Powdery mildew resistance of barley accessions from Dagestan.

Powdery mildew caused by the parasitic fungus Blumeria graminis (DC.) Golovin ex Speer f. sp. hordei Marchal is one of the most common diseases of barley. Growing resistant varieties can signif icantly minimize harmful effects of the pathogen. The specif icity in the interaction between the fungus and its host plant requires a continuous search for new donors of the resistance trait. The powdery mildew resistance of 264 barley accessions from Dagestan and genetic control of the trait in resistant forms were studied under f ield and laboratory conditions. Forty-seven barley lines carrying previously identif ied powdery mildew resistance genes were also examined. During three years, the experimental material was evaluated under severe infection pressure at the Dagestan Experiment Station of VIR (North Caucasus, Derbent). Juvenile resistance against the Northwest (St. Petersburg, Pushkin) pathogen population was evaluated in a climatic chamber. The genetic control of B. graminis resistance in the selected accessions was studied with the application of hybridological and molecular analyses. The level of genetic diversity of Dagestan barley for effective resistance to powdery mildew is very low. Only two accessions, VIR-23787 and VIR-28212, are resistant against B. graminis at both seedling and adult plant stages. The high-level resistance of breeding line VIR-28212 originating from barley landrace VIR-17554 (Ep-80 Abyssinien) from Ethiopia is controlled by the recessive gene mlo11. Accession VIR-17554 is heterogeneous for the studied trait, with the powdery mildew resistant genotypes belonging to two varieties, dupliatrum (an awnless phenotype) and nigrinudum (an awned phenotype). In accession VIR-23787, a recessive resistance gene distinct from the mlo11 allele was identif ied. This accession is supposed to be protected by a new, effective pathogen resistance gene.

[Inheritance of greenbug resistance in several forms of grain sorghum and sudangrass].

The inheritance of resistance against the Krasnodar population of common greenbug Schizaphis graminum Rond. was analyzed in nine accessions of grain sorghum and sudangrass. The dominant gene of cultivar Capbam (k-455, United States) was effective against some greenbug clones and differed from the Sgr1-Sgr11 resistance genes. The gene was designated as Sgr12. The cultivar Capbam was proposed for use as a differentiator in population genetic studies in S. graminum. The cultivar Sarvasi (k-3852, Hungary) contains not only the dominant Sgr1 gene, but also a recessive gene (most likely Sgr2), which is effective against some greenbug clones. Grain sorghum accessions k-928 and k-929 (Gugara Belaya, western China) each carry two highly effective dominant resistance genes, which differ from Sgr1-Sgr4, Sgr6, Sgr9, and Sgr10. In addition, the resistance genes of accession k-929 differ from the Sgr5 gene. Accession k-928 proved to contain an additional dominant resistance gene, which is expressed in response to some greenbug clones. The gene was designated as Sgr13. Sudangrass accessions k-100 and k-122 (Ukraine) each carry two dominant resistance genes. Accessions k-62, k-99 (Ukraine), and k-96 (Russia) each carry one dominant and one recessive resistance gene. The dominant resistance genes that are expressed in the cultivar Odesskaya 25 (k-122) in response to infestation with some clones from the natural greenbug population were designated as Sgr14 and Sgr15.

[The problem of durable resistance of plants to different pests]. / Problema dlitel'no sokhraniaiushcheisia ustoichivosti rastenii k vrednym organizmam.

Different hypotheses concerning durable plant resistance against different pest were tested: 1) resistance is weak and polygenetically controlled; 2) resistance depends on "residual effect" of oligogenes that were overcome by pests. Contrast pair of plants and pests were used in experiments: wheat, barley--facultative parasite Bipolaris sorokiniana Shoem., wheat--obligate parasite Puccinia recondita Rob. ex Desm., sorghum--greenbug Schizaphis graminum Rond. Differential interaction between parasite and host plant resulted in their increased compatibility under long reproduction of parasite on resistant varieties were regarded as criteria of quick overcoming of resistance. The results did not support any hypothesis. The rate of adaptation of B. sorokiniana to the resistant varieties of wheat and barley did not depend on the level of resistance expression (weak, moderate or strong) and genetic control (oligogenic, polygenic or cytoplasmatic). It was shown by hybridological analysis that "residual effect" of oligogenes of sorghum resistance against greenbug depended on small resistance genes, that can be independent or weakly connected with marker oligogene. These data allows to doubt in phenomenon of "residual effect" of oligogenes. It was shown that non specific pathogenicity of parasitic fungi increased during their reproductions on sensitive varieties of plants. Thus, cultivation of sensitive varieties causes damage of crop culture non only because of their own losses, but also by increasing the infection of moderately resistant varieties.

[Inheritance of a sign of a weekly expressed greenbug resistance in sorghum]. / Nasledovanie priznaka slabo vyrazhennoi ustoichivosti sorgo k obyknovennoi zlakovoi tle.

Combined inheritance of oligogenes (Sgr1, Sgr4, Sgr5, and Sgr6) and a weakly expressed resistance to infestation with virulent greenbug clones was studied in sorghum. Under these conditions, the resistance was shown to depend on the interaction between minor resistance genes of the host plant and the virulence genes of the pest rather than on the "residual effect" of oligogenes. The minor genes can be independent of or weakly linked to the major resistance gene. They differentially interact with phytophage genotypes and, contrary to Van der Plank's postulates, are not responsible for the long-term (horizontal) resistance. The possibility of rapidly overcoming the effect of minor genes was confirmed by observation of seasonal dynamics of a natural aphid population on a resistant variety.

[Identification of Sorghum genes responsible for resistance to Green bug]. / Identifikatsiia genov ustoichivosti sorgo k obyknovennoi Zlakovoi tle.

Genes responsible for resistance to greenbug (Schizaphis graminum Rond.) were identified in sorghum. The dominant (Sgr1) and recessive (Sgr2) genes for resistance were revealed in sample k-457 (PI264453, United States). The samples i-589430 (PI264453, Spain) and k-3852 (Sarvasi, Hungary) carry gene Sgr1. These accessions are assumed to also have gene Sgr2. The samples k-9921 (Shallu, United States) and k-9922 (KS-30, United States) have incompletely dominant resistance gene Sgr3. A symbol Sgr4 was assigned to the dominant gene from sample k-6694 (Deer, United States). The dominant Sgr5 and recessive Sgr6 genes were revealed in the samples k-1362 (Durra Belaya, Syria) and k-1240 (Dzhugara Belaya, China). The cultivar Sorgogradskoe (k-9436, Rostovskaya oblast) has gene Sgr5. The samples k-10092 (Odesskii 360, Ukraine) and k-5091 (Cherhata, Marocco) are assumed to have genes Sgr5 and Sgr6. Sample k-924 (Dzhugara Belaya, China) is protected by the dominant gene Srg7 and recessive gene Sgr8. Sample k-923 (Dzhugara Belaya, China) has at least one of these genes. Two dominant complementary genes for resistance (Sgr9 and Sgr10) were revealed in sample k-930 (Dzhugara Belaya, China). One of two dominant genes of sample k-1237 (Dzhugara Belaya, China) was assigned the symbol Sgr11. Genes Sgr5-Sgr11 responsible for resistance to greenbug are new and were not previously used in breeding.