No abstract

The individual use of single race-specific resistance genes with major phenotypic effects has rarely provided lasting resistance. However, breeding and combining or pyramiding of resistance genes into individual cultivars has had considerable success, particularly in situation where the pathogen does not reproduce sexually, as in the case of wheat leaf rust pathogen. Within international leaf rust of wheat investigations it was necessary, to create by breeding new resistant wheat lines to Puccinia recondita tritici for differentiation of pathogen population, as well as for sources of resistance in European-Mediterranean regions. In the beginning 18 donors of resistance had been selected after an extensive screening test of several International Rust Nurseries, to be crosses with recur- rent parents varieties Princ and Starke. These tests proved that in those lines were present new resistant genes. Eighth genetically different hybrids of the first back-cross had been selected and tested in the seedling stage with three international pathogen cultures (YU-13-19-1; H-13-9-1 and C2-13-Ar-3). Considerable influence of recurrent parent to the number of resistant genes in donors used was demonstrated. On the other side, it was established considerable influence of the pathogen culture to the number of resistant genes in donors used. The same crossing combinations tested with one pathogen culture results in presence of two resistance genes, but with another culture three or one resistant gene. In order to enhancement resistance and pyramiding genes in these hybrids, eight selected the most interesting lines have been crossed with only effective isogenic containing the strong genes Lr9, Lr19 and Lr24.The genetic analysis of twenty two crossing combinations have been realized by testing with three pathotypes of Puccinia recondita tritici ( Bg.s. 12/89; Is.w 8/89 and Chl.w. 14/89). On the base of different segregation ratios of all crossing combinations it was proved that no one of the resistant donors contained the strong resistant genes used. It means that our hybrid lines contained resistant genes from the donors and in addition three strong resistant genes Lr9, Lr19 and Lr24

The main objective within new approach in international pathogenicity surveys of Puccinia recondita tritici was to provide genetically diverse sources of resistance (wheat lines with pyramiding resistant genes) to be used in a survey of wheat leaf rust pathogen in European-Mediterranean regions and to search for and document pathogenicity of P. recondita tritici cultures useful in differentiating sources of resistance. Emphasis is placed on sources of resistance and their usefulness rather than on description of fungus populations. In this international survey new methods have been applied containing Central Field Nursery, Central Seedling Tests, Cooperative Seedling Tests and Regional Field Nurseries (ELRWN-European Leaf Rust of Wheat Nursery). The results have been reported from one year of investigations. ELRWN contained 20 winter wheat hybrid lines with pyramiding resistant genes including strong ones Lr9, Lr19 and Lr24. In addition, 16 spring wheat lines were included, as control lines were Lr9, Lr18, Lr19, Lr24 and Lr14. In that year ELRWN have been realized in 13 countries and cooperative seedling test in 8 countries using 22 pathotypes of P. recondita tritici. The best results obtained by the winter wheat lines NS-66/5'Lr24, NS-77/2'Lr19, NS- 37/2'Lr19 and spring wheat lines 647-CMA-14793 and 26TH-ESWYT-10. The results have shown loosing almost complete resistance of Lr9 and Lr24, but much less Lr19

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The individual use of single race-specific resistance genes with major phenotypic effects has rarely provided lasting resistance. However, breeding and combining or pyramiding of resistance genes into individual cultivars has had considerable success, particularly in situations in which the pathogen does not reproduce sexually, as in the case of wheat leaf rust pathogen. In European-Mediterranean region perfomed international investigations of wheat leaf rust proved that breeding of new lines of wheat resistant to Puccinia triticina Eriks. for differentiation of pathogen population, as well as for sources of durable resistance is necessary. Breeding of such resistant lines has proved necessary due to the unsatisfatory survey results of these regions on standard isogenic Lr lines. It has become clear that these regions needed new, more efficient differential resistance genes, as well as sources of resistance. In the beginning, after extensive screening tests of several International Rust Nurseries, 18 donors of resistance had been selected as crosses with recurrent parents' varieties Princ and Starke. These hybrid lines had been comparatively tested with twenty six Lr single gene lines using twenty especially virulent cultures of P. triticina in order to check the presence of these known Lr genes in our hybrid lines. Considerable influence of recurrent parent to the number of resistant genes in used donors was demonstrated. On the other hand, considerable influence of the pathogen culture was established to the number of resistance genes in used donors. In order to enhance resistance and pyramiding genes in these hybrids, the most interesting selected eight lines have been crossed with only effective isogenic ones, containing the strong genes Lr9, Lr19 and Lr24. On the basis of different segregation rations of all crossing combinations it was proved that no one of resistant donors contained the applied strong resistant genes. It means that our hybrid lines contained resistant genes from the donors, as well as three strong resistant genes Lr9, Lr19 and Lr24