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Leaf rust, caused by the fungus Puccinia triticina, is one of the most damaging rust diseases of wheat in Russia. Populations of P. triticina were monitored in seven regions of Russia from 2001 to 2018, with a total of 5,191 single urediniospore isolates from bread wheat (Triticum aestivum) being analysed. Populations have changed significantly in all regions since 2012, after 2 years of drought (2010–2011). Regional collections of P. triticina were also significantly different between the two periods 2001–2009 and 2012–2018, with changes along two geographic gradients from West Siberia to the north‐west and south‐west (North Caucasia) of the European part of Russia. All tested isolates were avirulent to resistance gene Lr9 in 2001–2009 but, since 2010, virulence to Lr9 has occurred and annually increased in the Asian part of Russia (Ural and West Siberia) due to deployment of cultivars with the Lr9 gene. Virulence to Lr2a and Lr15 was considerably lower in Dagestan (6%–33%) and all European regions (35%–67%) than in Asian regions (84%–96%). During 2001–2009, virulence on Lr1 was also lower in Dagestan (33%) and the European regions (50%–77%) than in Asia (91%–96%); however, by 2012–2018, nearly all isolates were virulent on Lr1. Remarkable changes were observed in frequencies of P. triticina races defined by their virulence/avirulence to Lr1 and Lr2a genes. We postulate the P. triticina population in Dagestan is specific to that area and pathogen populations in European and Asian parts of Russia are distinct. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine whether genetically distinct groups of Puccinia triticina are present in four regions of the Russian Federation. Collections of P. triticina were obtained from the Central, North Caucasus, Volga and West Siberia regions from 2006 to 2010. Ninety-nine single uredinial isolates were tested for virulence phenotype with 20 Thatcher near-isogenic lines of wheat. Forty-one virulence phenotypes were found in the four regions, with eight in common between the widely separated Central and West Siberia regions. A total of 72 isolates were tested for molecular genotype with 23 simple sequence repeat ( SSR) primer pairs, and 66 isolates were used for further analysis after clone correction for virulence and molecular genotype. Analysis of variation showed no overall differentiation of SSR genotypes or virulence phenotypes based on region of origin. Linkage disequilibria for SSR genotypes were high across the entire population. The regional populations had higher than expected levels of allelic heterozygosity that indicated clonal reproduction. Based on cluster analysis of SSR genotypes there were two groups of P. triticina isolates that were widely distributed across Russia. The two SSR groups also differed significantly for virulence. Puccinia triticina may be dispersed from a common source of inoculum in the European or Caucasus regions of Russia. The Russian P. triticina populations were highly differentiated for SSR genotype from populations in Tajikistan, Kyrgyzstan, Uzbekistan, Armenia, Georgia and Azerbaijan and more similar to populations from southern Kazakhstan and northern Kazakhstan. [ABSTRACT FROM AUTHOR]

The accumulation of H2O2 (oxidative burst) and the progress of pathogen development were studied in compatible and incompatible wheat-brown rust interactions. The accumulation of H2O2 was detected in 98·7% of guard cells with appressoria 8 h post inoculation (hpi). The reaction in both susceptible and resistant plants declined 2–3 days post inoculation (dpi). The second phase of the oxidative burst was observed in the mesophyll and/or epidermis. In susceptible plants it began 4–5 dpi and was detected only in the epidermis. In resistant plants the response was observed in the mesophyll. In moderately resistant plants it was induced 1–3 dpi, and the percentage of infection units reached 80–90% 8 dpi. This corresponded with severe necrotic symptoms. In highly resistant plants, the oxidative burst was short and transient. The percentage of infection units with H2O2 accumulation reached its highest level (60–70%) 2 dpi, and decreased thereafter. Four days later, the low percentage and weak DAB staining indicated very low H2O2 accumulation. The localization and the time-course changes of the oxidative burst correlated with the profiles of the micronecrotic response, haustorium mother cell formation and pathogen development termination. An early and localized induction of oxidative burst followed by its rapid quenching correlated with high resistance and almost no disease symptoms. The possible correlation of the oxidative burst and pathogen development patterns with the level and durability of resistance conferred by Lr genes are discussed. [ABSTRACT FROM AUTHOR]

Experiments were performed in controlled conditions to compare several aggressiveness components of an isolate ofPuccinia triticinaon different wheat (Triticum aestivum) genotypes. Latency period, urediniospore production per lesion and per unit of sporulating surface, lesion size, and nitrogen and carbon content of the spores were measured on four host genotypes. Three of the host cultivars (Soissons, Altria and Isengrain) were susceptible and the fourth (Trémie) was resistant to the isolate used in the experiments, producing a mesothetic infection type. In all the analyses, lesion density was used as a covariable. The latent period was identical on the susceptible host cultivars, and there were no marked differences in the urediniospore production capacity when related to the sporulating surface area. In cv. Isengrain, differences in lesion size relative to the other susceptible cultivars resulted in lower urediniospore production per lesion. Urediniospore production per lesion and lesion size were density dependent and decreased exponentially with increasing lesion density. Urediniospore production per unit of sporulating surface was either independent of lesion density or marginally dependent (decreased linearly with a limited rate). On the resistant cultivar, Trémie, the latent period was longer and of a much greater variance compared with the susceptible cultivars. Urediniospore production per lesion was considerably reduced, but this reduction was fully accounted for by a reduction in lesion size, the urediniospore production capacity of the diseased tissue remaining equivalent to that observed in the susceptible cultivars. In all cultivars the C and N contents of the urediniospores were considered unchanged, even if minor differences were detected. [ABSTRACT FROM AUTHOR]