Highly Aggressive Invasive Race Group PstS2 in Russian Populations of the Wheat Yellow Rust Pathogen.

The expansion of the area of harmfulness of the wheat yellow rust pathogen (Puccinia striiformis) (Pst) has be observed all over the world in the 2000s. This is due to the emergence of new highly aggressive invasive groups of races PstS1 and PstS2, adopted to the high temperatures, and also as a result of virulence mutations of regional pathogen populations. SCAR-markers were developed for identification of invasive races, and pathogen collections from many countries were studied. In these studies in first in Russia, the analysis of regional populations of P. striiformis for the presence of invasive races PstS1 and PstS2 was carried out. Single pustule isolates were obtained from urediosamples collected from common and durum wheat, triticale and wild grasses in seven regions of the Russian Federation (North Caucasian, Northwestern, Central Black Earth, Lower Volga, Middle Volga, Volga-Vyatka, West Siberian) in 2019-2020. In total 82 isolates were studied. Using SCAR markers, three genotypes were identified in the studied collection of P. striiformis, and one of which belongs to the invasive group PstS2. The other two genotypes had a different origin (other). Isolates of PstS2 group were received from pathogen population samples collected in the Russian Northwest in 2020. Virulence analysis revealed two phenotypes among them: PstS2_R1 (3 isolates) and PstS2_R2 (1 isolate). According to information from the Global Rust Reference Center ( http://www.wheatrust.org/ ), the main characteristic of isolates from invasive PstS2 group is virulence to wheat lines with resistance genes Yr2, Yr6, Yr7, Yr8, Yr9, and Yr25. The Russian R1 phenotype PstS2 was also characterized by virulence to these genes, as well as to Yr1, Yr32, and YrSp. The PstS2_R2 phenotype differed from PstS2_R1 for avirulence to Yr25 and virulence to Yr3 and Yr4. The main difference of Russian PstS2 isolates with detected in other countries is virulence to wheat lines with genes Yr4, Yr32, and YrSp. The first detection of invasive races in the Northwest of Russia indicates the relevance of annual monitoring of regional populations of P. striiformis.

The effect of the 7DL-7Ae#1L·7Ae#1S translocation on the productivity and quality of spring bread wheat grain.

The 7DL-7Ae#1L·7Ae#1S translocation with the Lr29 gene attracts the attention of bread wheat breeders by its effectiveness against Puccinia triticina. However, its impact on useful agronomic traits has been little studied. In this report, the prebreeding value of 7DL-7Ae#1L·7Ae#1S was studied in analogue lines (ALs) of spring bread wheat cultivars Saratovskaya 68 and Saratovskaya 70 during 2019-2021. The presence of the Lr29 gene was conf irmed by using molecular marker Lr29F24. The ALs with the Lr29 gene were highly resistant to P. triticina against a natural epiphytotics background and in laboratory conditions. 7DL-7Ae#1L·7Ae#1S in Saratovskaya 68 ALs reduced grain productivity in all years of research. On average, the decrease was 35 and 42 %, or in absolute f igures 1163 and 1039 against 1802 kg/ha in the cultivar-recipient. In Saratovskaya 70 ALs, there was a decrease in grain yield in 2019 and 2020, and there were no differences in 2021. On average, the decrease was 18 and 32 %, or in absolute f igures 1101 and 912 against 1342 kg/ha in the cultivar-recipient. The analogues of both cultivars showed a signif icant decrease in the weight of 1000 grains, which ranged from 14 to 20 % for Saratovskaya 68 and 17-18 % for Saratovskaya 70. An increase in the period of germination-earing was noted only in Saratovskaya 68 lines, which averaged 1.3 days. ALs of Saratovskaya 70 had no differences in this trait. 7DL-7Ae#1L·7Ae#1S did not affect plant height and lodging resistance in all ALs. Studies of the bread-making quality in lines with 7DL-7Ae#1L·7Ae#1S revealed a signif icant increase in grain protein and gluten content. As for the effect on the alveograph indicators, there were differences between ALs of both cultivars. While Saratovskaya 68 ALs had a decrease in elasticity and in the ratio of dough tenacity to the extensibility, Saratovskaya 70 lines had an increase in these indicators. All lines increased the f lour strength and the loaves volume, but while Saratovskaya 68 ALs had an increased porosity rating, Saratovskaya 70 ALs had the same rating as the recipient.

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

Common winter wheat is the main grain crop cultivated in the North Caucasus. Rust disease damage is one of the factors limiting wheat productivity. There are three species of rust in the region: leaf (Puccinia triticina), stem (P. graminis) and stripe rust (P. striiformis), and their signif icance varies from year to year. The most common is leaf rust, but in the last decade the frequency of its epiphytotic development has signif icantly decreased. At the same time, an increase in the harmfulness of stripe rust (P. striiformis) is noted. Stem rust in the region is mainly absent or observed at the end of the wheat growing season to a weak degree. Only in some years with favorable weather conditions its mass development is noted on susceptible cultivars. It is believed that the sources of infection with rust species in the North Caucasus are infested soft wheat crops, wild-growing cereals and exodemic infection carried by air currents from adjacent territories. In the North Caucasus, forage and wild grasses are affected by Puccinia species almost every year. Depending on weather conditions, the symptom expression is noted from late September to December and then from late February to May-June. Potentially, an autumn infection on grasses can serve as a source for infection of winter soft wheat cultivars sown in October. The purpose of these studies is to characterize the virulence of P. triticina, P. graminis, P. striiformis on wild cereals and to assess the specialization of causative agents to winter wheat in the North Caucasus. Infectious material represented by leaves with urediniopustules of leaf, stem and stripe rusts was collected from wild cereals (Poa spp., Bromus spp.) in the Krasnodar Territory in October-November 2019. Uredinium material from P. triticina, P. striiformis, and P. graminis was propagated and cloned. Monopustular Puccinia spp. isolates were used for virulence genetics analysis. In experiments to study the specialization of rust species from wild-growing cereals on common wheat, 12 winter cultivars were used (Grom, Tanya, Yuka, Tabor, Bezostaya 100, Yubileynaya 100, Vekha, Vassa, Alekseich, Stan, Gurt, Bagrat). These cultivars are widely cultivated in the North Caucasus region and are characterized by varying degrees of resistance to rust. Additionally, wheat material was inoculated with Krasnodar populations of P. triticina, P. striiformis, P. graminis from common wheat. In the virulence analysis of P. triticina on cereal grasses, four phenotypes (races) were identif ied: MCTKH (30 %), TCTTR (30 %), TNTTR (25 %), MHTKH (15 %), and f ive were identif ied in P. graminis (RKMTF (60 %), TKTTF, RKLTF, QKLTF, LHLPF (10 % each). Among P. striiformis isolates, three phenotypes were identif ied using the International and European sets of differentiating cultivars - 111E231 (88 %), 111E247 (6 %) and 78E199 (6 %). Using isogenic Avocet lines, 3 races were also identif ied, which differed among themselves in virulence to the Yr1, Yr11, Yr18 genes (with the prevalence of virulent ones (94 %)). Composite urediniums' samples (a mixture of all identif ied races) of grass rust of each species were used to inoculate winter wheat cultivars. The most common winter wheat cultivars (75 %) were characterized by a resistant response when infected with P. graminis populations from common wheat and cereal grasses. All these cultivars were developed using donors of the rye translocation 1BL.1RS, in which the Lr26, Sr31, and Yr9 genes are localized. The number of winter wheat cultivars resistant to leaf rust in the seedling phase was lower (58 %). At the same time, all the studied cultivars in the seedling phase were susceptible to P. striiformis to varying degrees. The virulence analysis of the leaf, stem and stripe rust populations did not reveal signif icant differences in the virulence of the pathogens between wild-growing cereals and soft wheat. Urediniomaterial of all studied rust species successfully infested soft wheat cultivars. The results obtained indicate that grasses are rust infection reservoirs for common wheat crops in the North Caucasus.