We studied the effects of systemic acquired resistance inducer, benzothiadiazole (BT, benzo-(1,2,3-thiadiazole-7-carbothionic acid S-methyl ester, commercial name BION), on the development of brown rust caused by the fungus Puccinia triticina Erikss. in nearly isogenic lines of common wheat (Triticum aestivum L, cv. Thatcher) carrying the resistance genes Lr19 and Lr24. A dependence of BT efficiency on the time between treatment with the inducer and inoculation with urediniospores was observed. A difference in BT action on pathogenesis during wheat line infection with virulent and avirulent P. triticina clones was detected. In compatible combinations, the morphogenesis of virulent clone mycelium was suppressed without the hypersensitive response. The inhibition of the development of avirulent clone colonies was accompanied by the intense hypersensitive response. Treatment with cycloheximide enhanced avirulent clone development during 3 days after inoculation; however, later colony growth ceased.

The role of reactive oxygen species (ROS) in the defense of nearly isogenic lines of common wheat (Triticum aestivum L., cv. Thatcher) with the genes of resistance to brown rust introgressed from Agropyron species was studied using light microscopy. This disease is induced by the fungus Puccinia triticina Erikss. The presence of superoxide anion in the sites of infection was detected with the dye nitro blue tetrazolium. In addition, we studied fungus development on plants treated with the inhibitor of Ca²⁺-channels, verapamil, disturbing penetration into the cells of Ca²⁺ required for ROS generation. During fungus development in the immune line with the Lr38 resistance gene (from A. intermedium (Host) Beuv.), oxidative burst developed at the sites of contacts of appressoria with stomata and exerted a fungicidic effect. When ROS generation was suppressed, the fungus developed haustoria in the mesophyll cells. In plants with the Lr19 gene (from A. elongatum (Host) Beuv.), only moderate amount of superoxide anion accumulated on the cell walls of stomatal guard cells and in the infection structures when the fungus penetrated into the substomatal cavity and in mesophyll cells. In plants with the Lr24 gene (from A. elongatum), superoxide anion was detected only around haustoria. Suppression of ROS generation in plants harboring the Lr19 and Lr24 genes did not affect fungus entrance into the substomatal cavity but facilitated penetration of haustoria into the mesophyll cells. At the same time, in the lines with the Lr1 gene (from T. aestivum), cytological examination did not detect O ₂ ⁻ accumulation in plant cells, whereas treatment with verapamil enhanced mycelium development. In all lines, the suppression of oxidative burst slowed the development of hypersensitive response.

Тенденция преодоления устойчивости к бурой ржавчине интрогрессивных линий мягкой пшеницы с генетическим материалом Aegilops speltoides Tausch

Common wheat cultivars have been protected from stem rust for several decades worldwide by the Sr31 resistance gene transferred from Secale cereale L. (cv. Petkus). In 1998, Sr31 was overcome in Uganda by the Ug99 race of Puccinia graminis f. sp. tritici Eriks. & Henn. (Pgt). The Ug99 race and its derivatives have spread widely in Africa, neighboring regions and Europe. However, Sr31 remains effective in other areas of the world, including Russia. To breed wheat with durable resistance, it is promising to research the resistance mechanisms of nonhost species and introgressive cultivars. The aim of the research was to estimate the resistance of S. cereale and Triticum aestivum cultivars with Sr31 to stem rust and to study the mechanisms of incompatibility of Pgt with plants at the cellular level. The research was carried out in Western Siberia (Russia, Omsk region) in 2018–2022. Rye and wheat with Sr31 (cvs. Kavkaz, Seri 82, Bacanora (=Kauz’s’), NIL Thatcher TcLr26/Sr31) were resistant at the stages of seedling and adult plant, and cv. PWB343 was more susceptible to disease. Cytological studies have shown that Pgt died on the rye plants on the surface, and cv. Petkus intensively suppressed the development of the appressoria necessary to penetrate into tissues. Wheat cultivars inhibited the Pgt development mainly on the surface and while it attempted to penetrate into the stomata (pre-haustorial resistance). It has been demonstrated that Pgt has to adapt step-by-step to the surface and tissue properties for compatible interaction, which may be the reason for the durable effectiveness of Sr31.

The damage to wheat crops by stem rust poses a threat to the food security of the world’s population. The species Thinopyrum ponticum (Podpěra, 1902) (Z.-W. Liu and R.-C. Wang, 1993) is a non-host for the stem rust fungus Puccinia graminis f. sp. tritici Eriks. and Henn. (Pgt). The Sr24, Sr25, and Sr26 genes, transferred from the Th. ponticum to the wheat gene pool, protect cultivars from the disease in different regions of the world. The study of the non-host resistance (NHR) of Th. ponticum and the effects of the introgressed Sr24, Sr25, and Sr26 genes in wheat is important for breeding cultivars with durable resistance to stem rust. The aim of the research is to study the interaction of Pgt with Th. ponticum and common wheat lines with the Sr24, Sr25, and Sr26 genes, in addition to determining the role of ROS in resistance. Wheat lines with Sr24, Sr25, and Sr26 were resistant to the West Siberian Pgt population. Using cytological methods, it was found that the NHR of Th. ponticum and Sr24, Sr25, and Sr26 led to inhibition of the most inoculumdevelopment on the plant surface. This was mainly due to the suppression of the appressoria development and their death at the stage of penetration into the stomata. Upon contact of Pgt appressoria with stomatal guard cells, the generation of the superoxide anion O₂^•− was revealed. This interaction is similar to the stomatal immunity of Arabidopsis thaliana to non-pathogenic bacteria. The results of our studies show that the Sr24, Sr25, and Sr26 genes reproduce the action of some NHR mechanisms in wheat.

The effectiveness of genes for adult plant resistance to leaf rust has been explored in southern West Siberia by the examples of common wheat cv. Thatcher (Tc), which carries the Lr22b gene, and its nearisogenic lines TcLr34 and TcLr37. Lr22b is inefficient; Lr34 slows down the disease development at a mean daily temperature below 16°C, but is poorly efficient at temperatures above 20°C. Lr37 provides high resistance under all conditions. At the heading stage, the TcLr34 and TcLr37 lines show similar components of partial resistance to rust: reduction in the number and sizes of spots and sporogenesis suppression. Cytological examination has revealed partial suppression of the formation of Puccinia triticina infection signs both at the surface and in tissues (appressoria and haustoria) without hypersensitive reaction (HR). Defense mechanisms in the form of an oxidative burst induced by contacts of appressoria with stomata and callose-lignine appositions are discovered. The lignin autofluorescence color differs from fluorescence that is characteristic for HR-accompanied combinations in TcLr34 and TcLr37. The Lr34 and Lr37 genes exert a pleiotropic action on pathogenesis.