexaploid wheat.

Modern hexaploid wheat (Triticum aestivum L.; AABBDD) has evolved from a hybrid of tetraploid wheat (closely related to Triticum turgidum L. ssp. durum (Desf.) Husn., AABB) and goatgrass (Aegilops tauschii Coss., DD). Variations in chromosome structure and ploidy have played important roles in wheat evolution. How these variations occur and their role in expanding the genetic diversity of modern wheat remain largely unknown. Synthetic hexaploid wheat (SHW) can be used to investigate chromosome variations that occur during the early generations of existence. SHW lines derived by crossing durum wheat 'Langdon' with 12 Ae. tauschii accessions were analyzed using oligonucleotide probe multiplex fluorescence in situ hybridization (FISH) of metaphase chromosomes and SNP markers. Cluster analysis based on SNP markers categorizes them into three groups. Among 702 plants from the S8 and S9 generations, 415 (59.12%) carried chromosome variations involving all 21 chromosomes, but with different frequencies for each chromosome and sub-genome. Total chromosome variation frequencies varied between lines, but there was no significant difference among the three groups. The non-random chromosome variations in the SHW lines detected in this study may indicate that similar variations occurred in the early stages of wheat polyploidization and played important roles in wheat evolution.

A new strategy for using historical imbalanced yield data to conduct genome-wide association studies and develop genomic prediction models for wheat breeding.

Using imbalanced historical yield data to predict performance and select new lines is an arduous breeding task. Genome-wide association studies (GWAS) and high throughput genotyping based on sequencing techniques can increase prediction accuracy. An association mapping panel of 227 Texas elite (TXE) wheat breeding lines was used for GWAS and a training population to develop prediction models for grain yield selection. An imbalanced set of yield data collected from 102 environments (year-by-location) over 10 years, through testing yield in 40-66 lines each year at 6-14 locations with 38-41 lines repeated in the test in any two consecutive years, was used. Based on correlations among data from different environments within two adjacent years and heritability estimated in each environment, yield data from 87 environments were selected and assigned to two correlation-based groups. The yield best linear unbiased estimation (BLUE) from each group, along with reaction to greenbug and Hessian fly in each line, was used for GWAS to reveal genomic regions associated with yield and insect resistance. A total of 74 genomic regions were associated with grain yield and two of them were commonly detected in both correlation-based groups. Greenbug resistance in TXE lines was mainly controlled by Gb3 on chromosome 7DL in addition to two novel regions on 3DL and 6DS, and Hessian fly resistance was conferred by the region on 1AS. Genomic prediction models developed in two correlation-based groups were validated using a set of 105 new advanced breeding lines and the model from correlation-based group G2 was more reliable for prediction. This research not only identified genomic regions associated with yield and insect resistance but also established the method of using historical imbalanced breeding data to develop a genomic prediction model for crop improvement. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-022-01287-8.

Predominant wheat-alien chromosome translocations in newly developed wheat of China.

Founder wheat lines have played key role in Chinese wheat improvement. Wheat-Dasypyrum villosum translocation T6VS·6AL has been widely used in wheat breeding in recent years due to its high level of powdery mildew resistance and other beneficial genes. Reference oligo-nucleotide multiplex probe (ONMP)-FISH karyotypes of six T6VS·6AL donor lines were developed and used for characterizing 32 derivative cultivars and lines. T6VS·6AL was present in 27 cultivar/lines with 20 from southern China. Next, ONMP-FISH was used to study chromosome constitution of randomly collected wheat cultivars and advanced breeding lines from southern and northern regions of China: 123 lines from the regional test plots of southern China and 110 from northern China. In southern China, T6VS·6AL (35.8%) was the most predominant variation, while T1RS·1BL (27.3%) was the most predominant in northern China. The pericentric inversion perInv 6B derived from its founder wheat Funo and Abbondaza was the second most predominant chromosome variant in both regions. Other chromosome variants were present in very low frequencies. Additionally, 167 polymorphic chromosome types were identified. Based on these variations, 271 cultivars and lines were clustered into three groups, including southern, northern, and mixed groups that contained wheat from both regions. Different dominant chromosome variations were seen, indicating chromosome differentiation in the three groups of wheat. The clearly identified wheat lines with T6VS·6AL in different backgrounds and oligonucleotide probe set will facilitate their utilization in wheat breeding and in identifying other beneficial traits that may be linked to this translocation. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-021-01206-3.

Physical organization of repetitive sequences and chromosome diversity of barley revealed by fluorescence in situ hybridization (FISH).

Fluorescence in situ hybridization (FISH) using oligonucleotides is a simple and convenient method for chromosome research. In this study, 34 of 46 previously developed oligonucleotides produced signals in barley. Together with two plasmid clones and one PCR-amplified cereal centromere repeat (CCS1) probe, 37 repetitive sequences were chromosomally located produced three types of signals covering different positions on the chromosomes. The centromeric and pericentric regions had a more complex genomic organization and sequence composition probably indicative of higher contents of heterochromatin. An efficient multi-plex probe containing eight oligonucleotides and a plasmid clone of 45S rDNA was developed. Thirty-three barley karyotypes were developed and compared. Among them, 11 irradiation-induced mutants of cultivar 08-49 showed no chromosomal variation, whereas 22 cultivar and landrace accessions contained 28 chromosomal polymorphisms. Chromosome 4H was the most variable and 6H was the least variable based on chromosome polymorphic information content (CPIC). Five polymorphic chromosomes (1H-2, 2H-1, 3H-3, 5H-2, and 6H-2) were dominant types, each occurring in more than 50% of accessions. The multi-plex probe should facilitate identification of further chromosomal polymorphisms in barley.

Structural chromosome rearrangements and polymorphisms identified in Chinese wheat cultivars by high-resolution multiplex oligonucleotide FISH.

KEY MESSAGE: High-resolution multiplex oligonucleotide FISH revealed the frequent occurrence of structural chromosomal rearrangements and polymorphisms in widely grown wheat cultivars and their founders. Over 2000 wheat cultivars including 19 founders were released and grown in China from 1949 to 2000. To understand the impact of breeding selection on chromosome structural variations, high-resolution karyotypes of Chinese Spring (CS) and 373 Chinese cultivars were developed and compared by FISH (fluorescence in situ hybridization) using an oligonucleotide multiplex probe based on repeat sequences. Among them, 148 (39.7%) accessions carried 14 structural rearrangements including three single translocations (designated as T), eight reciprocal translocations (RT), one pericentric inversion (perInv), and two combined variations having both the deletion and single translocations. Five rearrangements were traced to eight founders, including perInv 6B detected in 57 cultivars originating from Funo, Abbondanza, and Fan 6, T 1RS∙1BL in 47 cultivars derived from the Lovrin series, RT 4AS∙4AL-1DS/1DL∙1DS-4AL in 31 varieties from Mazhamai and Bima 4, RT 1RS∙7DL/7DS∙1BL in three cultivars was from Aimengniu, and RT 5BS∙5BL-5DL/5DS∙5DL-5BL was only detected in Youzimai. In addition to structural rearrangements, 167 polymorphic chromosome blocks (defined as unique signal patterns of oligonucleotide repeat probes distributed within chromosomes) were identified, and 59 were present in one or more founders. Some specific types were present at high frequencies indicating selective blocks in Chinese wheat varieties. All cultivars and CS were clustered into four groups and 15 subgroups at chromosome level. Common block patterns occurred in the same subgroup. Origin, geographic distribution, probable adaptation to specific environments, and potential use of these chromosomal rearrangements and blocks are discussed.

A simple and efficient non-denaturing FISH method for maize chromosome differentiation using single-strand oligonucleotide probes.

Single-strand oligonucleotides (SSONs hereafter) as probes are becoming a powerful method of chromosome painting in many species. In this study, nine SSONs ((ACT)10, (ACT)19, Knob-1, Knob-2, Knob-3, CentC69-1, MR68-3, K10-72-1, and TR1-357-2) were developed and used for chromosome identification in 16 maize (Zea mays L., 2n = 20) inbred lines and hybrids by non-denaturing fluorescence in situ hybridization (ND-FISH). Each SSON produced clear signals on 2-10 chromosomes of inbred lines B73 and Mo17. A multiplex probe set containing four SSONs ((ACT)10, Knob-2, CentC69-1, and MR68-3) clearly characterized all maize chromosomes in the 16 lines by a single round of ND-FISH and revealed genetic variation at a chromosome level. For example, unique signals on chromosome 6 clearly distinguished all 16 genotypes. The SSONs and multiplex probe developed in this research will facilitate genotype identification and chromosome research in maize.

Development of oligonucleotides and multiplex probes for quick and accurate identification of wheat and Thinopyrum bessarabicum chromosomes.

In comparison with general FISH for preparing probes in terms of time and cost, synthesized oligonucleotide (oligo hereafter) probes for FISH have many advantages such as ease of design, synthesis, and labeling. Low cost and high sensitivity and resolution of oligo probes greatly simplify the FISH procedure as a simple, fast, and efficient method of chromosome identification. In this study, we developed new oligo and oligo multiplex probes to accurately and efficiently distinguish wheat (Triticum aestivum, 2n = 6x, AABBDD) and Thinopyrum bessarabicum (2n = 2x = 14, JJ) chromosomes. The oligo probes contained more nucleotides or more repeat units that produced stronger signals for more efficient chromosome painting. Four Th. bessarabicum-specific oligo probes were developed based on genomic DNA sequences of Th. bessarabicum chromosome arm 4JL, and one of them (oligo DP4J27982) was pooled with the oligo multiplex #1 to simultaneously detect wheat and Th. bessarabicum chromosomes for quick and accurate identification of Chinese Spring (CS) - Th. bessarabicum alien chromosome introgression lines. Oligo multiplex #4 revealed chromosome variations among CS and eight wheat cultivars by a single round of FISH analysis. This research demonstrated the high efficiency of using oligos and oligo multiplexes in chromosome identification and manipulation.

Chromosome aberrations induced by zebularine in triticale.

Chromosome engineering is an important approach for generating wheat germplasm. Efficient development of chromosome aberrations will facilitate the introgression and application of alien genes in wheat. In this study, zebularine, a DNA methylation transferase inhibitor, was successfully used to induce chromosome aberrations in the octoploid triticale cultivar Jinghui#1. Dry seeds were soaked in zebularine solutions (250, 500, and 750 µmol/L) for 24 h, and the 500 µmol/L treatment was tested in three additional treatment times, i.e., 12, 36, and 48 h. All treatments induced aberrations involving wheat and rye chromosomes. Of the 920 cells observed in 67 M1 plants, 340 (37.0%) carried 817 aberrations with an average of 0.89 aberrations per cell (range: 0-12). The aberrations included probable deletions, telosomes and acentric fragments (49.0%), large segmental translocations (28.9%), small segmental translocations (17.1%), intercalary translocations (2.6%), long chromosomes that could carry more than one centromere (2.0%), and ring chromosomes (0.5%). Of 510 M2 plants analyzed, 110 (21.6%) were found to carry stable aberrations. Such aberrations included 79 with varied rye chromosome numbers, 7 with wheat and rye chromosome translocations, 15 with possible rye telosomes/deletions, and 9 with complex aberrations involving variation in rye chromosome number and wheat-rye translocations. These indicated that aberrations induced by zebularine can be steadily transmitted, suggesting that zebularine is a new efficient agent for chromosome manipulation.

Physical mapping of chromosome 4J of Thinopyrum bessarabicum using gamma radiation-induced aberrations.

KEY MESSAGE: Gamma radiation induced a series of structural aberrations involving Thinopyrum bessarabicum chromosome 4J. The aberrations allowed for deletion mapping of 101 4J-specific markers and fine mapping of blue-grained gene BaThb. Irradiation can induce translocations and deletions to assist physically locating genes and markers on chromosomes. In this study, a 12-Gy dosage of (60)Co-γ was applied to pollen and eggs of a wheat (Triticum aestivum) landrace Chinese Spring (CS)-Thinopyrum bessarabicum chromosome 4J disomic addition line (DA4J), and the gametes from irradiated plants were fertilized with normal CS eggs or pollen to produce M1 seeds. Based on genomic in situ hybridization analysis of 261 M1 plants, we identified 74 lines carrying structural aberrations involving chromosome 4J with the higher aberration rate in treated pollen (31.2 %) than in the treated eggs (21.3 %). We further identified 43 (53.8 %) lines with structural aberrations on chromosome 4J by analyzing another 80 M1 plants with 74 4J-specific markers, indicating that combining molecular and cytological methods was more efficient for detecting chromosome aberrations. Marker analysis thus was performed prior to cytogenetic identification on M2-M4 seeds to detect chromosome structural aberrations. Sixty-eight M3 lines with structural aberrations on chromosome 4J and six previously obtained chromosome 4J alien lines were then analyzed using 101 chromosome 4J-specific markers. After combining marker results with chromosome aberrations in each line, chromosome 4J was physically divided into 24 segmental blocks with 7 in the short arm and 17 in the long arm. The blue-grained gene BaThb was further mapped into the region corresponding to block 4JL-11. The chromosome aberrations and the physical map developed in this research provide useful stocks and tools for introgression of genes on chromosome 4J into wheat.

A de novo assembly of genomic dataset sequences of the sugar beet root maggot Tetanops myopaeformis, TmSBRM_v1.0.

The sugar beet root maggot (SBRM), Tetanops myopaeformis (von Röder), is a devastating insect pathogen of sugar beet (SB), Beta vulgaris, ssp vulgaris (B. vulgaris), an important food crop, while also being one of only two plants globally from which sugar is widely produced, and accounting for 35% of global raw sugar with an annual farm value of $3 billion in the United States alone. SBRM is the most devastating pathogen of sugar beet in North America. The limited natural resistance of B. vulgaris necessitates an understanding of the SBRM genome to facilitate generating knowledge of its basic biology, including the interaction between the pathogen and its host(s). Presented is the de novo assembled draft genome sequence of T. myopaeformis isolated from field-grown B. vulgaris in North Dakota, USA. The SBRM genome sequence TmSBRM_v1.0 will also be valuable for molecular genetic marker development to facilitate host resistance gene identification and knowledge, including SB polygalacturonase inhibiting protein (PGIP), and development of new control strategies for this pathogen, relationship to model genetic organisms like Drosophila melanogaster and aid in agronomic improvement of sugar beet for stakeholders while also providing information on the relationship between the SBRM and climate change.

The annotation of genomic dataset sequences of the sugar beet root maggot Tetanops myopaeformis, TmSBRM_v1.0.

Tetanops myopaeformis, the sugar beet root maggot (SBRM), is a devastating insect pathogen of sugar beet, one of only two plants in the world from which sugar is widely produced, accounting for 55% of U.S. sugar and 35% of global raw sugar with an annual farm value of $3 billion in the United States. T. myopaeformis is capable of causing total crop failure, making its study important. The previously released SBRM genome, TmSBRM_v1.0, has been generated from the de novo assembled draft genome sequence of T. myopaeformis isolated that was isolated from field-grown B. vulgaris in North Dakota, USA. The annotation of the T. myopaeformis is presented here. The annotated T. myopaeformis genome should be useful in understanding the biology of this insect and the development of new control strategies for this pathogen, relationship to model genetic organisms like Drosophila melanogaster and aid in agronomic improvement of sugar beet for stakeholders while also providing information on the relationship between the SBRM and climate change.

Genetic drift, historic migration, and limited gene flow contributing to the subpopulation divergence in wild sea beet (Beta vulgaris ssp. maritima (L.) Arcang).

Cultivated beet (Beta vulgaris L. ssp. vulgaris) originated from sea beet (B. vulgaris ssp. maritima (L.) Arcang), a wild beet species widely distributed along the coasts of the Mediterranean Sea and Atlantic Ocean, as well as northern Africa. Understanding the evolution of sea beet will facilitate its efficient use in sugarbeet improvement. We used SNPs (single nucleotide polymorphisms) covering the whole genome to analyze 599 sea beet accessions collected from the north Atlantic Ocean and Mediterranean Sea coasts. All B. maritima accessions can be grouped into eight clusters with each corresponding to a specific geographic region. Clusters 2, 3 and 4 with accessions mainly collected from Mediterranean coasts are genetically close to each other as well as to Cluster 6 that contained mainly cultivated beet. Other clusters were relatively distinct from cultivated beets with Clusters 1 and 5 containing accessions from north Atlantic Ocean coasts, Clusters 7 and Cluster 8 mainly have accessions from northern Egypt and southern Europe, and northwest Morocco, respectively. Distribution of B. maritima subpopulations aligns well with the direction of marine currents that was considered a main dynamic force in spreading B. maritima during evolution. Estimation of genetic diversity indices supported the formation of B. maritima subpopulations due to local genetic drift, historic migration, and limited gene flow. Our results indicated that B. maritima originated from southern Europe and then spread to other regions through marine currents to form subpopulations. This research provides vital information for conserving, collecting, and utilizing wild sea beet to sustain sugarbeet improvement.

Transcriptomic and metabolomic changes in postharvest sugarbeet roots reveal widespread metabolic changes in storage and identify genes potentially responsible for respiratory sucrose loss.

Endogenous metabolism is primarily responsible for losses in sucrose content and processing quality in postharvest sugarbeet roots. The genes responsible for this metabolism and the transcriptional changes that regulate it, however, are largely unknown. To identify genes and metabolic pathways that participate in postharvest sugarbeet root metabolism and the transcriptional changes that contribute to their regulation, transcriptomic and metabolomic profiles were generated for sugarbeet roots at harvest and after 12, 40 and 120 d storage at 5 and 12°C and gene expression and metabolite concentration changes related to storage duration or temperature were identified. During storage, 8656 genes, or 34% of all expressed genes, and 225 metabolites, equivalent to 59% of detected metabolites, were altered in expression or concentration, indicating extensive transcriptional and metabolic changes in stored roots. These genes and metabolites contributed to a wide range of cellular and molecular functions, with carbohydrate metabolism being the function to which the greatest number of genes and metabolites classified. Because respiration has a central role in postharvest metabolism and is largely responsible for sucrose loss in sugarbeet roots, genes and metabolites involved in and correlated to respiration were identified. Seventy-five genes participating in respiration were differentially expressed during storage, including two bidirectional sugar transporter SWEET17 genes that highly correlated with respiration rate. Weighted gene co-expression network analysis identified 1896 additional genes that positively correlated with respiration rate and predicted a pyruvate kinase gene to be a central regulator or biomarker for respiration rate. Overall, these results reveal the extensive and diverse physiological and metabolic changes that occur in stored sugarbeet roots and identify genes with potential roles as regulators or biomarkers for respiratory sucrose loss.

Meta-transcriptomic analysis reveals the geographical expansion of known sugarbeet-infecting viruses and the occurrence of a novel virus in sugarbeet in the United States.

In this study, meta-transcriptome sequencing was conducted on a total of 18 sugarbeet (Beta vulgaris L. subsp. vulgaris) sample libraries to profile the virome of field-grown sugarbeet to identify the occurrence and distribution of known and potentially new viruses from five different states in the United States. Sugarbeet roots with symptoms resembling rhizomania caused by beet necrotic yellow vein virus (BNYVV), or leaves exhibiting leaf-curling, yellowing to browning, or green mosaic were collected from the sugarbeet growing areas of California, Colorado, Idaho, Minnesota, and North Dakota. In silico analysis of de novo assembled contigs revealed the presence of nearly full-length genomes of BNYVV, beet soil-borne virus (BSBV), and beet soil-borne mosaic virus (BSBMV), which represent known sugarbeet-infecting viruses. Among those, BNYVV was widespread across the locations, whereas BSBV was prevalent in Minnesota and Idaho, and BSBMV was only detected in Minnesota. In addition, two recently reported Beta vulgaris satellite virus isoforms (BvSatV-1A and BvSatV-1B) were detected in new locations, indicating the geographical expansion of this known virus. Besides these known sugarbeet-infecting viruses, the bioinformatic analysis identified the widespread occurrence of a new uncharacterized Erysiphe necator-associated abispo virus (En_abispoV), a fungus-related virus that was identified in all 14 libraries. En_abispoV contains two RNA components, and nearly complete sequences of both RNA1 and RNA2 were obtained from RNASeq and were further confirmed by primer-walking RT-PCR and Sanger sequencing. Phylogenetic comparison of En_abispoV isolates obtained in this study showed varying levels of genetic diversity within RNA1 and RNA2 compared to previously reported isolates. The undertaken meta-transcriptomic approach revealed the widespread nature of coexisting viruses associated with field-grown sugarbeet exhibiting virus disease-like symptoms in the United States.

Mechanism of Sugarbeet Seed Germination Enhanced by Hydrogen Peroxide.

Seed germination is a critical first stage of plant development but can be arrested by factors including dormancy and environmental conditions. Strategies to enhance germination are of interest to plant breeders to ensure the ability to utilize the genetic potential residing inside a dormant seed. In this study, seed germination in two sugarbeet (Beta vulgaris ssp. vulgaris L.) lines F1004 and F1015 through incubating seeds in hydrogen peroxide (H2O2) solution was improved over 70% relative to germinating seeds through water incubation. It was further found that low germination from water incubation was caused by physical dormancy in F1015 seeds with initial seed imbibition blocked by the seed pericarp, and physiological dormancy in F1004 seeds with germination compromised due to the physiological condition of the embryo. To identify genes that are differentially expressed in response to cellular activities promoted by H2O2 during overcoming different type of dormancies, an RNA-Seq study was carried out and found H2O2 treatment during germination accelerated the degradation of seed stored mRNAs that were synthesized before or during seed storage to provide protections and maintain the dormant state. Comparison of transcripts in H2O2-treated seeds between the two sugarbeet lines identified differentially expressed genes (DEGs) that were higher in F1004 for alleviating physiological dormancy were known to relative to gene expression regulation. The research established that H2O2 overcomes both physical and physiological dormancies by hastening the transition of seeds from dormancy into germination. More DEGs related to gene expression regulation were involved in relieving physiological dormancy which provides new knowledge about the role of exogenous H2O2 as a signaling molecule for regulating gene activities during germination. Moreover, the protocol using H2O2 to promote germination will be useful for rescuing plant germplasms with poor germination.

Development of the Wheat Practical Haplotype Graph database as a resource for genotyping data storage and genotype imputation.

To improve the efficiency of high-density genotype data storage and imputation in bread wheat (Triticum aestivum L.), we applied the Practical Haplotype Graph (PHG) tool. The Wheat PHG database was built using whole-exome capture sequencing data from a diverse set of 65 wheat accessions. Population haplotypes were inferred for the reference genome intervals defined by the boundaries of the high-quality gene models. Missing genotypes in the inference panels, composed of wheat cultivars or recombinant inbred lines genotyped by exome capture, genotyping-by-sequencing (GBS), or whole-genome skim-seq sequencing approaches, were imputed using the Wheat PHG database. Though imputation accuracy varied depending on the method of sequencing and coverage depth, we found 92% imputation accuracy with 0.01× sequence coverage, which was slightly lower than the accuracy obtained using the 0.5× sequence coverage (96.6%). Compared to Beagle, on average, PHG imputation was ∼3.5% (P-value < 2 × 10-14) more accurate, and showed 27% higher accuracy at imputing a rare haplotype introgressed from a wild relative into wheat. We found reduced accuracy of imputation with independent 2× GBS data (88.6%), which increases to 89.2% with the inclusion of parental haplotypes in the database. The accuracy reduction with GBS is likely associated with the small overlap between GBS markers and the exome capture dataset, which was used for constructing PHG. The highest imputation accuracy was obtained with exome capture for the wheat D genome, which also showed the highest levels of linkage disequilibrium and proportion of identity-by-descent regions among accessions in the PHG database. We demonstrate that genetic mapping based on genotypes imputed using PHG identifies SNPs with a broader range of effect sizes that together explain a higher proportion of genetic variance for heading date and meiotic crossover rate compared to previous studies.