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Introduction: Ascochyta blight (AB) caused by the necrotrophic fungus Ascochyta rabiei is one of the most significant diseases that limit the production of chickpea. Understanding the metabolic mechanisms underlying chickpea-A.rabiei interactions will provide important clues to develop novel approaches to manage this disease. Methods: We performed metabolite profiling of the aerial tissue (leaf and stem) of two chickpea accessions comprising a moderately resistant breeding line (CICA1841) and a highly susceptible cultivar (Kyabra) in response to one of the highly aggressive Australian A. rabiei isolates TR9571 via non-targeted metabolomics analysis using liquid chromatography-mass spectrometry. Results: The results revealed resistance and susceptibility-associated constitutive metabolites for example the moderately resistant breeding line had a higher mass abundance of ferulic acid while the levels of catechins, phthalic acid, and nicotinic acid were high in the susceptible cultivar. Further, the host-pathogen interaction resulted in the altered levels of various metabolites (induced and suppressed), especially in the susceptible cultivar revealing a possible reason for susceptibility against A.r abiei. Noticeably, themass abundance of salicylic acid was induced in the aerial tissue of the susceptible cultivar after fungus colonization, while methyl jasmonate (MeJA) was suppressed, elucidating the key role of phytohormones in chickpea-A. rabiei interaction. Many differential metabolites in flavonoid biosynthesis, phenylalanine, Aminoacyl-tRNA biosynthesis, pentose and glucuronate interconversions, arginine biosynthesis, valine, leucine, and isoleucine biosynthesis, and alanine, aspartate, and glutamate metabolism pathways were upand down-regulated showing the involvement of these metabolic pathways in chickpea-A. rabiei interaction. Discussion: Taken together, this study highlights the chickpea -- A. rabiei interaction at a metabolite level and shows how A. rabiei differentially alters the metabolite profile ofmoderately resistant and susceptible chickpea accessions and is probably exploiting the chickpea defense pathways in its favour. [ABSTRACT FROM AUTHOR]

Acid soils limit yields of many important crops including canola (Brassica napus), Australia’s third largest crop. Aluminium (Al3+) stress is the main cause of this limitation primarily because the toxic Al3+ present inhibits root growth. Breeding programmes do not target acid-soil tolerance in B. napus because genetic variation and convincing quantitative trait loci have not been reported. We conducted a genome-wide association study (GWAS) using the BnASSYST diversity panel of B. napus genotyped with 35 729 high-quality DArTseq markers. We screened 352 B. napus accessions in hydroponics with and without a toxic concentration of AlCl3 (12 μM, pH 4.3) for 12 days and measured shoot biomass, root biomass, and root length. By accounting for both population structure and kinship matrices, five significant quantitative trait loci for different measures of resistance were identified using incremental Al3+ resistance indices. Within these quantitative trait locus regions of B. napus, 40 Arabidopsis thaliana gene orthologues were identified, including some previously linked with Al3+ resistance. GWAS analysis indicated that multiple genes are responsible for the natural variation in Al3+ resistance in B. napus. The results provide new genetic resources and markers to enhance that Al3+ resistance of B. napus germplasm via genomic and marker-assisted selection. [ABSTRACT FROM AUTHOR]

Aluminium ([Al.sup.3+]) toxicity restricts productivity and profitability of wheat (Triticum aestivum L.) crops grown on acid soils worldwide. Continued gains will be obtained by identifying superior alleles and novel [Al.sup.3+] resistance loci that can be incorporated into breeding programs. We used association mapping to identify genomic regions associated with [Al.sup.3+] resistance using 1055 accessions of common wheat from different geographic regions of the world and 178 polymorphic diversity arrays technology (DArT) markers. Bayesian analyses based on genetic distance matrices classified these accessions into 12 subgroups. Genome-wide association analyses detected markers that were significantly associated with [Al.sup.3+] resistance on chromosomes 1A, 1B, 2A, 2B, 2D, 3A, 3B, 4A, 4B, 4D, 5B, 6A, 6B, 7A, and 7B. Some of these genomic regions correspond to previously identified loci for [Al.sup.3+] resistance, whereas others appear to be novel. Among the markers targeting TaALMTl (the major [Al.sup.3+]-resistance gene located on chromosome 4D), those that detected alleles in the promoter explained most of the phenotypic variance for [Al.sup.3+] resistance, which is consistent with this region controlling the level of TaALMTl expression. These results demonstrate that genome-wide association mapping cannot only confirm known [Al.sup.3+]-resistance loci, such as those on chromsomes 4D and 4B, but they also highlight the utility of this technique in identifying novel resistance loci. Key words: genetic diversity, wheat, germplasm, DArT, genetic structure, linkage disequilibrium, association mapping. La toxicite de l'aluminium ([Al.sup.3+]) limite la productivite et la profitabilite du blee (Triticum aestivum L.) cultive sur sols acides partout dans le monde. Des gains continus ont ete realises en identifiant des alleles superieurs et de nouveaux locus de resistance a la toxicite; de l'[Al.sup.3+], lesquels sont ensuite incorpores dans des programmes d'ameelioration genetique. Les auteurs ont employee l'analyse d'association pour identifier de nouvelles regions genomiques associeees a la resistance a l'[Al.sup.3+] chez une collection de 1055 accessions du ble tendre provenant de diverses regions du monde et 178 marqueurs DArT polymorphes. Des analyses Bayesiennes fondeees sur les matrices de distance geneetique ont permis de classer ces accessions en 12 sous-groupes. Un balayage genomique a detecte des marqueurs significativement associesa la resistance a l'[Al.sup.3+] sur les chromosomes 1A, 1B, 2A, 2B, 2D, 3A, 3B, 4A, 4B, 4D, 5B, 6A, 6B, 7A et 7B. Certaines de ces regions correspondaient a des locus identifies anteerieurement pour la resistance a l'[Al.sup.3+] tandis que d'autres etaient rapporteees pour la premiere fois. Parmi les marqueurs ciblant TaALMT1, le principal locus de resistance a l'[Al.sup.3+] situe sur 4D, ceux situes au sein du promoteur expliquaient la plus grande part de la variance phenotypique pour la resistance a l'[Al.sup.3+], ce qui suggere que cette region determine le niveau d'expression de TaALMT1. Ces resultats montrent qu'un balayage genomique peut non seulement confirmer l'existence de locus connus de resistance a l'[Al.sup.3+], comme ceux situes sur 4D et 4B, mais demontre aussi l'utilite de cette approche en vue d'identifier des locus de resistance nouveaux. Mots-cles: diversite geneetique, ble, ressources genetiques, DArT, structure geneetique, deseequilibre de liaison, analyse d'assocation. [Traduit par la Redaction], Introduction Aluminium ([Al.sup.3+]) toxicity continues to restrict the productivity and profitability of wheat (Triticum aestivum L. subsp. aestivum;2n = 6x = 42, AABBDD) grown on acidic soils. Under low pH [...]

Abstract Background Molecular marker technologies are undergoing a transition from largely serial assays measuring DNA fragment sizes to hybridization-based technologies with high multiplexing levels. Diversity Arrays Technology (DArT) is a hybridization-based technology that is increasingly being adopted by barley researchers. There is a need to integrate the information generated by DArT with previous data produced with gel-based marker technologies. The goal of this study was to build a high-density consensus linkage map from the combined datasets of ten populations, most of which were simultaneously typed with DArT and Simple Sequence Repeat (SSR), Restriction Enzyme Fragment Polymorphism (RFLP) and/or Sequence Tagged Site (STS) markers. Results The consensus map, built using a combination of JoinMap 3.0 software and several purpose-built perl scripts, comprised 2,935 loci (2,085 DArT, 850 other loci) and spanned 1,161 cM. It contained a total of 1,629 'bins' (unique loci), with an average inter-bin distance of 0.7 ± 1.0 cM (median = 0.3 cM). More than 98% of the map could be covered with a single DArT assay. The arrangement of loci was very similar to, and almost as optimal as, the arrangement of loci in component maps built for individual populations. The locus order of a synthetic map derived from merging the component maps without considering the segregation data was only slightly inferior. The distribution of loci along chromosomes indicated centromeric suppression of recombination in all chromosomes except 5H. DArT markers appeared to have a moderate tendency toward hypomethylated, gene-rich regions in distal chromosome areas. On the average, 14 ± 9 DArT loci were identified within 5 cM on either side of SSR, RFLP or STS loci previously identified as linked to agricultural traits. Conclusion Our barley consensus map provides a framework for transferring genetic information between different marker systems and for deploying DArT markers in molecular breeding schemes. The study also highlights the need for improved software for building consensus maps from high-density segregation data of multiple populations.