Soft wheat is the leading grain crop by value in the world (El-Khoury, 2009). The yield potential of this crop is not fully realized due to the damage to crops by phytopathogens. The diseases significantly reduce the yield and quality of the grain winter wheat. The gross collection losses are up to 20% annually, and in the epiphytotic years – 50% (Novohatka, 1979). Breeding disease-resistant varieties are the most effective method in the struggle against wheat diseases (Palamarchuk et al., 2019).

The creation of resistant varieties largely depends on the correct selection of initial material, determination of genetic factors of resistant control. However, the sources of resistance, the genetic nature sign of resistance to disease, is known identified not enough (Dinh et al., 2020) Therefore, the search and investigation of the immunological features of effective donors of resistance is the main problem in the creation of new competitive winter wheat varieties. Breeders need characteristic the varieties, not only by their phenotypic expression but also by their genetic characteristics recommended for hybridization (Vyerchenko et al., 2019).

The leaf rust, the exciter of which is the fungus Puccinia recondita f. sp. tritici, is one of the most common diseases of wheat in Ukraine and the world. Breeding efficiency for leaf rust resistance can be improved by using different Lr resistance genes. More than 90 Lr genes are registered in the International Catalog Gene Symbol Directory, half of which are alien to date (McIntosh, et al., 2003; McIntosh, et al., 2007; McIntosh, et al., 2008; McIntosh, et al., 2009; McIntosh, et al., 2010; McIntosh, et al., 2011; McIntosh, et al., 2012; McIntosh, et al., 2014; McIntosh, et al., 2016; McIntosh, et al., 2017; McIntosh, et al., 2018; McIntosh, et al., 2019). It is a great interest to investigate the resistance of wild relatives and endemic wheat species, identifying among them new immune forms and new effective resistance genes.

The immunity of Triticum durum and T. dicoccum must be widely used in the breeding of soft wheat for resistance to leaf rust (Leonova et al., 2013). There are no reliable sources of resistance against this pathogen in the culture. But breeders are most interested in resistant varieties found among soft and durum wheat. World collections provide the possibility to use the achievements of breeding in different countries (Kovalyshyna and Dmytrenko, 2017).

The investigation resistance against the disease of the gene pool of wheat is an important task, which can best be a solution from the attitude of the theory of co-evolution of the plant and pathogen (Mushtruk et al., 2020). Only based on such testimony can the right approach be made to the choice of sources of stability and the most effective method of breeding.

The research material was winter wheat the collection specimens received from the World Collection Federal Center for Plant Genetic Resources, All-Russian Institute of Plant Genetic Resources, The Plant Production Institute named after V. Ya. Yuryev of NAAS and varieties of winter wheat from research institutions in Ukraine were materials for investigation.

The investigations were conducted under the conditions of artificial inoculation by the agent of leaf rust in the field infectious nursery of the Mironivka wheat institute named after V.M. Remeslo. A local and synthetic population of the pathogen obtained from the Institute of Plant Protection of the National Academy of Sciences of Ukraine was used for creating an artificial infectious background. The wheat plants contaminated with leaf rust spores in the field in the phase of plant exit into the tube according to the method of (Bober et al., 2020). The variety of Mironivska 10 susceptible to this pathogen is used as an accumulator of infection in experiments. The resistance of plants against the disease was determined on a scale resistance of plants against the disease was determined on a scale (Strahov, 1951), according to which the affection is expressed in relative percentages of leaf area covered with pustules of the pathogen (Geshele, 1971).

Experiments on the evaluation of varieties and collections samples of wheat for disease resistance using artificial inoculation were laid out according to the schemes used in the system of state variety testing of crops (Tkachyk, 2014), using the method developed by us to evaluate the resistance of wheat varieties against pathogens of major diseases (Trybel et al., 2010).

The method of intraspecific hybridization, which was carried out by the "twell method" following the method used for creating the hybrid material of winter wheat (Merezhko et al., 1973).

To identify resistance genes and the nature of the inheritance of the trait of resistance to the agent of leaf rust, using the method of hybridological analysis (Radchenko and Odintsova, 2008). All samples were crossed with tester lines - carriers of known effective resistance genes MС Nair 2203 (Lr9), Flex (Lr19), Osage (Lr24) to identify effective resistance genes. Samples were crossed with each other according to an incomplete diallel scheme to determine the allelic ratio of genes.

The greatest immunological diversity of forms can be detected in the centers of co-origin of the host plant and the pathogen according to the coevolution theory of the host plant and the pathogen (Leary et al., 2018). The center of origin of wheat is located in the Trans-Asian Center, which includes the Caucasus, which plays a leading role in it (Dorofee, 1972). There is also a center for leaf rust formation (Leppik, 1970).

In the work of scientists discovered the pattern in the distribution of immune forms among wheat species for the first time. He considered where there is a species or racial specialization of the pathogen, immune forms and varieties can be found. The Caucasus is the center of origin of many endemic, rust-resistant forms, and should occupy the first place in the globe in terms of the abundance of genetic and physiological types of wheat pointed (Khaneghah et al., 2018). The Triticum timopheevii with complex resistance against all types of rust, powdery mildew, and soot was found in the Caucasus.

10 highly resistant endemic species of wheat and its relatives with the highest immunity to rust, in particular: Triticum monococcum, T. timopheevii, T. militinae, T. Zhykovski, T. fungicidum, Haynatriticum, Aegilops umbellulata are distinguished (Varella et al., 2017).

In the work (Casey et al., 2016) found forms immune to rust, powdery mildew, and soot among Triticum dicoccum.

The principles of researching gene pool of wheat resistance against leaf rust, based on (Flor, 1971) theory of "gene-for-gene", developed (Lodgering, Johnston and Hendricks, 1974; Berlyand-Kozhevnikov et al., 1985).

The majority number of leaf rust resistance genes identified in cultivated wheat varieties are derived from its wild relatives and endemic wheat species. The almost half of the known Lr genes are alien and transferred to Triticum aestivum from different types of wheat, egilops, couch grass, elimus according to the information given in the gene symbol catalogs (McIntosh et al., 2003; McIntosh et al., 2007; McIntosh et al., 2008; McIntosh et al., 2009; McIntosh et al., 2010; McIntosh et al., 2011; McIntosh et al., 2012; McIntosh et al., 2014; McIntosh et al., 2016; McIntosh et al., 2017; McIntosh et al., 2018; McIntosh et al., 2019). The effective sources of resistance genes against the causative agent of leaf rust are aegilops speltoides – genes Lr28, Lr35, Lr36, Lr47, Lr51, Lr66; Aegilops tauschii – Lr4, Lr21, Lr22a, Lr32, Lr39, Lr42; Aegilops umbellulata – Lr9, Lr76; Aegilops triuncialis – Lr58, LrTr; Aegilops ventricosa – Lr37; Aegilops kotschyi – Lr54; Aegilops sharonensis – Lr 56; Aegilops peregrine – Lr59; Aegilops neglecta – Lr62; Aegilops geniculate – Lr57; Elymus trachycaulis – Lr55; Secale cereale – Lr25, Lr26, Lr45; Thinopyrum elongatum – Lr19, Lr29, Lr24; Triticum timopheevii – Lr18, Lr50; Triticum spelta – Lr44, Lr65, Lr71; Triticum dicoccoides – Lr53, Lr64; Triticum timopheevii spp. viticulosum – LrTt1; Triticum turgidum – Lr61;Triticum monococcum – Lr63. All found effective resistance genes except Lr10 and Lr23 are alien.

The new highly efficient resistance genes against the local leaf rust population: LrAc1, LrAc2 – from Aegilops cylindrical, LrTe1, LrTe2 – from Triticum erebuni and LrAd1, LrAd2 – from amphidiploid Ad4 (Triticum dicoccoides x Triticum tauschii) are identified by Babaiants (2011). The collection samples obtained from the National Center for Plant Genetic Resources of Ukraine, varieties of different breeding establishments of Ukraine, and Mironivka Institute of Wheat named after V. M. Remeslo were investigated to select sources of resistance to leaf rust under conditions infectious background of the pathogen on a specially assigned phytoplot.

The effective resistance genes for the Forest Steppe zone of Ukraine leaves: Lr9, Lr19, Lr24, Lr25, Lr37, Lr42 + Lr24, Lr43 (Lr21 + Lr39) + Lr24. It was installed as result investigations of the composition population leaf rust on a series of isogenic lines of Thatcher variety and varieties of carriers of known effective resistance genes (Table 1-2).

There was a slight lesion of Lr19 gene carrier, indicating that clones were virulent against it. In some years, there was a slight lesion of the pathogen and on varieties protected by the Lr9 gene. The varieties protected by the Lr24 gene lose their stability. The Lr37, Lr42 + Lr24, Lr43 (Lr21 + Lr39) + Lr24, Lr9 + Lr26, Lr10 + Lr24, Lr19 + Lr25 genes have shown high efficiency in recent years.

Genes show the high efficiency against the local population of the brown rust pathogen in the Forest-steppe of Ukraine: Lr9, Lr19, Lr37, Lr42 + Lr24, Lr43 (Lr21 + Lr39) + Lr24, Lr9 + Lr26, Lr10 + Lr24 (Kovalyshyna, 2013), Lr24, Lr25, Lr28, Lr34, Lr36, Lr41, Lr42 are determined by results of investigations domestic researchers (Lisova, 2012). The virulence genes against Lr9, Lr19, LrAc1, LrAc2, LrTe1, LrTe2, LrAd1, LrAd2 are rarely found in the Steppe of Ukraine (Babaiants, 2011).

The genetics of the trait resistance of these samples was able to determine by hybrid analysis of F₂ (Table 3). The resistance of variety the Lovrin 32, KM 1485-6-8, VR 89 Bo 22, Beres, Tobarzo, Mironivska 40, Mironivska ostysta, Estet, Mironivskay 28, Volynska napivintensivna, Kyivska 8 is controlled by two dominant genes (15 : 1) (сonfidence probability p = 0.95). The resistance to the agent of leaf rust is controlled by two genes, one of which is dominant and one is recessive (13 : 3) in varieties 0-74-8-2, MIKM 1851-80, 4347-4, NS 326-99, Pliska, 5517 A-5-5 Yr, Florida 302, VR 87 Bo 15, Matyo, HBE 0140-119, HBE 208-120, Expromt, Mironivska 29, Remeslivna, Garant, Selyanka (сonfidence probability p = 0.95). Two complementary genes (9 : 7) control resistance in samples NS 1308, 200-830, Polka, Zernogradskaya 31, Volshebnitsa, Vympel odeskyiy, Erythrospermum 15761 (сonfidence probability p = 0.95). Two duplicate recessive resistance genes (7 : 9) identified in samples NS 2630/1, NS 18-30, Tx 91v4511, Erythrospermum 12557, Erythrospermum 12735 (сonfidence probability p = 0.95). One dominant resistance gene (3 : 1) contains samples HBE 0303 156, HBE 0425-156, and the collection sample Tx 92v4511 contains one recessive resistance gene against leaf rust (1 : 3) (сonfidence probability p = 0.95).

The splitting observed, by crossing sources of resistance among themselves in all combinations of F₂, which confirms the non-identity of genes in these donors. The crossing of resistance donors with testers of known efficient genes Lr9, Lr19, Lr24 observed splitting into resistance and unresistance except for the combination of VR 89 Bo 22 x Flex (Lr19). In ones, splitting into resistance and unresistance phenotypes was not detected. This indicates that VR 89 Bo 22 contains the Lr19 genes (сonfidence probability p = 0.95).

The genetic control of the resistance sign in 42 donors was investigated. The variety VR 89 Bo 22 contains the Lr19 genes. Other donors of this sign have resistance genes independent of the known effective ones, which makes it possible to replenish the leaf rust resistance gene bank and create new heterogeneous winter wheat varieties on this basis.

Successful breeding requires a clear understanding of the evolution of the pathogen and host-pathogen interactions, of the types of resistance, methods of material evaluation, resistance genes, and the nature of inheritance of this trait and its relationship to other economic and biological traits. It is only based on such testimony that the right approach to the choice of sources of resistance and the most effective method of breeding work can be worked out.

The more than 200 collections samples and varieties of winter wheat of different ecological and geographical origins were evaluated for resistance to leaf rust on the artificial infectious background of its pathogen during 1990 – 2018. 42 samples were identified that examined the genetics of resistance to the disease among them. The samples: Lovrin 32, KM 1485-6-8, VR 89 Bo 22, Beres, Tobarzo, 0-74-8-2, MIKM 1851-80, 4347-4, NS 326-99, 5517 A-5-5Yr, Florida 302, VR87Bo15, Matyo, NS 1308, 200-830, Polka, NS 2630/1, NS 18-30, HBE 0140-119, HBE 208-120, HBE 0303 156, HBE 0425-156, Tx91v4511, Tx92v4511, Plyska, Zernogradskaya 31, Volshebnitsa, Myronivska 40, Myronivska ostysta, Myronivska 28, Estet, Volynska napivintensivna, Kyivska 8, Expromt, Myronivska 29, Remrslivna, Garant, Selyaynka, Erythrospermum 15761, Erythrospermum 12557, Erythrospermum 12735, Vympel odeskyiy contain resistance genes are independent of each other and known to be effective (сonfidence probability p = 0.95). In the variety VR 89 Bo 22 one of the genes Lr19. This makes it possible to replenish the leaf rust resistance gene bank and create new heterogeneous varieties of winter wheat.

As a result of studying the composition of the leaf rust population on a series of isogenic lines of Thatcher variety and varieties of carriers of known effective resistance genes, we determined that the resistance genes of the forest-steppe zone of Ukraine remain: Lr9, Lr19, Lr24, Lr25, Lr37, Lr42+Lr24, Lr43 (Lr21 + Lr39) + Lr24.

As a result of research, it was found that the wheat variety Myronivska Ukrainian selection is quite productive in comparison with other varieties and resistant to pathogens of various diseases, especially to the pathogen (brown rust).