Investigating the genetic basis of salt-tolerance in common bean: a genome-wide association study at the early vegetative stage

Salinity poses a significant challenge to global crop productivity, affecting approximately 20% of cultivated and 33% of irrigated farmland, and this issue is on the rise. Negative impact of salinity on plant development and metabolism leads to physiological and morphological alterations mainly due to high ion concentration in tissues and the reduced water and nutrients uptake. Common bean (Phaseolus vulgaris L.), a staple food crop accounting for a substantial portion of consumed grain legumes worldwide, is highly susceptible to salt stress resulting in noticeable reduction in dry matter gain in roots and shoots even at low salt concentrations. In this study we screened a common bean panel of diversity encompassing 192 homozygous genotypes for salt tolerance at seedling stage. Phenotypic data were leveraged to identify genomic regions involved in salt stress tolerance in the species through GWAS. We detected seven significant associations between shoot dry weight and SNP markers. The candidate genes, in linkage with the regions associated to salt tolerance or harbouring the detected SNP, showed strong homology with genes known to be involved in salt tolerance in Arabidopsis. Our findings provide valuable insights onto the genetic control of salt tolerance in common bean and represent a first contribution to address the challenge of salinity-induced yield losses in this species and poses the ground to eventually breed salt tolerant common bean varieties.

Development and Application of a Cleaved Amplified Polymorphic Sequence Marker (Phyto) Linked to the Pc5.1 Locus Conferring Resistance to Phytophthora capsici in Pepper (Capsicum annuum L.)

Phytophthora capsici causes destructive disease in several crop species, including pepper (Capsicum annuum L.). Resistance in this species is physiologically and genetically complex due to many P. capsici virulence phenotypes and different QTLs and R genes among the identified resistance sources. Several primer pairs were designed to follow an SNP (G/A) within the CA_011264 locus linked to the Pc5.1 locus. All primer pairs were designed on DNA sequences derived from CaDMR1, a homoserine kinase (HSK), which is a gene candidate responsible for the major QTL on chromosome P5 for resistance to P. capsici. A panel of 69 pepper genotypes from the Southern Seed germplasm collection was used to screen the primer pairs designed. Of these, two primers (Phyto_for_2 and Phyto_rev_2) surrounding the SNP proved successful in discriminating susceptible and resistant genotypes when combined with a restriction enzyme (BtgI). This new marker (called Phyto) worked as expected in all genotypes tested, proving to be an excellent candidate for marker-assisted selection in breeding programs aimed at introgressing the resistant locus into pure lines.

A method for obtaining flexible broccoli varieties for sustainable agriculture

BACKGROUND

The use of high inputs in agriculture resulted in few varieties (hybrids and pure lines) used in all agricultural systems. Also varieties of vegetables, including broccoli, for organic and low-input agriculture, are almost exclusively hybrids, since there are very few specific breeding programs and varieties for sustainable agriculture systems. A strategy to overcome this issue is the adoption of specific breeding programs for developing heterogeneous varieties (i.e. synthetics, open pollinated varieties, composite cross populations and mixtures). In fact, heterogeneous varieties are able to evolve and adapt to specific agro-climatic conditions. The aim of this study was to develop a method (an Evolutionary Breeding Program, EBP) for obtaining heterogeneous varieties of broccoli and test its efficiency in developing highly diverse varieties, as needed in sustainable agriculture. A synthetic variety originated from a landrace was multiplied in different environments for 3 cycles and morpho-phenological and genetic diversity of the derived populations were assessed.

RESULTS

The presented results are the first and unique indication about the efficiency of a short-time EBP for an allogamous species like broccoli. Few morphological changes were observed among varieties multiplied in different environments with different agro-climatic conditions. This could be probably due to the initial genetic diversity of the landrace from which the populations were selected and also to the great plasticity of the crop. However, SSR data highlighted a genetic differentiation among populations multiplied for two/three years across Europe and in Central Italy, that was not so evident when considering morphological data only.

CONCLUSIONS

Few years of multiplication in different environments resulted in genetically differentiated broccoli populations that nonetheless preserved the original genetic diversity and productivity level and appear to evolve in relationship to different environments: the applied EBP is useful for developing heterogeneous materials for sustainable agriculture.

Soil Selenium (Se) Biofortification Changes the Physiological, Biochemical and Epigenetic Responses to Water Stress in Zea mays L. by Inducing a Higher Drought Tolerance

Requiring water and minerals to grow and to develop its organs, Maize (Zea mays L.) production and distribution is highly rainfall-dependent. Current global climatic changes reveal irregular rainfall patterns and this could represent for maize a stressing condition resulting in yield and productivity loss around the world. It is well known that low water availability leads the plant to adopt a number of metabolic alterations to overcome stress or reduce its effects. In this regard, selenium (Se), a trace element, can help reduce water damage caused by the overproduction of reactive oxygen species (ROS). Here we report the effects of exogenous Se supply on physiological and biochemical processes that may influence yield and quality of maize under drought stress conditions. Plants were grown in soil fertilized by adding 150 mg of Se (sodium selenite). We verified the effects of drought stress and Se treatment. Selenium biofortification proved more beneficial for maize plants when supplied at higher Se concentrations. The increase in proline, K concentrations and nitrogen metabolism in aerial parts of plants grown in Se-rich substrates, seems to prove that Se-biofortification increased plant resistance to water shortage conditions. Moreover, the increase of SeMeSeCys and SeCys2 forms in roots and aerial parts of Se-treated plants suggest resistance strategies to Se similar to those existing in Se-hyperaccumulator species. In addition, epigenetic changes in DNA methylation due to water stress and Se treatment were also investigated using methylation sensitive amplified polymorphism (MSAP). Results suggest that Se may be an activator of particular classes of genes that are involved in tolerance to abiotic stresses. In particular, PSY (phytoene synthase) gene, essential for maintaining leaf carotenoid contents, SDH (sorbitol dehydrogenase), whose activity regulates the level of important osmolytes during drought stress and ADH (alcohol dehydrogenase), whose activity plays a central role in biochemical adaptation to environmental stress. In conclusion, Se-biofortification could help maize plants to cope with drought stress conditions, by inducing a higher drought tolerance.

Iron deficiency in barley plants: phytosiderophore release, iron translocation, and DNA methylation

All living organisms require iron (Fe) to carry out many crucial metabolic pathways. Despite its high concentrations in the geosphere, Fe bio-availability to plant roots can be very scarce. To cope with Fe shortage, plants can activate different strategies. For these reasons, we investigated Fe deficient Hordeum vulgare L. plants by monitoring growth, phytosiderophores (PS) release, iron content, and translocation, and DNA methylation, with respect to Fe sufficient ones. Reductions of plant growth, roots to shoots Fe translocation, and increases in PS release were found. Experiments on DNA methylation highlighted significant differences between fully and hemy-methylated sequences in Fe deficient plants, with respect to Fe sufficient plants. Eleven DNA bands differently methylated were found in starved plants. Of these, five sequences showed significant alignment to barley genes encoding for a glucosyltransferase, a putative acyl carrier protein, a peroxidase, a β-glucosidase and a transcription factor containing a Homeodomin. A resupply experiment was carried out on starved barley re-fed at 13 days after sowing (DAS), and it showed that plants did not recover after Fe addition. In fact, Fe absorption and root to shoot translocation capacities were impaired. In addition, resupplied barley showed DNA methylation/demethylation patterns very similar to that of barley grown in Fe deprivation. This last finding is very encouraging because it indicates as these variations/modifications could be transmitted to progenies.

Permanent genetic resources added to molecular ecology resources database 1 October 2012-30 November 2012

This article documents the addition of 153 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Brassica oleracea, Brycon amazonicus, Dimorphandra wilsonii, Eupallasella percnurus, Helleborus foetidus, Ipomoea purpurea, Phrynops geoffroanus, Prochilodus argenteus, Pyura sp., Sylvia atricapilla, Teratosphaeria suttonii, Trialeurodes vaporariorum and Trypanosoma brucei. These loci were cross-tested on the following species: Dimorphandra coccicinea, Dimorphandra cuprea, Dimorphandra gardneriana, Dimorphandra jorgei, Dimorphandra macrostachya, Dimorphandra mollis, Dimorphandra parviflora and Dimorphandra pennigera.