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Background. One of the most harmful diseases of barley in all areas of its cultivation is scald. The causal agent Rhynchosporium commune Zaffarano, B.A. McDonald & A. Linde (formerly – Rhynchosporium secalis (Oudem.) J.J. Davis) is characterized by a high level of variability, which leads to the emergence of new pathotypes and the loss of resistance of a number of cultivars. Most barley cultivars recommended for cultivation are highly affected by the pathogen. The aim of the study was to find new donors of effective barley resistance genes to R. commune.Materials and methods. Resistance to the fungus was tested in 99 accessions of barley landraces from 18 countries under laboratory and field conditions. The experiments employed isolates and clones of R. commune isolated from plants collected in Leningrad Province. Plant resistance was scored using point scales. Genetic control of fungal resistance was studied in the selected accessions using hybridological analysis.Results and conclusions. We identified 3 accessions of barley landraces, which retained high resistance to the fungus for six years of study in the field under inoculation with different populations of R. commune. Accessions k-31504 (Macedonia), k-31505 (Ethiopia) and k-31503 (India) are protected by R. commune resistance genes, which differ from each other, are not allelic to the previously identified effective Rrs9 gene, and manifest themselves throughout all stages of barley ontogenesis. Each of accessions k-31504 and k-31505 incorporates 2 recessive pathogen resistance genes; k-31503 carries 3 recessive resistance genes.

Scald (Rhynchosporium secalis (Oudem.) J.J. Davis pathogenic agent) is one of the most harmful barley diseases. A high variability of this fungi explains the occurrence of new aggressive pathotypes and, accordingly, loss of cultivar resistance. It was found that many recently selected varieties of barley and previously identified sources of resistance to R. secalis are now susceptible to the pathogen. There is only one gene, Rrs9, that maintains efficiency against pathogen populations in Russia. The aim of this study is to find donors of genes for effective resistance to scald with the ability to easily transfer this trait for hybridization. The inheritance of scald resistance in 33 barley landraces was studied. Analysis of the interaction between the pathogen test clones and the host plant revealed a difference between the alleles determining fungal resistance in 32 barley forms, the previously effective genes Rrs4, rrs6, rrs7, and currently effective Rrs9. It was found that 30 accessions are protected by new unidentified genes for scald resistance. Accessions k-18398 and k-16231 from China are likely to possess allelic genes for scald resistance, while the gene (or genes) of accession k-31075 from Nepal is allelic to the Rrs9 gene. It was demonstrated by hybridological analysis that accessions k-3307, k-15868, k-18989 and k-3481 are protected by effective genes for scald resistance, which differ from each other and which are not allelic to the Rrs4, rrs6, rrs7 or Rrs9 genes. Accessions k-15868 and k-3481 possess two complementary recessive genes for scald resistance, k-18989 has two recessive genes, and k-3307 carries one recessive gene for pathogen resistance. The resistance genes of these forms are manifested during all the stages of plant ontogenesis.