Genetic diversity of a global collection of maize genetic resources in relation to their subspecies assignments, geographic origin, and drought tolerance.

The genetic diversity among an international collection of 40 maize accessions has been evaluated using DNA ISSR fingerprinting. Among the 180 ISSR markers scored by 15 primers, 161 markers (89.59%) were polymorphic and 19 were unique in 16 accessions. A cluster tree based on the average distance coefficients and the Dice similarity indices divided the accessions into three major groups, each including clusters of accessions assigned to their subspecies. However, a low level of genetic differentiation among the accessions was demonstrated by the STRUCTURE analysis of ISSR data in agreement with the low gene flow (Nm) value among the accessions. A scatter diagram of the principal component analysis (PCA) based on ISSR data analysis revealed that the accessions were differentiated into three groups comparable to those produced by the cluster analysis, in which some accessions of the same subspecies showed a close similarity to each other. A scatter diagram of the principal coordinate analysis (PCoA) based on the drought tolerance indices (DTIs) showed that nine genetically similar accessions share drought tolerance characteristics; these include four of subsp. indurata, three of subsp. everata, and two of subsp. indentata. An abundance of unique ISSR alleles found in the 16 accessions, including the nine drought-tolerant accessions, represents rich untapped genetic resources and these accessions may be exploited in the future breeding of maize commercial lines.

Genetic diversity and volatile oil components variation in Achillea fragrantissima wild accessions and their regenerated genotypes.

BACKGROUND: Wild medicinal plants are suffering natural environmental stresses and habitat destruction. The genetic diversity evaluation of wild accessions and their in vitro raised genotypes using molecular markers, as well as the estimation of substances of pharmaceutical value in wild plants and their regenerated genotypes are convenient approaches to test the genetic fidelity of regenerated plants as a source of substances of pharmaceutical value. In this study, the genetic diversity of 12 accessions of the medicinal plant Achillea fragrantissima, representing five sites in the mountains of South Sinai, Egypt, were estimated by the inter simple sequence repeats (ISSR) fingerprinting and their volatile oil components were identified using gas chromatography-mass spectrometry (GC-MS) analysis. The same accessions were regenerated in vitro and the genetic diversity and volatile oil components of propagated genotypes were determined and compared to their wild parents. RESULTS: Clustering and principal component analyses indicated that the wild accessions and their regenerated genotypes were genetically differentiated, but the regenerated plants are relatively more diverse compared to their wild parents. However, genetic variation between wild accessions is inherited to their in vitro propagated genotypes indicating genotypic differentiation of the examined accessions. The number of volatile oil compounds in the wild A. fragrantissima accessions was 31 compounds while in the in vitro propagated plants only 24 compounds were detected. Four major compounds are common to both wild and regenerated plants; these are artemisia ketone, alpha-thujone, dodecane, and piperitone. CONCLUSIONS: Genome profiling and essential oil components analysis showed variations in A. fragrantissima accessions from different populations. Genetic differences between wild and regenerated genotypes were analyzed and validated with the final conclusion that in vitro conditions elicited higher genetic variation that is associated with reduced amount and diversity in the essential oil components.

Molecular Phylogeny of Trifolium L. Section Trifolium with Reference to Chromosome Number and Subsections Delimitation.

The genus Trifolium is one of the largest genera of the legume family Fabaceae with ca. 255 species. The genus is divided into eight sections; the section Trifolium is a major section of the genus, comprising 73 species mainly distributed in the Mediterranean region. We used nuclear ribosomal DNA internal transcribed spacer (ITS) and morphological variation to reconsider the delimitation and phylogenetic relationships of species in the section Trifolium with reference to chromosomal variations. Bayesian analysis of ITS data delimited the species as three clades based on the analysis of ITS sequence and informative indels in combination with morphological variation. The phylogeny of the species by different analyses methods does not support their current delimitation in 17 subsections. The basic chromosome number x = 8 is the number for the genus Trifolium, from which x = 7, 6 and 5 were derived through successive aneuploidy events. With reference to the distribution of these numbers in the species of the section Trifolium, species in clade III and clade II are more evolved than species in clade I.

Screening for Drought Tolerance in Maize (Zea mays L.) Germplasm Using Germination and Seedling Traits under Simulated Drought Conditions.

Maize is known to be susceptible to drought stress, which negatively affects vegetative growth and biomass production, as well as the formation of reproductive organs and yield parameters. In this study, 27 responsive traits of germination (G) and seedlings growth were evaluated for 40 accessions of the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) germplasm collection, under no stress and simulated drought stress treatments by 10%, 15%, and 20% of polyethylene glycol (PEG). The three treatments significantly reduced G% and retarded seedlings growth, particularly the 15% and 20% PEG treatments; these two treatments also resulted in a significant increase of abnormal seedlings (AS). The heritability (H2) and correlations of the traits were estimated, and drought tolerance indices (DTIs) were calculated for traits and accessions. The H2 of G% values were reduced, and H2 for AS% increased as the PEG stress increased. Positive correlations were found between most trait pairs, particularly shoot and root traits, with 48 highly significant correlations under no stress and 25 highly significant correlations under the 10% PEG treatments, particularly for shoot and root traits. The medium to high heritability of shoot and root seedling traits provides a sound basis for further genetic analyses. PCA analysis clearly grouped accessions with high DTIs together and the accessions with low DTIs together, indicating that the DTI indicates the stress tolerance level of maize germplasm. However, the resemblance in DTI values does not clearly reflect the origin or taxonomic assignments to subspecies and varieties of the examined accessions.