Genetic structure of Russian and Kazakhstani leaf rust causative agent Puccinia triticina Erikss. populations as assessed by virulence profiles and SSR markers

Leaf rust caused by Puccinia triticina Erikss is an economically significant disease of spring wheat in the West-Asian Russia and Northern Kazakhstan. Successful wheat breeding for leaf rust resistance necessitates characterization of Lr gene effectiveness, the impact of new wheat varieties on the pathogen virulence, and isolation between populations of P. triticina. Until now, nobody used a uniform infectious material in P. triticina population study, as it was collected from a different set of varieties in each region. Thence, the virulence assessment data were significantly influenced by the 94 effects of host plants. We were the first to compare the structure of P. triticina populations in the West-Asian Russia and Northern Kazakhstan on virulent and molecular genetic properties, using as a source of infectious material a single set of the wheat samples dated 2016 that were tested there within the framework of the Kazakhstan-Siberian Spring Wheat Improvement Network Program (KASIB). Ninety one single-pustule isolates have been tested in the virulence analysis, including 13 isolates from Chelyabinsk, 28 from Omsk, 6 from Kurgan, 16 from Akmolinskaya, 16 from Pavlodarskaya, and 12 from Karagandinskaya provinces. Eleven phenotypes of virulence have been identified with the use of 20 isogenic Thatcher lines with Lr genes (TcLr). The similar phenotypes were found on cultivars Duat, Tertsia, Omskaya 35, Pamyati Azieva, Saratovskaya 29, Chebarkulskaya 3 and line Eritrosperum 85-08. The Russian pathotypes found on variety Astana and lines Lutescens 1003 and Lutescens 6/04-4 differed from Kazakhstan ones in virulence to TcLr11, and those colonizing variety GVK 2074/4 and line Lutescens 715 differed in avirulence to TcLr18. More significant differences in the virulence rang between regional populations have been observed on the line Lutescens 34/08-1 and the variety Rodnik. All studied P. triticina isolates were avirulent to TcLr19, TcLr24 and virulent to TcLr3a, TcLr3bg, TcLr3ka, TcLr14a, TcLr14b, TcLr16, TcLr17, TcLr30. The variation in virulence frequencies was observed on the wheat lines with the genes Lr1, Lr2a, Lr2b, Lr2c, Lr9, Lr15, Lr18, Lr20, and Lr26. Virulence to Lr9 was found in the pathogen populations collected from the wheat samples Duet, Tertsia, Chebarkulskaya 3, Lutescens 34/08-19 carrying this gene. The differences in populations on virulence were found using the indices of genetic distances Nei D and Fst, the analog for binary data in AMOVA. The Nei index values indicated a high similarity between the majority of the Northern-Kazakhstani and Russian populations, except of those from Chelyabinskaya and Karagandinskaya provinces. According to the Fst index, the high similarity was found between the populations from Omsk, Kurgan and Northern Kazakhstan. The Chelyabinsk population appeared to be close to the Kurgan but varied from others. In the test, a total of 46 isolates and 9 genotypes have been identified using 12 SSR markers. In this, 21 polymorphic alleles were found in the studied set. The Nei and Fst indices revealed the moderate differences between the Chelyabinsk and Karaganda populations and a high similarity between other populations studied. The current survey defined the high similarity of leaf rust pathogen populations in West- Asian Russia and Northern Kazakhstan, assuming the existence of a single fungus population in the studied territories. In order to prevent the P. triticina epiphytoties on the adjacent territories of Russia and Kazakhstan, the constant updating of wheat varieties and higher genetic diversity are strongly recommended. In addition, the varieties should be grown according to the «mosaic distribution» scheme using optimal areas for genetically homogeneous varieties.