Proposed gene symbols for resistance to Barley Mild Mosaic Virus (BaMMV) in barley

 

T. Konishi

294 Okada, Mabi-cho Kibi-gun, Okayama 710-1311, Japan

 

Soil infestation with barley yellow mosaic virus (BaYMV) is the most serious barley cultivation problem in East Asia and Europe, and it is gradually dispersing to neighboring regions together with barley mild mosaic virus (BaMMV). Both viruses are soil-borne and transmitted by the root-infecting fungus Polymyxa graminis Led. and are classified in the same genus bymovirus. However, they differ in their biological and serological properties, RNA sequences, and aggressiveness to barley cultivars.

The best way to minimize damage caused by these viruses is to grow the resistant cultivars. Extensive surveys of barley accessions have identified resistant genotypes and genetic analyses have elucidated inheritance patterns. Takahashi et al. (1973) first assigned the gene symbol Ym to a gene conferring resistance to BaYMV, and subsequently resistance genes have been assigned symbols up to ym11 (Bauer et al. 1997). However, some of these genes confer resistance to BaYMV while others control resistance to BaMMV. Genes for resistance to BaYMV are designated as rym1, formerly Ym (Konishi et al. 1997), Ym2 (Takahashi et al. 1973), ym3 (Ukai and Yamashita 1980), rym5 (Konishi et al. 1997), and rym6 (Iida et al. 1999).

A mechanical inoculation technique for BaMMV tests was developed by Friedt (1983) and was used to identify other resistance genes in this series. Since mechanical inoculation procedures for BaMMV are easier and more stable than testing for BaYMV in the infested field, many genetic analyses in Europe, especially in Germany, have been conducted using the mechanical inoculation method. The ym4 gene was first identified as a BaYMV resistance gene by this method (Kaiser and Friedt 1989), but later changed to a BaMMV resistance gene by Kaiser and Friedt (1992). This problem arose because barley cultivars are frequently evaluated in Europe in fields infected with both BaYMV and BaMMV. Utilization of mechanical inoculation has identified several genes conferring resistance to BaMMV, but they were included in the ym series and designated as ym4 followed by ym7, ym8, ym9, ym10 and ym11.

It should be pointed out that resistance to BaYMV is different from resistance to BaMMV. Cultivars with the ym3 gene are resistant to BaYMV and susceptible to BaMMV, the same situation is observed for the ym5 cultivars (Konishi and Kaiser-Alexnat 2000). These results strongly support a distinction between genes for BaMMV resistance and those for BaYMV resistance. The gene symbol mm was previously recommended for BaMMV resistance genes (Götz and Friedt 1993). Based on the scheme of three letter symbols for barley genes (Franckowiak et al. 1997), I propose that genes controlling reaction to BaMMV should be designated as rmm, the abbreviated for reaction to barley mild mosaic virus, to distinguish them from rym genes for reaction to barley yellow mosaic virus.

Since the current symbols for designation of genes for reaction to BaYMV and BaMMV is progressive, a new nomenclature system should be considered and applied before serious confusion occurs among barley researchers. The proposed gene symbol changes for factors controlling reactions of barley to infection with BaMMV are as follows:

 

ym4 in Franka and resistant German cultivars to rmm1,

ym7 in HOR3365 to rmm2,

ym8 in 10247 to rmm3,

ym9 in Bulgarian 347 to rmm4,

ym10 in Hiberna to rmm5, and

ym11 in Russia 57 to rmm6.

 

Since the cultivar Franka possesses a gene for resistance to BaYMV in addition to the rmm1 gene for resistance to BaMMV (Konishi and Furusho 2000), I proposed that the rym4 gene symbol be assigned to the BaYMV resistance gene in Franka. As a result, the series of BaYMV resistance genes will be continuous from rym1 to rym6.

For the recommended nomenclature scheme, the reaction of new genes to either BaYMV or BaMMV should be determined first. When tested using mechanical inoculation with BaMMV, the resistance gene should be designated as a BaMMV resistance gene (rmm). Next, the number of genes governing reaction to BaYMV or BaMMV should be investigated and the resistance gene(s) should be mapped by, for example, QTL analysis using molecular markers. The Chinese barley landrace, Mokusekko 3, possesses two genes for resistance to BaYMV, rym1 and rym5 in chromosomes 4HL and 3HL, respectively (Konishi et al. 1997). Further investigations show that some other resistant accessions also contain two resistance genes for BaYMV. Some questions might remain regarding this new system. If a resistance gene reacts to both viruses simultaneously, there is a question as whether the gene symbol should be rym or rmm. I suggest that the rym symbol have priority over rmm because BaYMV is more serious and wide spread than BaMMV. Although genes conferring resistance to both viruses are possible, none have been identified. Most landraces and cultivars as Franka that are resistance to BaYMV and BaMMV appear to possess different genes for reaction to each virus.

 

References:

Bauer, E., J. Weyen, A. Schiemann, A. Graner, and F. Ordon.  1997.  Molecular mapping of novel resistance genes against barley mild mosaic virus (BaMMV). Theor. Appl. Genet. 95:1263-1269.

Franckowiak, J.D., U. Lundqvist, and T. Konishi.  1997.  New and revised names for barley genes. BGN 26:4-8.

Friedt, W.  1983.  Mechanical transmission of soil-borne Barley Yellow Mosaic Virus. Phytopath. Z. 106:16-22.

Götz, R., and W. Friedt.  1993.  Resistance to the barley yellow mosaic virus complex. Differential genotypic reactions and genetics of BaMMV-resistance of barley (Hordeum vulgare L.). Plant Breed. 111:125-131.

Iida, Y., T. Ban, and T. Konishi.  1999.  Linkage analysis of the rym6 resistance gene to Japanese strain II of barley yellow mosaic virus (BaYMV-II) in barley. BGN 29 (in press).

(http://wheat.pw.usda.gov/ggpages/bgn/29/a29-07.html)

Kaiser, R., and W. Friedt.  1989.  Chromosomal location of resistance to Barley Yellow Mosaic Virus in German winter-barley identified by trisomic analysis. Theor. Appl. Genet. 77:241-245.

Kaiser, R., and W. Friedt.  1992.  Gene for resistance to barley mild mosaic virus in German winter barley located on chromosome 3L. Plant Breed. 108:169-172.

Konishi, T., T. Ban, Y. Iida, and R. Yoshimi. 1997.  Genetic analysis of disease resistance to all strains of BaYMV in a Chinese barley landrace, Mokusekko 3. Theor. Appl. Genet. 94:871‑877.

Konishi, T., and M. Furusho.  2000.  German barley cv. >Franka= possesses two different resistance genes to barley yellow mosaic virus (BaYMV) and barley mild mosaic virus. BGN 30 (submitted).

Konishi, T., and R. Kaiser-Alexnat.  2000.  Reaction of barley accessions to BaYMV and BaMMV in Japan, compared with data in Germany. BGN 30 (submitted).

Takahashi, R., J. Hayashi, T. Inouye, I. Moriya, and C. Hirao.  1973.  Studies on resistance to yellow mosaic disease in barley. I. Tests for varietal reactions and genetic analysis of resistance to the disease. Ber. Ohara Inst. landw. Biol., Okayama Univ. 16:1-17

Ukai, Y., and A. Yamashita.  1980.  Induced mutation for resistance to barley yellow mosaic virus. Japan J. Breed. 30:125-130.