Utilizing X-ray fluorescence (XRF) method to evaluate the content of metal elements in soil and their effects on the total phenolic and flavonoid contents of some medicinal plants.

Soil factors, especially metal elements in the soil, play a significant role in forming and accumulating secondary metabolites, which determine the medicinal properties of medicinal herbs. In this study, the concentrations of some metal elements (K, Mn, Fe, Cu, Zn, and Cr) in Cam Mountain and Tinh Bien Town, An Giang Province, Vietnam, were determined using the XRF method. We simultaneously determined the total phenolic and flavonoid content of some medicinal herbs collected from the collected soil sample areas, thereby assessing the influence of these elements on the formation of secondary metabolites in medicinal plants. The results showed that K, Mn, and Cr were mainly concentrated in the topsoil and transition layers; Fe and Cu elements tended to concentrate in the transition layer and the subsoil when surveying the soil profile. K, Mn, Cu, and Cr concentrations were more focused in Tinh Bien area, while Fe and Zn had higher concentrations at Cam Mountain. Additionally, results from evaluating the relationship between the content of the elements in the soil and the content of two active compounds also showed the correlation regression model between Zn and flavonoid expression by level 4 at the 5% significance level. Thus, the nonlinear model is suitable for evaluating the relationship between the content of metal elements in the soil and the active compound in medicinal plants.

Population structure of Pyricularia oryzae on rice in Vietnam reveals diversified populations with four pandemic and two endemic clusters.

We characterized the genetic structure of 609 strains of Pyricularia oryzae, the fungal pathogen causing rice blast disease, in three main regions in Vietnam using microsatellites (SSR) markers. From the 447 distinct multilocus genotypes identified, six genetic clusters were defined, all of them showing elevated genetic and genotypic diversities. Four of these clusters were related to rice-attacking lineages already described at the worldwide scale, whereas the two remaining clusters were endemic to Vietnam. Strains were unevenly distributed into the six clusters depending on their groups of rice variety (indica / japonica) or type of varieties (traditional / modern) of origin, but none of the clusters was specifically related to these two factors. The highest diversity of blast population was found in Northern mountainous area, and the lowest in Red River Delta in both terms of genetic diversity and gene diversity. Hierarchical AMOVAs confirmed that all three factors considered (rice variety group, type of variety origin and geography) significantly contributed to the population structure of P. oryzae in Vietnam, with highest contribution from rice variety group. Mating types were unevenly distributed among clusters. Combined with results of female fertility and linkage disequilibirum, we hypothesized that clonal reproduction probably occurred in all clusters, but that sexual reproduction likely took place at least in some restricted areas in the Northern mountainous area for strains belonging to the cluster related to the previously described recombinant lineage (worldwide lineage 1). Our study pictures the genetic diversity, population structure and reproductive mode of the blast fungus in central and north Vietnam, and shows that the observed population structure is explained by several factors, the most important one being the variability of rice variety. All these new information might help for elaborating appropriate strategies to controlling the blast disease.

Genome-wide association mapping of leaf mass traits in a Vietnamese rice landrace panel.

Leaf traits are often strongly correlated with yield, which poses a major challenge in rice breeding. In the present study, using a panel of Vietnamese rice landraces genotyped with 21,623 single-nucleotide polymorphism markers, a genome-wide association study (GWAS) was conducted for several leaf traits during the vegetative stage. Vietnamese landraces are often poorly represented in panels used for GWAS, even though they are adapted to contrasting agrosystems and can contain original, valuable genetic determinants. A panel of 180 rice varieties was grown in pots for four weeks with three replicates under nethouse conditions. Different leaf traits were measured on the second fully expanded leaf of the main tiller, which often plays a major role in determining the photosynthetic capacity of the plant. The leaf fresh weight, turgid weight and dry weight were measured; then, from these measurements, the relative tissue weight and leaf dry matter percentage were computed. The leaf dry matter percentage can be considered a proxy for the photosynthetic efficiency per unit leaf area, which contributes to yield. By a GWAS, thirteen QTLs associated with these leaf traits were identified. Eleven QTLs were identified for fresh weight, eleven for turgid weight, one for dry weight, one for relative tissue weight and one for leaf dry matter percentage. Eleven QTLs presented associations with several traits, suggesting that these traits share common genetic determinants, while one QTL was specific to leaf dry matter percentage and one QTL was specific to relative tissue weight. Interestingly, some of these QTLs colocalize with leaf- or yield-related QTLs previously identified using other material. Several genes within these QTLs with a known function in leaf development or physiology are reviewed.