Ivandic et al. (1998) identified a dominant gene conferring resistance to all known races of Puccinia hordei Otth in two accessions of Hordeum vulgare subsp. spontaneum. The gene was mapped using restriction fragment length polymorphism (RFLP) markers in the short arm of chromosome 2H. Since no other Rph gene controlling complete leaf rust resistance in barley has been reported in this region of chromosome 2HS, the gene symbol Rph16 was proposed for this locus. The suggested symbol for resistance allele is Rph16.ae. Two PCR-based markers MWG874 and MWG2133 were shown to co-segregate with the Rph16 gene in two populations and could provide a basis for marker-assisted selection.

Pickering et al. (1998) reported on the interspecific transfer of a leaf rust resistance gene from H. bulbosum to the two-rowed cultivar Vada. The resistance gene is in a segment of the H. bulbosum genome inserted into chromosome 2HS between molecular markers cMWG682 and BCD175. The segment also confers resistance to powdery mildew and has two molecular markers. The low infection type associated with the Rph gene from H. bulbosum may be useful in barley cultivars such as Vada that have a slow rusting reaction.

Kretschmer et al. (1997) mapped the gene for cyst nematode resistance (Ha2 or Rha2) that is in most Australian cultivars with cyst nematode resistance. The Rha2 locus was located near the center of the long arm of chromosome 2H between the molecular markers AWBA21 and MWG694 in both population examined. The Rha2 locus may be part of a super family of disease resistance gene analogs (RGA) in barley and wheat described by Seah et al. (1998). Their data suggest that the barley genome contains at least six sites at which analogs of this family are found, including the Rpg1 (reaction to Puccinia graminis 1) locus in chromosome 7HS. Spielmeyer et al. (1998) reported further on this RGA family in Triticum species and the Cre3 (cereal cyst nematode resistance) locus in wheat homoeologous chromosome group 2.

Two of twelve sodium azide induced mutants in Harrington barley that dramatically reduce phytic acid content of grain and increase inorganic phosphorus in the seed were mapped by Larson et al. (1998). The lpa1-1 (lpa1.1) and lpa2-1 (lpa2.1) mutants, which are named for orthologous loci in maize, reduced the phytic acid content by about 45 and 70%, respectively. Using linkage data based on the Steptoe x Morex molecular marker map, they placed the lpa1 locus near the STS-PCR markers aMSU21 and ABC252 in chromosome 2HL and the lpa2 locus within a recombination interval of approximately 30 cM in the centromeric region of chromosome 7HL.

Komatsuda et al. (1997) identified additional RAPD markers mapping very close to the six-rowed spike 1 (vrs1) locus, which is the major locus controlling spike type in barley, in chromosome 2HL. Later they (Komatsuda et al. 1998) reported on the conversion of nine molecular markers near the vrs1 locus to sequence-tagged markers. The STSs from two of three RAPD markers were dominant and all six STSs from RFLP markers were co-dominant.

Sturaro et al. (1998) isolated a partial cDNA clone Hvex1 from barley encoding a putative hydroxyproline-rich protein of the extensin family from the coenocytic endosperm and the surrounding sporophytic tissues during the early stages of grain development. Their in situ hybridization and Northern analyses revealed that Hvex1 transcripts are expressed in the nucellus, the nucellar epidermis, and the nucellar projection of developing barley grains. Also, Hvex1 transcripts were detected in the vascular tissue of the pericarp, scutellum of the developing embryo, stigma, and root tips. The Hvex1 transcript was found to be coded by a single gene located near the centromere of chromosome 2.

Kleinhofs et al. (1998) presented a method for subdividing the barley chromosome maps into segments of approximately 10 cM intervals (see p. 57 this volume). The barley genome BIN map was based on the Steptoe x Morex molecular marker map. Fifteen segments or BINs for chromosome 2H were produced choosing 16 molecular markers. Detailed information on the markers placed in each BIN is available as an EXCEL spreadsheet in GRAINGENES Gopher. As more morphological markers, economically important genes, and orthologous loci are placed in the BINs, the barley genome BIN map will become an important tool in planning genetic studies and barley breeding. Loci in the same BIN or in adjacent BINs will be difficult to recombine. For example, the Rph16 locus is in BIN 5 of chromosome 2HS and BIN 6 likely contains a minor maturity that delays heading in many two-rowed cultivars under short-day photoperiod conditions.

References:

Ivandic, V., U. Walther, and A. Graner. 1998. Molecular mapping of a new gene in wild barley conferring complete resistance to leaf rust (Puccinia hordei Otth). Theor. Appl. Genet. 97:1235-1239.

Kleinhofs, A., D. Kudrna, and D. Matthews. 1998. Integrating barley molecular and morphological /physiological marker maps. BGN 28:89-91.

Komatsuda, T., I. Nakamura, F. Takaiwa, and S. Oka. 1998. Development of STS markers closely linked to the vrs1 locus of barley, Hordeum vulgare. Genome 41:680-685.

Komatsuda, T., S. Kawasaki, I. Nakamura, F. Takaiwa, F. Taguchi-Shiobara, and S. Oka. 1997. Identification of random amplified polymorphic DNA (RAPD) markers linked to the v locus in barley, Hordeum vulgare L. Theor. Appl. Genet. 95:637-642.

Kretschmer, J.M., K.J. Chalmers, S. Manning, A. Karakousis, A.R. Barr, A.K.M.R. Islam, S.J. Logue, Y.W. Choe, S.J. Barker, R.M.C. Lance, and P. Langridge. 1997. RFLP mapping of the Ha2 cereal cyst nematode resistance gene in barley. Theor. Appl. Genet. 94:1060-1064.

Larson, S.R., K.A. Young, A. Cook, T.K. Blake, and V. Raboy. 1998. Linkage mapping of two mutations that reduce phytic acid content of barley grain. Theor. Appl. Genet. 97:141-146.

Pickering, R.A., B.J. Steffenson, A.M. Hill, and I. Borovkova. 1998. Association of leaf rust and powdery mildew resistance in a recombinant derived from a Hordeum vulgare x Hordeum bulbosum hybrid. Plant Breed. 117:83-84.

Seah, S., K. Sivasithamparam, A. Karakousis, and E.S. Lagudah. 1998. Cloning and characterization of a family of disease resistance gene analogs from wheat and barley. Theor. Appl. Genet. 97:937-945.

Spielmeyer, W., M. Robertson, N. Collins, D. Leister, P. Schulze-Lefert, S. Seah, O. Moullet, and E.S. Ladudah. 1998. A superfamily of disease resistance gene analogs is located on all homoeologous chromosome groups of wheat (Triticum aestivum). Genome 41:782-788.

Sturaro, M., G. Linnestad, A. Kleinhofs, O.A. Olsen, and D.N.P. Doan. 1998. Characterization of a cDNA encoding a putative extensin from developing barley grains (Hordeum vulgare L.). J. Exp. Botany 49:1935-1944.