Switchgrass (Panicum virgatum L.), is a warm season C 4 perennial grass, native to North American tall grass prairies. The high biomass production potential of switchgrass with low inputs makes it an excellent choice as a sustainable bioenergy crop. The objective of this study was to determine the genetic variability within and among 31 switchgrass populations obtained from Germplasm Resources Information Network (GRIN). Six plants from each population (186 genotypes) were characterized with 24 conserved grass expressed sequence tag-simple sequence repeats (EST-SSR) and 39 switchgrass EST-SSR markers. The partitioning of variance components based on the analysis of molecular variance (AMOVA) revealed that the variability within population was significantly higher (80%) than among populations (20%). Pair-wise genetic distance estimates based on SSR data revealed dissimilarity coefficients for genotypes ranging from 0.45 to 0.81. The uplands and lowlands were generally grouped in distinct sub-clusters. The genotypes were grouped into the different adaptive zones based on the geographical locations of the collections. Ploidy estimation showed that 20 of the accessions were tetraploid, four of them were octoploids and the remaining seven had mixed ploidy levels. Flow cytometry analysis of genotypes within cultivars collected from commercial seed sources did not always support the ploidy mixtures that were found in GRIN collections. Three genotypes of two accessions that clustered differently from other genotypes of the same accessions also had different ploidy levels.

Advanced backcross quantitative trait locus (AB-QTL) analysis was used to identify QTLs for yield and yield components in a backcross population developed from a cross between hard red winter wheat (Triticum aestivum L.) variety Karl 92 and the synthetic wheat line TA 4152-4. Phenotypic data were collected for agronomic traits including heading date, plant height, kernels per spike, kernel weight, tiller number, biomass, harvest index, test weight, grain yield, protein content, and kernel hardness on 190 BC2F(2:4) lines grown in three replications in two Kansas environments. Severity of wheat soil-borne mosaic virus (WSBMV) reaction was evaluated at one location. The population was genotyped using 151 microsatellite markers. Of the ten putative QTLs identified, seven were located on homologous group 2 and group 3 chromosomes. The favorable allele was contributed by cultivated parent Karl 92 at seven QTLs including a major one for WSBMV resistance, and by the synthetic parent at three QTLs: for grain hardness, kernels per spike, and tiller number.

Aluminum (Al) toxicity in acid soils is a major limitation to the production of alfalfa (Medicago sativa subsp. sativa L.) in the USA. Developing Al-tolerant alfalfa cultivars is one approach to overcome this constraint. Accessions of wild diploid alfalfa (M. sativa subsp. coerulea) have been found to be a source of useful genes for Al tolerance. Previously, two genomic regions associated with Al tolerance were identiWed in this diploid species using restriction fragment length polymorphism (RFLP) markers and single marker analysis. This study was conducted to identify additional Al-tolerance quantitative trait loci (QTLs); to identify simple sequence repeat (SSR) markers that Xank the previously identiWed QTLs; to map candidate genes associated with Al tolerance from other plant species; and to test for co-localization with mapped QTLs. A genetic linkage map was constructed using EST-SSR markers in a population of 130 BC 1 F 1 plants derived from the cross between Al-sensitive and Altolerant genotypes. Three putative QTLs on linkage groups LG I, LG II and LG III, explaining 38, 16 and 27% of the phenotypic variation, respectively, were identiWed. Six candidate gene markers designed from Medicago truncatula ESTs that showed homology to known Al-tolerance genes identiWed in other plant species were placed on the QTL map. A marker designed from a candidate gene involved in malic acid release mapped near a marginally signiWcant QTL (LOD 2.83) on LG I. The SSR markers Xanking these QTLs will be useful for transferring them to cultivated alfalfa via marker-assisted selection and for pyramiding Al tolerance QTLs.

Aluminum toxicity and soil acidity are major constraints in alfalfa (Medicago sativa subsp. sativa) production in the world. Despite intense research efforts, neither an effective screening procedure nor an Al‐tolerant alfalfa germplasm is available. This dictates the need for identifying a new source of Al‐tolerant genes in the closely related species M. truncatula (barrel medic). Our objectives were to compare three Al tolerance screening methods: (i) a seedling‐based hydroponics method, (ii) a soil‐based plant method, and (iii) an Al‐stressed seedling‐based lumogallion root staining method in 32 M. truncatula accessions. The soil system compared the genotypes for dry root and shoot weights in unlimed soil and for relative weights. The lumogallion root staining of Al‐stressed seedlings compared the genotypes for fluorescence intensity of Al‐bound lumogallion within the root tips. In the hydroponics system, the genotypes were compared for root elongation and relative growth. The three methods were different from each other, with altered rankings for genotypes across the methods. The soil assay demonstrated a higher capacity for discriminating Al response among genotypes with a higher reproducibility. Most of the genotypes that were Al‐tolerant in soil were also Al‐tolerant using the hydroponics and root staining methods. The results suggested that a combination of soil‐based and hydroponics screening might be essential to identify Al‐tolerant genotypes possessing multiple Al tolerance mechanisms.

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