Accumulations of genes for durable resistance to wheat leaf rust pathogen

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.

Testing of wheat to durable resistance and survey approach for Puccinia recondita tritici

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.

Locating the Agropyron segment in wheat–Agropyron transfer no. 12

Twelve lines of wheat (Triticum aestivum L.) were originally identified as having a segment of Agropyron elongatum chromatin carrying a gene for resistance to leaf rust (Puccinia recondita tritici) transferred to wheat chromosome 7D. By studying the chromosome pairing of one of these lines, transfer no. 12, with telosomes 7AL, 7AS, 7BL, 7BS, 7DL, 7DS, and 7AgS, it was determined that the Agropyron chromatin was carried on the long arm of wheat chromosome 7A rather than 7D. This determination was confirmed by acetocarmine–N-banding. Key words: Triticum aestivum, Agropyron elongatum, transfer lines, Puccinia recondita tritici, telosomic analysis.

Complementary genes for reaction to Puccinia recondita tritici in Triticum aestivum. II. Cytogenetic studies

Two complementary genes, A and B, conferring resistance to Puccinia recondita tritici in various wheats were located in chromosomes 4Aβ and 3BS, respectively. In one study gene B showed recombination of 33.6 ± 4.1% with the centromere, and was independent in a second study. Gene B was the same as that designated Lr27. A new designation, Lr31, is proposed for gene A. Both Lr27 and Lr31 must be present for the expression of resistance.Key words: leaf rust, monosomic analysis, aneuploids, wheat.

Complementary genes for reaction to Puccinia recondita tritici in Triticum aestivum. I. Genetic and linkage studies

Although confirmed instances of complementary genes for rust resistance are rare, two such genes designated A and B for seedling leaf rust resistance were identified in 'Gatcher' and certain other wheats. The two complementary genes in 'Gatcher' were separated in susceptible lines which, when intercrossed, again produced resistant progenies with the specificity of 'Gatcher.' The substitution of a chromosome 3B pair from seedling susceptible 'Hope' into seedling susceptible 'Chinese Spring' resulted in lines displaying similar leaf rust responses to 'Gatcher.' Resistant segregates occurred in segregating populations from crosses of several Sr2-bearing leaf rust susceptible wheats with 'Chinese Spring.' Hence 'Chinese Spring' carried one (A) of the complementary genes, whereas the second gene (B) was very closely linked with Sr2 (r < 0.5%) and was present in a wide range of wheats possessing Sr2. Two wheats carrying gene B lacked Sr2.Key words: leaf rust, stem rust, specificity, wheat.

Slow rusting and tolerance to rusts in wheat. II. The progress and effects of epidemics in Puccinia recondita tritici in selected wheat cultivars

The progress and effects of epidemics of leaf rust (Puccinia recondita Rob, ex Desm. f, sp. tritici Erikss. & Henn.) have been examined in 45 wheat cultivars over two seasons. The epidemics in each cultivar were compared by various measures and by pattern analysis. The cultivars were separated into groups ranging from highly resistant to highly susceptible with intermediate groups possessing various levels of slow-rusting ability. Cvv. Hopps, Warchief, Huguenot, Pusa 80-5c, Dural, Warput, Koolisie and Puglu were found to possess useful levels of slow-rusting ability. Fast rusting was conspicuous in Gabo and its derivatives Mendos, Mengavi, Gamenya and Gamut. The desirability of not perpetuating this defect is discussed.