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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.

In conditions of vegetative trial carried out against selective backgrounds in 2017-2019 the response of 27 flax samples to a decrease in soil acidity to neutral pHKCl was studied. The scheme of the experiment was as follows: variant I (control) − pHKCl 5.3-5.5, P2O5 − 320-340 mg/kg, K2O − 81-92 mg/kg; variant II − pHKCl 6.2, P2O5 − 312-345 mg/kg, K2O − 84-98 mg/kg. It has been shown that during the «herringbone» phase in the majority of studied flax genotypes against the background of pH 6.2, the symptoms of “physiological oppression” of flax were observed: small spots developed on the upper leaves, the plants stopped growing, the stems thickened, and the tops of severely affected plants died off. As a result, at the beginning of the growing season at plant height of 7-10 cm, most of the samples were severely affected (from 69 to 100 %). The exceptions were varieties of fibre-flax Hermes (France), Vega 2 (Lithuania), Atlant (Russia) and linseed genotypes No. 3896 (Russia) and Norlin (Canada), which had a weak and medium degree of affection (8.3-45.5 %). Moreover, these genotypes showed a high level of both biological (75-90 %) and agronomic (77.3-85.6 %) resistance in the phase of "early yellow ripeness". The identified flax collection samples can be used as sources of resistance to flax «physiological oppression» caused by stressful edaphic factors in a neutral environment. On the basis of the analysis of the main elements of fiber productivity in studied flax genotypes, it has been established that against the background of pH 6.2 the reduce in plant height was from 11.4 to 52.1 % relative to the control, weight of the technical part of the stem − from 7.2 to 83.4 % , fiber mass − from 9.6 to 85.1 %. For the first time, on the basis of hybridological analysis, an assumption was done as to the pres-ence of a strong dominant gene, controlling the resistance to high soil pH values in the Hermes (France) flax variety and the linseed line No. 3896 (Russia).

Background. Scald (caused by Rhynchosporium secalis (Oudem.) J.J. Davis) is one of the most harmful barley diseases. The pathogen is characterized by the differential interaction with the host plant genotypes. Therefore, the most rational plant breeding strategy should envisage broadening of genetic diversity of cultivated varieties. It has been found that the majority of the recently released barley varieties and of the previously identified sources of resistance to R. secalis are now susceptible to the pathogen. Only the resistance gene Rrs9 maintains efficiency against the pathogen populations in the Russian Northwest. Earlier, we have found scald resistant barleys to be frequent among barley landrace accessions. It was demonstrated by the hybridological analysis that accessions k-3307, k-15868, k-18989 and k-3481 are protected by effective scald resistance genes that differ from each other, and which are not allelic to the Rrs4, rrs6, rrs7 or Rrs9 genes. The goal of the present work was to study genetic control to the dangerous pathogen in four other barley landraces. Materials and methods . The inheritance of scald resistance was analyzed in barley accessions k-16233, k-27205 (China), k-27768 (India) and k-22299 (Ecuador). The study employed two experimental techniques, that is, the pathogen/host plant differential interactions analysis in the lab, and the hybridological analysis in the field. The experiments were carried out using R. secalis isolates and clones from the pathogen populations sampled in the North Caucasus and the Russian Northwest. Resistance was scored against the scales from 0 (no symptoms) to 4 points (in the lab), and from 0 to 5 points (in the field). Plants that scored 0-2 points were regarded as resistant. Results and conclusions . The analysis of the pathogen clone/host plant interaction has shown that the landraces k-16233, k-27205 (China), k-27768 (India) and k-22299 (Ecuador) are protected by effective genes of scald resistance which differ from each other and are non-allelic to the previously effective genes Rrs4, rrs6, rrs7 and the currently effective Rrs9. According to the hybridological analysis data, k-27205 has one dominant gene of scald resistance; k-16233, k-27768 and k-22299 are protected by two dominant effective resistance genes, all of which manifest themselves at all the stages of plant ontogenesis.

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.

Variation in stomatal guard cell length of parental cultivars and its inheritance in F1 and F2 hybrids have been studied after crossing between contrast genotypes of winter wheat (Triticum aestivum L.). Analysis of F2 populations has shown the action of three non-allelic genes in control of stomatal guard cell length of parental cultivars