Natural variation for Fe-efficiency is associated with upregulation of Strategy I mechanisms and enhanced citrate and ethylene synthesis in Pisum sativum L.

Iron (Fe)-deficiency is a common abiotic stress in Pisum sativum L. grown in many parts of the world. The aim of the study was to investigate variation in tolerance to Fe deficiency in two pea genotypes, Santi (Fe-efficient) and Parafield (Fe-inefficient). Fe deficiency caused greater declines in chlorophyll score, leaf Fe concentration and root-shoot development in Parafield compared to Santi, suggesting greater Fe-efficiency in Santi. Fe chelate reductase activity and ethylene production were increased in the roots of Santi and to a lesser extent in Parafield under Fe deficiency, while proton extrusion was only occurred in Santi. Moreover, expression of the Fe chelate reductase gene, FRO1, and Fe transporter, RIT1 were upregulated in Fe-deficient roots of Santi. Expression of HA1 (proton extrusion) was also significantly higher in Santi when compared to Parafield grown in Fe-deficient conditions. Furthermore, the application of the ethylene biosynthesis inhibitor, 1-aminoisobutyric acid reduced the Fe chelate reductase activity, supporting a direct role for ethylene in its induction. A significant increase in root citrate was only observed in Santi under Fe deficiency indicating a role for citrate in the Fe-efficiency mechanism. Taken together, our physiological and molecular data indicate that genotypic variation in tolerance to Fe deficiency in Santi and Parafield plants is a result of variation in a number of Strategy I mechanisms and also suggest a direct role for ethylene in Fe reductase activity. The pea cultivar, Santi provides a new source of Fe-efficiency that can be exploited to breed more Fe-efficient peas.

Recent advances in faba bean genetic and genomic tools for crop improvement.

Faba bean (Vicia faba L.), a member of the Fabaceae family, is one of the important food legumes cultivated in cool temperate regions. It holds great importance for human consumption and livestock feed because of its high protein content, dietary fibre, and nutritional value. Major faba bean breeding challenges include its mixed breeding system, unknown wild progenitor, and genome size of ~13 Gb, which is the largest among diploid field crops. The key breeding objectives in faba bean include improved resistance to biotic and abiotic stress and enhanced seed quality traits. Regarding quality traits, major progress on reduction of vicine-convicine and seed coat tannins, the main anti-nutritional factors limiting faba bean seed usage, have been recently achieved through gene discovery. Genomic resources are relatively less advanced compared with other grain legume species, but significant improvements are underway due to a recent increase in research activities. A number of bi-parental populations have been constructed and mapped for targeted traits in the last decade. Faba bean now benefits from saturated synteny-based genetic maps, along with next-generation sequencing and high-throughput genotyping technologies that are paving the way for marker-assisted selection. Developing a reference genome, and ultimately a pan-genome, will provide a foundational resource for molecular breeding. In this review, we cover the recent development and deployment of genomic tools for faba bean breeding.

Multiple genetic loci for zinc uptake and distribution in barley (Hordeum vulgare).

Micronutrient malnutrition, often called 'hidden hunger', affects over two billion people globally. This is particularly problematic in developing countries where widespread zinc (Zn) deficiency exists as a result of a predominantly plant-based diet. Furthermore, supplemental fertilizers are often unavailable or unaffordable in impoverished regions where soil infertility is common. Delivery of more Zn via food grains is theoretically possible through selective breeding strategies, but severe technical difficulties associated with trace element research have limited research on the underlying genetic components of Zn nutrition. Genetic dissection of Zn nutrition involved a pre-existing doubled haploid mapping population of barley (Hordeum vulgare). Association of mineral nutrient accumulation traits with regions of the barley genome was determined in two seasons of growth to maturity, using mapmanager qtx and QGene 4.0. Nine genetic loci segregating in the population associated clearly with measured traits, including five that contributed to grain Zn status. Pooling two-row doubled haploids by selecting the three most favourable alleles increased grain Zn content and concentration by an average of 53 and 75%, respectively. These results will inform breeding efforts for increased Zn density in the major food grain, wheat (Triticum aestivum), by enabling syntenic marker-assisted selection in conventional breeding programmes.

Molecular variation among Chinese and global winter faba bean germplasm.

A sample of winter faba bean germplasm from China was compared with germplasm from outside China, using AFLP analyses. Both sets of germplasm were obtained from the National Genebank of China, Institute of Crop Sciences (ICS), Chinese Academy of Agricultural Sciences, Beijing, China. A sample of 39 winter type accessions from outside of China and 204 Chinese landraces and varieties (201 winter types and 3 spring types) were characterized with 10 AFLP primers. These detected 266 polymorphic bands. The Chinese germplasm was clearly separated from the rest of the world in principal component analysis and clustering analysis, with the spring types from China showing the greatest separation. Yunnan germplasm, both landraces and commercial varieties, showed the greatest separation among the germplasm of Chinese winter faba bean provinces. The landraces/varieties from Anhui, Zhejiang, Sichuan, Jianxi, Guizhou and Fujian provinces clustered in a central group.

Induced novel psbA mutation (Ala251 to Thr) in higher plants confers resistance to PSII inhibitor metribuzin in Lens culinaris.

BACKGROUND: Weed competition is a major limitation to worldwide lentil (Lens culinaris Medik.) production in part due to limited effective safe herbicide options. Metribuzin is a photosystem II inhibiting herbicide that provides broad spectrum weed control, however it causes excessive injury in lentil. Dose response analysis of photosystem II inhibiting herbicides and DNA sequencing of the psbA chloroplast gene occurred to quantify the spectrum and mechanism of herbicide resistance in two ethyl-methanesulfonate (EMS) induced mutant lentils. RESULTS: Compared to susceptible parent PBA Flash, the level of metribuzin resistance was 33-fold for mutant M043 and 10-fold for M009. No improvement in resistance occurred in either mutant to bromoxynil, diuron, bromacil and atrazine herbicides. Nucleotide sequencing of the psbA gene of both mutants identified a substitution at position 751 compared to PBA Flash. The resulting deduced amino acid sequence indicated an Ala251 Thr substitution as being most likely responsible for the high level of metribuzin resistance. CONCLUSIONS: The Ala251 Thr substitution discovered in this study is unique in mutagenized higher plants and the first report of an induced psbA target site mutation in higher plants. This target site metribuzin resistance is likely to have a significant impact on lentil production in Australia and worldwide. © 2019 Society of Chemical Industry.

SNP discovery and high-density genetic mapping in faba bean (Vicia faba L.) permits identification of QTLs for ascochyta blight resistance.

Ascochyta blight, caused by the fungus Ascochyta fabae Speg., is a common and destructive disease of faba bean (Vicia faba L.) on a global basis. Yield losses vary from typical values of 35-40% to 90% under specific environmental conditions. Several sources of resistance have been identified and used in breeding programs. However, introgression of the resistance gene determinants into commercial cultivars as a gene pyramiding approach is reliant on selection of closely linked genetic markers. A total of 14,552 base variants were identified from a faba bean expressed sequence tag (EST) database, and were further quality assessed to obtain a set of 822 high-quality single nucleotide polymorphisms (SNPs). Sub-sets of 336 EST-derived simple sequence repeats (SSRs) and 768 SNPs were further used for high-density genetic mapping of a biparental faba bean mapping population (Icarus×Ascot) that segregates for resistance to ascochyta blight. The linkage map spanned a total length of 1216.8 cM with 12 linkage groups (LGs) and an average marker interval distance of 2.3 cM. Comparison of map structure to the genomes of closely related legume species revealed a high degree of conserved macrosynteny, as well as some rearrangements. Based on glasshouse evaluation of ascochyta blight resistance performed over two years, four genomic regions controlling resistance were identified on Chr-II, Chr-VI and two regions on Chr-I.A. Of these, one (QTL-3) may be identical with quantitative trait loci (QTLs) identified in prior studies, while the others (QTL-1, QTL-2 and QTL-4) may be novel. Markers in close linkage to ascochyta blight resistance genes identified in this study can be further validated and effectively implemented in faba bean breeding programs.