Sequences of cloned resistance genes from a wide range of plant taxa reveal significant similarities in sequence homology and structural motifs. This is observed among genes conferring resistance to viral, bacterial, and fungal pathogens. In this study, oligonucleotide primers designed for conserved sequences from coding regions of disease resistance genes N (tobacco), RPS2 (Arabidopsis) and L6 (flax) were used to amplify related sequences from soybean [Glycine max (L.) Merr.]. Sequencing of amplification products indicated that at least nine classes of resistance gene analogs (RGAs) were detected. Genetic mapping of members of these classes located them to eight different linkage groups. Several RGA loci mapped near known resistance genes. A bacterial artificial chromosome library of soybean DNA was screened using primers and probes specific for eight RGA classes and clones were identified containing sequences unique to seven classes. Individual bacterial artificial chromosomes contained 2-10 members of single RGA classes. Clustering and sequence similarity of members of RGA classes suggests a common process in their evolution. Our data indicate that it may be possible to use sequence homologies from conserved motifs of cloned resistance genes to identify candidate resistance loci from widely diverse plant taxa.

A map of the barley genome consisting of 295 loci was constructed. These loci include 152 cDNA restriction fragment length polymorphism (RFLP), 114 genomic DNA RFLP, 14 random amplified polymorphic DNA (RAPD), five isozyme, two morphological, one disease resistance and seven specific amplicon polymorphism (SAP) markers. The RFLP-identified loci include 63 that were detected using cloned known function genes as probes. The map covers 1,250 centiMorgans (cM) with a 4.2 cM average distance between markers. The genetic lengths of the chromosomes range from 124 to 223 cM and are in approximate agreement with their physical lengths. The centromeres were localized to within a few markers on all of the barley chromosomes except chromosome 5. Telomeric regions were mapped for the short (plus) arms of chromosomes 1, 2 and 3 and the long (minus) arm of chromosomes 7.

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Grain protein concentration is an important determinant of grain quality in many crops, including wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). While high grain protein percentage might be desirable in barley destined for monogastric feed, low grain protein concentration is desirable for malt and beer production. Low grain protein concentration is associated with increased levels of malt extract and reduced problems with beer chill haze. Molecular markers were used to map and characterize the genes responsible for low, stable grain protein concentration in a recombinant inbred line population developed from a cross between ‘Karl’ (CIho 15487), a low grain protein six‐rowed barley, and ‘Lewis’ (CIho 15856), a standard two‐rowed cultivar. Three major quantitative trait loci (QTL) were identified which impacted grain protein percentage. Two of these grain protein effects appeared to result from gene action impacting flowering date. This pleiotropic relationship may be the main reason agronomically acceptable, low protein cultivars have yet to be released.

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