Institute for Plant Protection, Department of Mycology and Phytopathology, Podbeisky str., 3. 189620, Saint-Petersburg, Pushkin, Russia

Background and objective
Wheat leaf rust, caused by Puccinia recondita f.sp.tritici, occurs annually throughout most wheat-growing areas of Russia and sometimes results in considerable yield losses. High variability of the pathogen population demands continuity of the breeding process. In order to be ahead of constantly changing pathogen populations it is necessary to maintain genetic diversity of resistance sources.

Materials and methods
The aim of these studies was to identify leaf rust resistance genes (Lr) in 35 cultivars and improved lines (spring wheats: Pringlial (France), lnia 66, 474546, (Mexico), CNT N7 (Brasil), Estanzuelia (Argentina), Mamba (Tanzania), Maya Tovom (Zambia), PBV 65, HD 2402, HW 741 (India); winter wheats: 1) NS675, 2) 4204 (Yugoslavia), 3) M357-1, 4) 3357-58 (Bulgaria), 5) N 30432 (Romania), 6) Fl-1331, 7) F2H-296 (Hungary), 8) Purdue 6693, 9) Ponca, 10) Frederick, 11) STW 646252, 12) Co 725049, 13) Co 725055, 14) Co 725082, 15) Parker 5, 16) Parker, 17) TAM 106 (USA), 18) 96190, 19) AK 60634, 20) IWWPMP 15186, 21) IWWRN 208185, 22) F5H70128-113-4, 23) TP 420-72, 24) IWWRN 144183 (Bulgaria), 25) TPR 354 (UK). These wheats are resistant to Russian populations of P. recondita in the seedling and adult plant stages. The genetic control of resistance was determined from segregation in F2 and F3 generations from crosses of resistant genotypes with susceptible Saratovskaya 29 or Bezostaya 1 and with Thatcher lines carrying Lr9, Lr19, Lr23, Lr24. Crosses between genotypes N1-5, N5-N17, N18-N25 were performed in an incomplete diallel scheme. The adult plant resistance was tested under field conditions. A laboratory method based on application of benzimidazole solution for seedling tests was used [1].

Results and conclusions
The winter wheat sample 4204 has the Lr23; NS675, N357-1, 3357-58 have a different resistance genes non-identical to genes of Thatcher lines (Lr9, Lr19,Lr23, Lr24). Cv. Parker has one recessive gene (Lrpar). Segregation was absent in the F2 and F3 Of cross Parker with Parker 5, TAM 106, FI-1 331, F2H-296. There was no segregation in the F2 and F3 Of crosses involving cvs. Co 725049, Co 725055, Co 725082, Parker 5, TAM 106, Fl -1 331 and F2H296. It is proposed to designate the dominant gene common for cultivars of this group LrCol. Segregation was also absent in the F2 and F3 of the cross between cv. Frederick and TAM 106; the recessive gene common for this group Lrfred. Cvs. Ponca, STW 646252 have different genes which are not identical to genes of the other cultivars from the USA used in our experiments. Ponca has two complementary dominant genes. In the USA its resistance provides gene Lr3, that is absolutely ineffective in Russia. It is known that cultivars TAM 106 and Parker are defended in USA by Lrlp, that is only partially effective in Russia [2]. In our country these cultivars are resistant owing to the other genes. Purdue 6693 has a gene tightly linked with Lr19, N 30432 has Lr19 or a gene closely linked with it. The absence of segregation in crosses N 30432 and Purdue 6693 was determined, but a pathogen isolate virulent to Purdue 6693 and aviruient to Thatcher Lr19 and N 30432 was discovered. Most of the winter wheat accessions originated from Bulgaria (N18-N25) contents gene Lr23. The samples 96190 (Bulgaria) and TPR 354 (UK) have a genes non-identical Lr9, Lr19, Lr23, Lr24. The most studied wheat samples can serve as a sources of leaf rust resistance in breeding.

1. Mikhailova LA, Kvitko KV, 1970. Mycologia and Phytopatologia (Russian) 4, 269-273.
2. Mcintosh RA, Wellings CS, Park RF, 1995. Wheat Rusts. An Atlas of Resistance Genes. CSIRO, Australia.