Wild grasses as the reservoirs of infection of rust species for winter soft wheat in the Northern Caucasus

Study of the effect of the combined fungicide Abacus Ultra on the population structure of the wheat leaf rust pathogen

Aim. To study the variability of the intrapopulation structure of the causative agent of wheat leaf rust (Puccinia triticina Erikss.) on the basis of pathogenicity under the influence of the combined fungicide Abacus Ultra, SE.

Material and Methods. The studies were carried out in the greenhouse complex of the Federal Research Center of Biological Plant Protection on the winter wheat variety Krasnodarskaya 99 which is susceptible to leaf rust. The material studied was the combined fungicide Abacus Ultra, SE with application rates of 0.75; 1.0; 1.25; 1.5; 1.75 l/ha. The work was carried out according to generally accepted methods.

Results. The influence of the impact of different rates of application of the fungicide Abacus Ultra, SE on the average virulence of the P. triticina population was established, this indicator varying from 40.0% (control [without treatment]) to 19.5% (fungicide application rate 1.75 l/ha). As a result of the analysis of the phenotypic composition of the population, 5 phenotypes were identified. A decrease in the viability of spores of the fungus P. triticina with an increase in the rate of application of the fungicide was established, this indicator varying from 69.1% (0.75 l/ha) to 29.2% (1.75 l/ha). A decrease in the aggressiveness of the population of the causative agent of leaf rust with an increase in the rate of application of the drug was established. The biological effectiveness of the fungicide Abacus Ultra, SE against the pathogen was 95.3–97.8% at the recommended application rate of 1.0–1.5 l/ha.

Conclusion. The study showed that the population of the leaf rust pathogen treated with the chemical fungicide Abacus Ultra, SE is characterised by a change in structure in terms of aggressiveness and virulence, while the sensitivity remains high due to the combination of the active substances pyraclostrobin and epoxiconazole with a different mechanism of action in the preparation.

Analysis of Host-Specific Differentiation of Puccinia striiformis in the South and North-West of the European Part of Russia

Yellow (stripe) rust, caused by Puccinia striiformis Westend. (Pst), is a major disease of cereals worldwide. We studied Pst virulence phenotypes on Triticum aestivum, Triticum durum, and triticale in three geographically distant regions of the European part of Russia (Dagestan and Krasnodar in North Caucasus, and Northwest) with different climate and environmental conditions. Based on the set of twenty differential lines, a relatively high level of population diversity was determined with 67 different Pst pathotypes identified among 141 isolates. Only seven pathotypes were shared by at least two hosts or occurred in the different regions. No significant differentiation was found between regional Pst collections of pathotypes either from T. aestivum or from T. durum. A set of Pst pathotypes from triticale was subdivided into two groups. One of them was indistinguishable from most durum and common wheat pathotypes, whereas the second group differed greatly from all other pathotypes. All sampled Pst isolates were avirulent on lines with Yr5, Yr10, Yr15, and Yr24 genes. Significant variation in virulence frequency among all Pst collections was observed on lines containing Yr1, Yr3, Yr17, Yr27, and YrSp genes and cvs Strubes Dickkopf, Carstens V, and Nord Desprez. Relationships between Russian regional collections of Pst from wheat did not conform to those for P. triticina.