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PLOS ONE: Genome-Wide Association Mapping of Root Traits in a Japonica Rice Panel

Rice is a crop prone to drought stress in upland and rainfed lowland ecosystems. A deep root system is recognized as the best drought avoidance mechanism. Genome-wide association mapping offers higher resolution for locating quantitative trait loci (QTLs) than QTL mapping in biparental populations. We performed an association mapping study for root traits using a panel of 167 japonica accessions, mostly of tropical origin. The panel was genotyped at an average density of one marker per 22.5 kb using genotyping by sequencing technology. The linkage disequilibrium in the panel was high (r2>0.6, on average, for 20 kb mean distances between markers). The plants were grown in transparent 50 cm × 20 cm × 2 cm Plexiglas nailboard sandwiches filled with 1.5 mm glass beads through which a nutrient solution was circulated. Root system architecture and biomass traits were measured in 30-day-old plants. The panel showed a moderate to high diversity in the various traits, particularly for deep (below 30 cm depth) root mass and the number of deep roots. Association analyses were conducted using a mixed model involving both population structure and kinship to control for false positives. Nineteen associations were significant at P<1e-05, and 78 were significant at P<1e-04. The greatest numbers of significant associations were detected for deep root mass and the number of deep roots, whereas no significant associations were found for total root biomass or deep root proportion. Because several QTLs for different traits were co-localized, 51 unique loci were detected; several co-localized with meta-QTLs for root traits, but none co-localized with rice genes known to be involved in root growth. Several likely candidate genes were found in close proximity to these loci. Additional work is necessary to assess whether these markers are relevant in other backgrounds and whether the genes identified are robust candidates.
 
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Upcoming Webinar: Lattice Designs - eXtension

Upcoming Webinar: Lattice Designs - eXtension | Plant Breeding and Genomics News | Scoop.it

Jennifer Kling will describe the layout and analysis of lattice field designs.Thursday November 14, 2013 at 1:00 pm EDT. Register now https://www1.gotomeeting.com/register/790644664

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Protecting the weedy and wild kin of globally important crops

Protecting the weedy and wild kin of globally important crops | Plant Breeding and Genomics News | Scoop.it

On Wednesday, Nov. 6, 2013, two speakers will describe the latest efforts to identify and protect the wild relatives of domesticated crop plants around the globe. The presentations are part of the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Soil Science Society of America (SSSA) International Annual Meetings, Nov. 3-6 in Tampa, Florida.

Plant Breeding and Genomics News's insight:

Members of the American Society of Agronomy, Crop Science Society of America, and the Soil Science Society of American can livestream many of the upcoming talks.  Register to livestream 

https://scisoc.confex.com/crops/2013am/webprogram/Session11639.html

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Development and evaluation of a field-based high-throughput phenotyping platform

Development and evaluation of a field-based high-throughput phenotyping platform | Plant Breeding and Genomics News | Scoop.it

Physiological and developmental traits that vary over time are difficult to phenotype under relevant growing conditions. In this light, we developed a novel system for phenotyping dynamic traits in the field. System performance was evaluated on 25 Pima cotton (Gossypium barbadense L.) cultivars grown in 2011 at Maricopa, Arizona. Field-grown plants were irrigated under well watered and water-limited conditions, with measurements taken at different times on 3 days in July and August. The system carried four sets of sensors to measure canopy height, reflectance and temperature simultaneously on four adjacent rows, enabling the collection of phenotypic data at a rate of 0.84 ha h–1. Measurements of canopy height, normalised difference vegetation index and temperature all showed large differences among cultivars and expected interactions of cultivars with water regime and time of day. Broad-sense heritabilities (H2)were highest for canopy height (H2 = 0.86–0.96), followed by the more environmentally sensitive normalised difference vegetation index (H2 = 0.28–0.90) and temperature (H2 = 0.01–0.90) traits. We also found a strong agreement (r2 = 0.35–0.82) between values obtained by the system, and values from aerial imagery and manual phenotyping approaches. Taken together, these results confirmed the ability of the phenotyping system to measure multiple traits rapidly and accurately.

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Variation in Contents of Main Active Components and Antioxidant Activity in Leaves of Different Pigeon Pea Cultivars during Growth - Journal of Agricultural and Food Chemistry (ACS Publications)

Variation in Contents of Main Active Components and Antioxidant Activity in Leaves of Different Pigeon Pea Cultivars during Growth - Journal of Agricultural and Food Chemistry (ACS Publications) | Plant Breeding and Genomics News | Scoop.it

Pigeon pea is an important and multiuse grain legume crop, and its leaves are a very valuable natural resource. To obtain a high-quality biological resource, it is necessary to choose the excellent cultivar and determine the appropriate harvest time. In this study, the variation in contents of main active components and antioxidant activity in leaves of six pigeon pea cultivars during growth were investigated. The level of each individual active component significantly varied during growth, but with a different pattern, and this variation was different among cultivars. Flavonoid glycosides orientin, vitexin, and apigenin-6,8-di-C-α-l-arabinopyranoside showed two peak values at mid-late and final stages of growth in most cases. Pinostrobin chalcone, longistyline C, and cajaninstilbene acid showed remarkablely higher values at the mid-late stage of growth than at other stages. Pinostrobin had an extremely different variation pattern compared to other active components. Its content was the highest at the earlier stage of growth. Principal component analysis (PCA) revealed that vitexin and apigenin-6,8-di-C-α-l-arabinopyranoside were mainly responsible for distinguishing cultivars analyzed. In a comprehensive consideration, the leaves should preferentially be harvested at the 135th day after sowing when the level of active components and antioxidant activity reached higher values. Cultivars ICP 13092, ICPL 87091, and ICPL 96053 were considered to be excellent cultivars with high antioxidant activity. Our findings can provide valuable information for producing a high-quality pigeon pea resource.

 
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Trends in Plant Science - Field high-throughput phenotyping: the new crop breeding frontier

Constraints in field phenotyping capability limit our ability to dissect the genetics of quantitative traits, particularly those related to yield and stress tolerance (e.g., yield potential as well as increased drought, heat tolerance, and nutrient efficiency, etc.). The development of effective field-based high-throughput phenotyping platforms (HTPPs) remains a bottleneck for future breeding advances. However, progress in sensors, aeronautics, and high-performance computing are paving the way. Here, we review recent advances in field HTPPs, which should combine at an affordable cost, high capacity for data recording, scoring and processing, and non-invasive remote sensing methods, together with automated environmental data collection. Laboratory analyses of key plant parts may complement direct phenotyping under field conditions. Improvements in user-friendly data management together with a more powerful interpretation of results should increase the use of field HTPPs, therefore increasing the efficiency of crop genetic improvement to meet the needs of future generations.

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Generation, functional annotation and comparative analysis of black spruce ESTs: an important conifer genomic resource

EST (expressed sequence tag) sequences and their annotation provide a highly valuable resource for gene discovery, genome sequence annotation, and other genomics studies that can be applied in genetics, breeding and conservation programs for...
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BMC Plant Biology | Abstract | PT-Flax (phenotyping and TILLinG of flax): development of a flax (Linum usitatissimum L.) mutant population and TILLinG platform for forward and reverse genetics

Background: Flax (Linum usitatissimum L.) is an economically important fiber and oil crop that has been grown for thousands of years. The genome has been recently sequenced and transcriptomics are providing information on candidate genes potentially related to agronomically-important traits. In order to accelerate functional characterization of these genes we have generated a flax EMS mutant population that can be used as a TILLinG (Targeting Induced Local Lesions in Genomes) platform for forward and reverse genetics. Results: A population of 4,894 M2 mutant seed families was generated using 3 different EMS concentrations (0.3%, 0.6% and 0.75%) and used to produce M2 plants for subsequent phenotyping and DNA extraction. 10,839 viable M2 plants (4,033 families) were obtained and 1,552 families (38.5%) showed a visual developmental phenotype (stem size and diameter, plant architecture, flower-related). The majority of these families showed more than one phenotype. Mutant phenotype data are organised in a database and can be accessed and searched at UTILLdb (http://urgv.evry.inra.fr/UTILLdb). Preliminary screens were also performed for atypical fiber and seed phenotypes. Genomic DNA was extracted from 3,515 M2 families and eight-fold pooled for subsequent mutant detection by ENDO1 nuclease mis-match cleavage. In order to validate the collection for reverse genetics, DNA pools were screened for two genes coding enzymes of the lignin biosynthesis pathway: Coumarate-3-Hydroxylase (C3H) and Cinnamyl Alcohol Dehydrogenase (CAD). We identified 79 and 76 mutations in the C3H and CAD genes, respectively. The average mutation rate was calculated as 1/41Kb giving rise to approximately 9,000 mutations per genome. Thirty-five out of the 52 flax cad mutant families containing missense or codon stop mutations showed the typical orange-brown xylem phenotype observed in CAD down-regulated/mutant plants in other species. Conclusions: We have developed a flax mutant population that can be used as an efficient forward and reverse genetics tool. The collection has an extremely high mutation rate that enables the detection of large numbers of independant mutant families by screening a comparatively low number of M2 families. The population will prove to be a valuable resource for both fundamental research and the identification of agronomically-important genes for crop improvement in flax.  
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Synthetic nucleases for genome engineering in plants: prospects for a bright future - Puchta - The Plant Journal - Wiley Online Library

Synthetic nucleases for genome engineering in plants: prospects for a bright future - Puchta - The Plant Journal - Wiley Online Library | Plant Breeding and Genomics News | Scoop.it

By inducing double-strand breaks (DSB), it is possible to initiate DNA recombination. For a long time, it was not possible to use DSB induction for efficient genome engineering due to the lack of a way to target DSBs to specific sites. With the development of modified meganucleases and synthetic DNA binding domains, this limitation was overcome. Domains derived from zinc finger transcription factors or transcription activator-like effectors can be designed to recognise almost any DNA sequence. By fusing these domains to the endonuclease domains of a class II restriction enzyme, an active endonuclease dimer can be formed that introduces a site-specific DSB. Recent studies demonstrate that gene knock-outs via nonhomologous end joining or gene modification via homologous recombination are becoming routine in many plant species. By setting a single genomic DSB, the complete knock-out of a gene, the sequence-specific integration of foreign DNA, or the subtle modification of individual amino acids in a specific protein domain can be achieved. The induction of two or more DSBs allows for complex genomic rearrangements such as deletions, inversions, or the exchange of chromosome arms. The potential of controlled genome engineering in plants is tremendous. The recently discovered RNA-based CRISPR/Cas9 system as new tool to induce multiple DSBs or sophisticated technical applications, such as the in planta gene targeting system, are further steps in this development. At the moment, the focus still lies on the engineering of single genes; in the future, the engineering of whole genomes will become an option. This article is protected by copyright. All rights reserved.

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PLOS ONE: QTL Mapping of Leafy Heads by Genome Resequencing in the RIL Population of Brassica rapa

PLOS ONE: QTL Mapping of Leafy Heads by Genome Resequencing in the RIL Population of Brassica rapa | Plant Breeding and Genomics News | Scoop.it

Leaf heads of cabbage (Brassica oleracea), Chinese cabbage (B. rapa), and lettuce (Lactuca sativa) are important vegetables that supply mineral nutrients, crude fiber and vitamins in the human diet. Head size, head shape, head weight, and heading time contribute to yield and quality. In an attempt to investigate genetic basis of leafy head in Chinese cabbage (B. rapa), we took advantage of recent technical advances of genome resequencing to perform quantitative trait locus (QTL) mapping using 150 recombinant inbred lines (RILs) derived from the cross between heading and non-heading Chinese cabbage. The resequenced genomes of the parents uncovered more than 1 million SNPs. Genotyping of RILs using the high-quality SNPs assisted by Hidden Markov Model (HMM) generated a recombination map. The raw genetic map revealed some physical assembly error and missing fragments in the reference genome that reduced the quality of SNP genotyping. By deletion of the genetic markers in which recombination rates higher than 20%, we have obtained a high-quality genetic map with 2209 markers and detected 18 QTLs for 6 head traits, from which 3 candidate genes were selected. These QTLs provide the foundation for study of genetic basis of leafy heads and the other complex traits.

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High genome heterozygosity and endemic genetic recombination in the wheat stripe rust fungus : Nature Communications : Nature Publishing Group

High genome heterozygosity and endemic genetic recombination in the wheat stripe rust fungus : Nature Communications : Nature Publishing Group | Plant Breeding and Genomics News | Scoop.it

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases of wheat. Here we report a 110-Mb draft sequence of Pst isolate CY32, obtained using a ‘fosmid-to-fosmid’ strategy, to better understand its race evolution and pathogenesis. The Pst genome is highly heterozygous and contains 25,288 protein-coding genes. Compared with non-obligate fungal pathogens, Pst has a more diverse gene composition and more genes encoding secreted proteins. Re-sequencing analysis indicates significant genetic variation among six isolates collected from different continents. Approximately 35% of SNPs are in the coding sequence regions, and half of them are non-synonymous. High genetic diversity in Pst suggests that sexual reproduction has an important role in the origin of different regional races. Our results show the effectiveness of the ‘fosmid-to-fosmid’ strategy for sequencing dikaryotic genomes and the feasibility of genome analysis to understand race evolution in Pst and other obligate pathogens.

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Could abiotic stress tolerance in wild relatives of rice be used to improve Oryza sativa?

Could abiotic stress tolerance in wild relatives of rice be used to improve Oryza sativa? | Plant Breeding and Genomics News | Scoop.it
Abstract

Oryza sativa and O. glaberrima have been selected to acquire and partition resources efficiently as part of the process of domestication. However, genetic diversity in cultivated rice is limited compared to wild Oryzaspecies, in spite of 120,000 genotypes being held in gene banks. By contrast, there is untapped diversity in the more than 20 wild species of Oryza, some having been collected from just a few coastal locations (e.g.O. schlechteri), while others are widely distributed (e.g. O. nivara and O. rufipogon). The extent of DNA sequence diversity and phenotypic variation is still being established in wild Oryza, with genetic barriers suggesting a vast range of morphologies and function even within species, such as has been demonstrated for O. meridionalis. With increasing climate variability and attempts to make more marginal land arable, abiotic and biotic stresses will be managed over the coming decades by tapping into the genetic diversity of wild relatives of O. sativa. To help create a more targeted approach to sourcing wild rice germplasm for abiotic stress tolerance, we have created a climate distribution map by plotting the natural occurrence of allOryza species against corresponding temperature and moisture data. We then discuss interspecific variation in phenotype and its significance for rice, followed by a discussion of ways to integrate germplasm from wild relatives into domesticated rice.

  
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Adaptation and exogenous selection in a Picea glauca × Picea engelmannii hybrid zone: implications for forest management under climate change

Adaptation and exogenous selection in a Picea glauca × Picea engelmannii hybrid zone: implications for forest management under climate change | Plant Breeding and Genomics News | Scoop.it
The nature of selection responsible for the maintenance of the economically and ecologically important Picea glauca × Picea engelmannii hybrid zone was investigated. Genomic, phenotypic and climatic data were used to test assumptions of hybrid zone maintenance and to model future scenarios under climate change.Genome-wide estimates of admixture based on a panel of 86 candidate gene single nucleotide polymorphisms were combined with long-term quantitative data on growth and survival (over 20 yr), as well as one-time assessments of bud burst and bud set phenology, and cold hardiness traits. A total of 15 498 individuals were phenotyped for growth and survival.Our results suggest that the P. glauca × P. engelmannii hybrid zone is maintained by local adaptation to growing season length and snowpack (exogenous selection). Hybrids appeared to be fitter than pure species in intermediate environments, which fits expectations of the bounded hybrid superiority model of hybrid zone maintenance. Adaptive introgression from parental species has probably contributed to increased hybrid fitness in intermediate habitats.While P. engelmannii ancestry is higher than P. glauca ancestry in hybrid populations, on average, selective breeding in managed hybrid populations is shifting genomic composition towards P. glauca, potentially pre-adapting managed populations to warmer climates.
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Shawn Yarnes, the PBG Content Coordinator, is Leaving to join the Generation Challenge Program's Integrated Breeding Platform

Shawn Yarnes, the PBG Content Coordinator,  is Leaving to join the Generation Challenge Program's Integrated Breeding Platform | Plant Breeding and Genomics News | Scoop.it

My time with the Plant Breeding and Genomics Community of Practice on eXtension.org has been a fantastic opportunity to see plant breeding from a multi-crop and multi-trait perspective.  It has been a privilege to be involved in plant breeding extension through the development of open-source tutorials (http://www.extension.org/plant_breeding_genomics) and Plant Breeding and Genomics News (http://www.scoop.it/t/plant-breeding-and-genomics-news). I look forward to applying this experience in my new position as Genotyping Support Scientist with the Generation Challenge Program. Thank you to everyone who contributes to the Plant Breeding Community of Practice.

 

Sincerely,

Shawn Yarnes 

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Breeding with Genomics Course in Davis, CA Feb 11-13th, 2014.

Breeding with Genomics Course in Davis, CA Feb 11-13th, 2014. | Plant Breeding and Genomics News | Scoop.it

Program
The course covers the basics of DNA markers, quantitative trait loci and the transition from maker assisted selection with a highlight on breeding for disease resistance.


New for 2014!
Extended modules on genomic selection, the latest integration of genomics to breeding, and a hands-on workshop on software support to marker application in breeding including the Integrated Breeding Platform and BLUPS.


Who should attend?
The course is aimed at professionals who are directly or indirectly involved in plant breeding and germplasm improvement.  It is an opportunity for breeders who are already using these tools to expand their knowledge of new strategies and technologies and for laboratory personnel to appreciate how the marker data that they generate are applied in breeding programs.

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Use of introgression lines to determine the ecophysiological basis for changes in water use efficiency and yield in California processing tomatoes

Field and greenhouse studies examined the effects of growth habit and chloroplast presence in leaf veins for their role in increasing agronomic water use efficiency and yields of California modern processing tomato (Solanum lycopersicum L.) cultivars. Five introgression lines (ILs), made with Solanum pennellii Cor. in the genetic background of cultivar M82, differ in genes that map to a region on Chromosome 5, including the SP5G gene (determinate vs. semideterminate (Det vs. SemiDet)) and the obv gene (presence (obscure) vs. absence (clear) of leaf vein chloroplasts (Obs vs. Clr)). The five ILs and M82 represented three of the four gene combinations (Det–Clr was unavailable). Det–Obs ILs had less leaf, stem and total aboveground biomass with earlier fruit set and ripening than SemiDet–Clr ILs. By harvest, total fruit biomass was not different among ILs. Photosynthetic rates and stomatal conductance were 4–7% and 13–26% higher, respectively, in Det–Obs ILs than SemiDet–Clr ILs. SemiDet–Obs ILs were intermediate for growth and gas exchange variables. The Det–Obs ILs had lower leaf N concentration and similar chlorophyll content per leaf area (but slightly higher per leaf mass) than SemiDet–Clr ILs. The Obs trait was associated with gains in leaf gas exchange-related traits. This study suggests that a more compact growth habit, less leaf biomass and higher C assimilation capacity per leaf area were relevant traits for the increased yields in cultivars with determinate growth. Developing new introgression libraries would contribute to understanding the multiple trait effects of desirable phenotypes.

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BMC Plant Biology | Abstract | Identification and fine-mapping of a QTL, qMrdd1, that confers recessive resistance to maize rough dwarf disease

Background

Maize rough dwarf disease (MRDD) is a devastating viral disease that results in considerable yield losses worldwide. Three major strains of virus cause MRDD, including maize rough dwarf virus in Europe, Mal de Rio Cuarto virus in South America, and rice black-streaked dwarf virus in East Asia. These viral pathogens belong to the genus fijivirus in the family Reoviridae. Resistance against MRDD is a complex trait that involves a number of quantitative trait loci (QTL). The primary approach used to minimize yield losses from these viruses is to breed and deploy resistant maize hybrids.

Results

Of the 50 heterogeneous inbred families (HIFs), 24 showed consistent responses to MRDD across different years and locations, in which 9 were resistant and 15 were susceptible. We performed trait-marker association analysis on the 24 HIFs and found six chromosomal regions which were putatively associated with MRDD resistance. We then conducted QTL analysis and detected a major resistance QTL, qMrdd1, on chromosome 8. By applying recombinant-derived progeny testing to self-pollinated backcrossed families, we fine-mapped the qMrdd1 locus into a 1.2-Mb region flanked by markers M103-4 and M105-3. The qMrdd1 locus acted in a recessive manner to reduce the disease-severity index (DSI) by 24.2--39.3%. The genetic effect of qMrdd1 was validated using another F6 recombinant inbred line (RIL) population in which MRDD resistance was segregating and two genotypes at the qMrdd1 locus differed significantly in DSI values.

Conclusions

The qMrdd1 locus is a major resistance QTL, acting in a recessive manner to increase maize resistance to MRDD. We mapped qMrdd1 to a 1.2-Mb region, which will enable the introgression of qMrdd1-based resistance into elite maize hybrids and reduce MRDD-related crop losses.

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BMC Biotechnology | Abstract | Development of selectable marker free, insect resistant, transgenic mustard (Brassica juncea) plants using Cre/lox mediated recombination

Background: Radish (Raphanus sativus L., 2n = 2x = 18) is an economically important vegetable crop worldwide. A large collection of radish expressed sequence tags (ESTs) has been generated but remains largely uncharacterized. Results: In this study, approximately 315,000 ESTs derived from 22 Raphanus cDNA libraries from 18 different genotypes were analyzed, for the purpose of gene and marker discovery and to evaluate large-scale genome duplication and phylogenetic relationships among Raphanus spp. The ESTs were assembled into 85,083 unigenes, of which 90%, 65%, 89% and 89% had homologous sequences in the GenBank nr, SwissProt, TrEMBL and Arabidopsis protein databases, respectively. A total of 66,194 (78%) could be assigned at least one gene ontology (GO) term. Comparative analysis identified 5,595 gene families unique to radish that were significantly enriched with genes related to small molecule metabolism, as well as 12,899 specific to the Brassicaceae that were enriched with genes related to seed oil body biogenesis and responses to phytohormones. The analysis further indicated that the divergence of radish and Brassica rapa occurred approximately 8.9-14.9 million years ago (MYA), following a whole-genome duplication event (12.8-21.4 MYA) in their common ancestor. An additional whole-genome duplication event in radish occurred at 5.1-8.4 MYA, after its divergence from B. rapa. A total of 13,570 simple sequence repeats (SSRs) and 28,758 high-quality single nucleotide polymorphisms (SNPs) were also identified. Using a subset of SNPs, the phylogenetic relationships of eight different accessions of Raphanus was inferred. Conclusion: Comprehensive analysis of radish ESTs provided new insights into radish genome evolution and the phylogenetic relationships of different radish accessions. Moreover, the radish EST sequences and the associated SSR and SNP markers described in this study represent a valuable resource for radish functional genomics studies and breeding.

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Virginia Garreton's curator insight, November 4, 2013 3:01 PM

New technology to accelerate the selection of genetic markers relevant to plant selection

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BMC Genomics | Abstract | Quantitative trait loci-dependent analysis of a gene co-expression network associated with Fusarium head blight resistance in bread wheat (Triticum aestivum L.)

Background: Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe is one of the most prevalent diseases of wheat (Triticum aestivum L.) and other small grain cereals. Resistance against the fungus is quantitative and more than 100 quantitative trait loci (QTL) have been described. Two well-validated and highly reproducible QTL, Fhb1 and Qfhs.ifa-5A have been widely investigated, but to date the underlying genes have not been identified. Results: We have investigated a gene co-expression network activated in response to F. graminearum using RNA-seq data from near-isogenic lines, harboring either the resistant or the susceptible allele for Fhb1 and Qfhs.ifa-5A. The network identified pathogen-responsive modules, which were enriched for differentially expressed genes between genotypes or different time points after inoculation with the pathogen. Central gene analysis identified transcripts associated with either QTL within the network. Moreover, we present a detailed gene expression analysis of four gene families (glucanases, NBS-LRR, WRKY transcription factors and UDP-glycosyltransferases), which take prominent roles in the pathogen response. Conclusions: A combination of a network-driven approach and differential gene expression analysis identified genes and pathways associated with Fhb1 and Qfhs.ifa-5A. We find G-protein coupled receptor kinases and biosynthesis genes for jasmonate and ethylene earlier induced for Fhb1. Similarly, we find genes involved in the biosynthesis and metabolism of riboflavin more abundant for Qfhs.ifa-5A.

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BMC Plant Biology | Abstract | Fine mapping and identification of a candidate gene for a major locus controlling maturity date in peach

Background

Maturity date is a crucial factor for marketing of fresh fruit, especially those with limited shelf-life such as peach (Prunus persica L. Batsch): selection of several cultivars with differing MD would be advantageous to cover and extend the marketing season. Aims of this work were the fine mapping and identification of candidate genes for the major maturity date locus previously identified on peach linkage group 4. To improve genetic resolution of the target locus two F2 populations derived from the crosses Contender x Ambra (CxA, 306 individuals) and PI91459 (NJ Weeping) x Bounty (WxBy, 103 individuals) were genotyped with the Sequenom and 9K Illumina Peach Chip SNP platforms, respectively.

Results

Recombinant individuals from the WxBy F2 population allowed the localisation of maturity date locus to a 220 kb region of the peach genome. Among the 25 annotated genes within this interval, functional classification identified ppa007577m and ppa008301m as the most likely candidates, both encoding transcription factors of the NAC (NAM/ATAF1, 2/CUC2) family. Re-sequencing of the four parents and comparison with the reference genome sequence uncovered a deletion of 232 bp in the upstream region of ppa007577m that is homozygous in NJ Weeping and heterozygous in Ambra, Bounty and the WxBy F1 parent. However, this variation did not segregate in the CxA F2 population being the CxA F1 parent homozygous for the reference allele. The second gene was thus examined as a candidate for maturity date. Re-sequencing of ppa008301m, showed an in-frame insertion of 9 bp in the last exon that co-segregated with the maturity date locus in both CxA and WxBy F2 populations.

Conclusions

Using two different segregating populations, the map position of the maturity date locus was refined from 3.56 Mb to 220 kb. A sequence variant in the NAC gene ppa008301m was shown to co-segregate with the maturity date locus, suggesting this gene as a candidate controlling ripening time in peach. If confirmed on other genetic materials, this variant may be used for marker-assisted breeding of new cultivars with differing maturity date.

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BMC Plant Biology | Abstract | Identification of mildew resistance in wild and cultivated Central Asian grape germplasm

Background: Cultivated grapevines, Vitis vinifera subsp. sativa, evolved from their wild relative, V. vinifera subsp. sylvestris. They were domesticated in Central Asia in the absence of the powdery mildew fungus, Erysiphe necator, which is thought to have originated in North America. However, powdery mildew resistance has previously been discovered in two Central Asian cultivars and in Chinese Vitis species. Results: A set of 380 unique genotypes were evaluated with data generated from 34 simple sequence repeat (SSR) markers. The set included 306 V. vinifera cultivars, 40 accessions of V. vinifera subsp. sylvestris, and 34 accessions of Vitis species from northern Pakistan, Afghanistan and China. Based on the presence of four SSR alleles previously identified as linked to the powdery mildew resistance locus, Ren1, 10 new mildew resistant genotypes were identified in the test set: eight were V. vinifera cultivars and two were V. vinifera subsp. sylvestris based on flower and seed morphology. Sequence comparison of a 620 bp region that includes the Ren1-linked allele (143 bp) of the co-segregating SSR marker SC8-0071-014, revealed that the ten newly identified genotypes have sequences that are essentially identical to the previously identified mildew resistant V. vinifera cultivars: 'Kishmish vatkana' and 'Karadzhandal'. Kinship analysis determined that three of the newly identified powdery mildew resistant accessions had a relationship with 'Kishmish vatkana' and 'Karadzhandal', and that six were not related to any other accession in this study set. Clustering procedures assigned accessions into three groups: 1) Chinese species; 2) a mixed group of cultivated and wild V. vinifera; and 3) table grape cultivars, including nine of the powdery mildew resistant accessions. Gene flow was detected among the groups. Conclusions: This study provides evidence that powdery mildew resistance is present in V. vinifera subsp. sylvestris, the dioecious wild progenitor of the cultivated grape. Four first-degree parent progeny relationships were discovered among the hermaphroditic powdery mildew resistant cultivars, supporting the existence of intentional grape breeding efforts. Although several Chinese grape species are resistant to powdery mildew, no direct genetic link to the resistance found in V. vinifera could be established.

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Estimating inbreeding coefficients from NGS data: Impact on genotype calling and allele frequency estimation

Most methods for next-generation sequencing (NGS) data analyses incorporate information regarding allele frequencies using the assumption of Hardy–Weinberg equilibrium (HWE) as a prior. However, many organisms including those that are domesticated, partially selfing, or with asexual life cycles show strong deviations from HWE. For such species, and specially for low-coverage data, it is necessary to obtain estimates of inbreeding coefficients (F) for each individual before calling genotypes. Here, we present two methods for estimating inbreeding coefficients from NGS data based on an expectation-maximization (EM) algorithm. We assess the impact of taking inbreeding into account when calling genotypes or estimating the site frequency spectrum (SFS), and demonstrate a marked increase in accuracy on low-coverage highly inbred samples. We demonstrate the applicability and efficacy of these methods in both simulated and real data sets.

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PLOS ONE: A New Fungal Endophyte, Scolecobasidium humicola, Promotes Tomato Growth under Organic Nitrogen Conditions

PLOS ONE: A New Fungal Endophyte, Scolecobasidium humicola, Promotes Tomato Growth under Organic Nitrogen Conditions | Plant Breeding and Genomics News | Scoop.it

A new fungal endophyte, Scolecobasidium humicola, was identified as a common dark septate endophytic fungal (DSE) species under both natural and agricultural conditions. This fungus was found to grow endophylically in the roots of tomato seedlings. Light microscopy of cross-sections of colonized tomato roots showed that the intercellular, pigmented hyphae of the fungus were mostly limited to the epidermal layer and formed outer mantle-like structures. Two isolates of S. humicola, H2-2 and F1-3, have shown the ability to increase plant biomass with an organic nitrogen source. This finding is the first report of S. humicola as an endophyte and could help to improve plant growth with organic nitrogen sources.

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PLOS ONE: Weed Mapping in Early-Season Maize Fields Using Object-Based Analysis of Unmanned Aerial Vehicle (UAV) Images

PLOS ONE: Weed Mapping in Early-Season Maize Fields Using Object-Based Analysis of Unmanned Aerial Vehicle (UAV) Images | Plant Breeding and Genomics News | Scoop.it

The use of remote imagery captured by unmanned aerial vehicles (UAV) has tremendous potential for designing detailed site-specific weed control treatments in early post-emergence, which have not possible previously with conventional airborne or satellite images. A robust and entirely automatic object-based image analysis (OBIA) procedure was developed on a series of UAV images using a six-band multispectral camera (visible and near-infrared range) with the ultimate objective of generating a weed map in an experimental maize field in Spain. The OBIA procedure combines several contextual, hierarchical and object-based features and consists of three consecutive phases: 1) classification of crop rows by application of a dynamic and auto-adaptive classification approach, 2) discrimination of crops and weeds on the basis of their relative positions with reference to the crop rows, and 3) generation of a weed infestation map in a grid structure. The estimation of weed coverage from the image analysis yielded satisfactory results. The relationship of estimated versus observed weed densities had a coefficient of determination of r2=0.89 and a root mean square error of 0.02. A map of three categories of weed coverage was produced with 86% of overall accuracy. In the experimental field, the area free of weeds was 23%, and the area with low weed coverage (<5% weeds) was 47%, which indicated a high potential for reducing herbicide application or other weed operations. The OBIA procedure computes multiple data and statistics derived from the classification outputs, which permits calculation of herbicide requirements and estimation of the overall cost of weed management operations in advance.

  
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PLOS ONE: Drought Responses of Foliar Metabolites in Three Maize Hybrids Differing in Water Stress Tolerance

PLOS ONE: Drought Responses of Foliar Metabolites in Three Maize Hybrids Differing in Water Stress Tolerance | Plant Breeding and Genomics News | Scoop.it

Maize (Zea mays L.) hybrids varying in drought tolerance were treated with water stress in controlled environments. Experiments were performed during vegetative growth and water was withheld for 19 days beginning 17 days after sowing. Genotypic comparisons used measured changes of leaf water potential or results were expressed by time of treatment. Total dry matter of the drought tolerant hybrid on the final harvest was 53% less than that of the intermediate and susceptible maize hybrids when plants were water sufficient. This showed that maize hybrids selected for extreme drought tolerance possessed a dwarf phenotype that affected soil water contents and leaf water potentials. Changes of shoot and root growth, leaf water potential, net photosynthesis and stomatal conductance in response to the time of water stress treatment were diminished when comparing the drought tolerant to the intermediate or susceptible maize hybrids. Genotypic differences were observed in 26 of 40 total foliar metabolites during water stress treatments. Hierarchical clustering revealed that the tolerant maize hybrid initiated the accumulation of stress related metabolites at higher leaf water potentials than either the susceptible or intermediate hybrids. Opposite results occurred when changes of metabolites in maize leaves were expressed temporally. The above results demonstrated that genotypic differences were readily observed by comparing maize hybrids differing in drought tolerance based on either time of treatment or measured leaf water potential. Current findings provided new and potentially important insights into the mechanisms of drought tolerance in maize.

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