GrainGenes

In BGN Vol 22 comprehensive lists were published on 1) Genes for powdery mildew reaction in conjunction with the publication by Jørgensen (1994) and 2) Loci for disease and pest reaction. These lists were updated ultimo 1993 in BGN 23. Since that time the following new data have been published.

In a masters' thesis, Falak (1994) described a powdery mildew resistance gene designated MlTR on barley chromosome 7. It appears likely that it is the effect of this gene that Tinker and Mather (1994) detected as a QTL for severity of powdery mildew attack. In addition they detected the effect of gene Mlg. In a study by Mahadevappa et al. (1994) on the fine-structure of the Mla locus for powdery mildew reaction, genes Mla6, Mla13 and Mla14 were shown to be in distinct and very closely linked loci. In a preliminary report, Schönfeld et al. (1994) described some powdery mildew resistance genes derived from Hordeum spontaneum. They report four new resistance loci and suggest the designations Mlf, Mlj, Mle and mlb. Mlf and Mlj are on barley chromosome 7L (5LI) and mlb is on chromosome 7S (5SI) as indicated by linkage to DNA markers with known positions. The present coordinator consider the symbol mlb invalid because the symbol Mlb has been proposed in 1958 for the gene now known as Mla2 (cf. Jørgensen 1993).

Torp and Jørgensen (1986) and Jørgensen (1988) described three mutagen-induced and second-site suppressor genes that modified the phenotypic expression of the powdery mildew resistance gene Mla12. The three suppressor genes were not linked to gene Mla12. Recently, Freialdenhoven et al. (1994) have shown that two of these genes are allelic in a locus on barley chromosome 2 (2I) that they designate Nar-1 (necessary for Mla12 resistance). Allele symbols were not assigned. The other suppressor locus was designated Nar-2. These two locus symbols have to be considered invalid due to several reasons. First of all, the symbol nar is being used for genes affecting nitrate reductase (Søgaard and Wettstein - Knowles 1987). Secondly, they are not in agreement with the recommended rules for nomenclature and gene symbolization in barley (Anonymous 1992). According to these rules the three alleles should be designated su1a-Ml, su1b-Ml and su2c-Ml in loci su1-Ml (Nar-1) and su2-Ml (Nar-2), respectively. Thirdly, the three suppressor genes affect the phenotypic expression of only some powdery mildew resistance genes, but not that of others, irrespective of whether the resistance genes are in locus Mla or not, as stated by the authors. Therefore, the symbols should contain the code Ml for (powdery mildew), but not a for the Mla locus. In another paper Schulze-Lefert et al. (1994) have described four recessive and allelic mutagen-induced genes that nullify the resistance of powdery mildew resistance genes in locus mlo. The authors propose the designation of this (suppressor) locus as Nor-1 (necessary for Mlo resistance), but no allele designations. This locus symbol also has to be considered invalid because the symbol describe rRNA or DNA genes (or loci or sites) without regard to their capacity to organize a nucleolus (Leitch and Heslop-Harrison 1992). Recently, Pedersen and Linde-Laursen (1994) designated a new rDNA locus as Nor-I6. Some of these loci are common to different Triticeae species and are designated Nor across species (McIntosh 1988). A more appropriate designation for this locus (Nor-1) could be either su3-Ml with four alleles from su3d-Ml to su3g-Ml, or - if the locus is really specific for Mlo resistance - from su1a-mlo to su1d-mlo.

Jin et al. (1994) have described a recessive stem rust resistance gene effective to the new pathotype Pgt-QCC of stem rust that threatens North American barley production. They suggest the locus and allele symbols Rpg4 and rpg4d, respectively.

Chen et al. (1994) used molecular markers and chromosome-doubled haploid lines (DH-lines) to identify and manipulate genes for stripe rust resistance in barley. They report one stripe rust resistance "gene" on each of the M (minus) arms of chromosomes 7(5I) and 4(4I). The one on chromosome 7 has a major effect whereas that on chromosome 4 has a minor effect. Gene or locus designations were not proposed.

A similar approach was used by Barua et al. (1993) in a study on the genetic basis of some morphological traits and reaction to scald (Rhynchosporium secalis). A scald reaction QTL was mapped close to two RAPD markers on chromosome 3L(3IL). No locus designation was proposed.

References:

Anonymous, 1992. Recommended rules for nomenclature and gene symbolization. BGN 21: 11-15.

Barua, U.M., Chalmers, K.J., Thomas, W.T.B., Hackett, C.A., Lea, V., Jack, P., Forster, B.P., Waugh, R. and Powell, W. 1993. Molecular mapping of genes determining hight, time to heading, and growth habit in barley (Hordeum vulgare). Genome 36: 1080-1087.

Chen, F.Q., Prehn, D., Hayes, P.M., Mulrooney, D., Corey, A. and Vivar, H.1994. Mapping genes for resistance to barley stripe rust. Theor. Appl. Genet. 88: 215-219.

Falak, I. 1994. Analysis of a doubled haploid barley population for resistance to powdery mildew. M. Sc. Thesis, Department of Crop Science, University of Guelph, Ontario, Canada, pp. 168.

Freialdenhoven, A., Scherag, B., Hollricher, K., Collinge, D.B., Thordal-Christensen, H. and Schulze-Lefert, P. 1994. Nar-1 and Nar-2, two loci required for Mla12 -specified race-specific resistance to powdery mildew in barley. The Plant Cell 6: 983-994.

Jin, Y., Steffenson, B.J. and Miller, J.D. 1994. Inheritance of resistance to pathotypes QCC and MCC of Puccinia graminis f.sp. tritici in barley line Q 21861 and temperature effects on the expression of resistance.Phytopath. 84: 452-455.

Jørgensen, J.H. 1988. Genetic analysis of barley mutants with modifications of powdery mildew resistance gene Ml-a12. Genome 30: 129-132.

Jørgensen, J.H. 1993. Coordinator's report: Disease and pest resistance genes. BGN 22: 110-134.

Jørgensen, J.H. 1994. Genetics of powdery mildew resistance in barley. Crit. Rev. Plant Sci. 13: 97-119.

Leitch, I.J. and Heslop-Harrison, J.S. 1992. Physical mapping of the 18S-5.8.S-26S rDNA genes in barley by in situ hybridization. Genome 35: 1013-1018.

Mahadevappa, M., DeScenzo, R.A. and Wise, R.P. 1994. Recombination of alleles conferring specific resistance to powdery mildew at the Mla locus in barley. Genome 37: 460-468.

Pedersen, C. and Linde-Laursen, I. 1994. Chromosomal locations of four minor rDNA loci and a marker satellite sequence in barley. Chrom. Res. 2: 65-71.

Schönfeld, M., Fischbeck G. und Jahoor A. 1994. Identifizierung und Lokalisierung der Mehltauresistenzgene aus der Wildgerste und deren möglicher Einsatz in der Resistenzzüchtung. Vorträge für Pflanzenzüchtung 28: 184-186.

Schulze-Lefert, P., Freialdenhoven, A., Scherag, B. and Görg, R. 1994. Dissection of resistance pathways in barley to powdery mildew attack. M.J. Daniels et al. (eds.), Advances in Molecular Genetics of Plant-Microbe Interactions 3, Kluwer Academic Publishers: 309-312.

Søgaard, B. and Wettstein - Knowles, P. von 1987. Barley: Genes and chromosomes. Carlsberg Res. Comm. 52: 123-196.

Tinker, N.A. and Mather, D.E. 1994. Main effects of quantitative trait loci in Harrington/TR306 two-row barley. BGN 23: 72-78.

Torp, J. and Jørgensen, J.H. 1986. Modification of barley powdery mildew resistance gene Ml-a12 by induced mutation. Can. J. Genet. Cytol. 28: 725-731.