Leaf rust of wheat (Triticum aestivum L.) caused by the fungus Puccinia triticina (formerly P. recondita f. sp. tritici), is one of the most important foliar diseases of this crop. Breeding wheat cultivars with resistance to leaf rust is the most effective, economical and environmentally friendly method of disease control and was used in numerous wheat breeding programs worldwide (Kolmer, 1996). However, a gene-for-gene interaction exists between host resistance genes and pathogen avirulence genes in the wheat-P. triticina pathosystem and virulence shifts in the pathogen populations have reduced the effectiveness of a number of leaf rust resistance genes (Johnson, 2000), which increased the search of new resistant genes, not only in the cultivated gene-pool, but also in the wild relatives of wheat (Friebe et al. 1996; Valkoun, 2001).

The wild wheat species, Aegilops ventricosa Tausch (syn. Triticum ventricosum Ces), is an allotetraploid with the genome designation D^vD^vN^vN^v derived from the hybridization of the D genome from Ae. tauschii (coss.) Schmal and the N genome from T. uniaristatum (Vis.) Richter (Kimber and Zhao, 1983). Ae. ventricosa is the source of several disease resistance genes that are of agronomic importance and have been succesfully introgressed into wheat. These genes include Lr37, which confers resistance in wheat against leaf rust. This gene, located in a 2NS-2AS translocation (Bariana and McIntosh, 1993), was initially introgressed in the winter bread wheat VPM1 (Maia, 1967) and was used by breeders in different parts of the world (Robert et al. 1999; Mesterházy et al. 2000; Seah et al. 2000; Park et al. 2001; Stepien et al. 2003). Rust races with virulence to Lr37 have been identified in different countries (Mesterházy et al. 2000; Winzeler et al. 2000), but it still provides resistance to a wide range of races and is useful in combination with other resistance genes (Park and McIntosh, 1994; Park et al. 2001; Kolmer et al. 2005).

Greater knowledge on the identity of rust resistance genes present in cultivars that can be used as donors of resistance in wheat breeding programs could greatly improve the efficiency of developing resistant cultivars by using these genes per se or by stacking different resistant genes in a given cultivar (Sawhney and Joshi, 1996). In this context, there are no reports about the presence, frequency and origin of Lr37 in Argentinean wheat cultivars. Resistance gene postulation is a rapid method to hypothesize which resistance genes are present in a host genotype (Loegering et al. 1971). It is based on the gene-for-gene specificity between host resistance genes and pathogen avirulence genes. Host genotypes are evaluated with a well-characterized collection of pathogen isolates with different avirulence gene combinations. However, gene postulation can be complicated by interactions between resistance genes and it is best suited for resistance genes that are clearly expressed at the seedling stage (Kolmer, 1996). Resistance genes could also be postulated by testing host genotypes with DNA-based markers linked to resistant genes. This alternative approach overcome some of the problems associated with traditional gene postulation, such as gene interactions and the plant stage of gene expression (McCartney et al. 2005). For this reason, the objective of this work was to determine the presence of Lr37 resistance gene in a sample of 88 wheat cultivars registered in Argentina during the last 15 years by means of a molecular marker which is diagnostic of it.

Two pairs of primers were included in each PCR reaction. The primers VENTRIUP-LN2 developed by Helguera et al. (2003) were used to detect the 2NS fragment from Ae. ventricosa, that yield a 259-bp band. Since the long chromosomal fragment (25-38 cM) from Ae. ventricosa does not recombine with the bread wheat chromosomes, the resistance genes located in the 2NS segment are transferred together and are completely linked to markers developed within this segment (Robert et al. 1999; Helguera et al. 2003). In addition, the primers for the microsatellite marker GWM400 (Röder et al. 1998) were used to evaluate the quality of the DNA and the presence of PCR reaction inhibitors. These last primers amplify a fragment of about 150-bp.

The 259-bp PCR product from primers VENTRIUP-LN2 was observed in 4 out of 88 cultivars tested and in the positive checks VPM1 and Balthazar. The other cultivars and the two negative controls, on the other hand, did not amplify this diagnostic fragment. In fact, all of them presented only one PCR amplification product corresponding to different alleles of the microsatellite locus Xgwm400, used as an internal control of the PCR reaction.

The four cultivars which carry the translocated 2NS-2AS chromosome (Baguette 10, Baguette 12, Baguette 5 Sur and Baguette 11 Premium) were registered by the same breeding company (Nidera S.A.) in 1999, 2001 and 2004, and all of them have European germplasm in their genealogy. This is not surprisingly because VPM1 (the original line which carry the 2NS chromosome segment) was developed and used intensively in France and other European countries. As a matter of fact, the Lr37 resistant gene was identified, by means of gene postulation or molecular markers, in different cultivars registered in UK, the Czech Republic, France and Poland (Winzeler et al. 2000; Singh et al. 2001; Blaszczyk et al. 2004). The frequency of this gene in UK cultivars, for example, reached 26.6% by 2001 (Park et al. 2001). Cultivars registered in Argentina by other companies and institutions traced their origin to Argentinean, Uruguayan, Brazilian and Mexican wheat germplasm, where the deployment of the gene Lr37 was not reported.

To the best of our knowledge this is the first report of the presence of Lr37 in registered South American cultivars. Its identification in high yielding and adapted cultivars contribute to enrich an already broad genetic base for resistance to leaf rust in Argentinean wheat germplasm. Moreover, taking into account that Lr37 is linked to the genes Sr38, Yr17 and Cre5 (Bariana and McIntosh, 1993; Jahier et al. 1996; Seah et al. 2000) which confer resistance to stripe rust (Puccinia striiformis West. F. sp. tritici), stem rust (Puccinia graminis Pers. f. sp. tritici Eriks and E. Henn.) and cereal cyst nematode (Heterodera avenae Woll.) respectively, indicates that this introgressed chromosome fragment can be highly useful in developing new wheat varieties.

BARIANA, H.S. and MCINTOSH, R.A. Cytogenetic studies in wheat XIV. Location of rust resistance genes in VPM1 and their genetic linkage with other disease resistance genes in chromosome 2A. Genome, 1993, vol. 36, no. 3, p. 476-482.

BLASZCZYK, Lidia; CHELKOWSKI, Jerzy; KORZUN, Victor; KRAIC, Jan; ORDON, Frank; OVESNA, Jaroslava; PURNHAUSER, Laszlo; TAR, Melinda and VIDA, Gyula. Verification of STS markers for leaf rust resistance genes of wheat by seven European laboratories. Cellular and Molecular Biology Letters, 2004, vol. 9, no. 4b, p. 805-817.

FRIEBE, B.; JIANG, J.; RAUPP, W.J.; MCINTOSH, R.A. and GILL, B.S. Characterization of wheat-alien translocations conferring resistance to diseases and pests: current status. Euphytica, January 1996, vol. 91, no. 1, p. 59-87. [CrossRef]

HELGUERA, M.; KHAN, I.A.; KOLMER, J.; LIJAVETZKY, D.; ZHONG-QI, L. and DUBCOVSKY, J. PCR assays for the Lr37-Yr17-Sr38 cluster of rust resistance genes and their use to develop isogenic hard red spring wheat lines. Crop Science, September-October 2003, vol. 43, no. 5, p. 1839-1847.

JAHIER, J.; TANGUY, A.M.; ABÉLARD, P. and RIVOAL, R. Utilization of deletions to localize a gene for resistance to the cereal cyst nematode, Heterodera avenue, on an Aegilops ventricosa chromosome. Plant Breeding, September 1996, vol. 115, no. 4, p. 282-284. [CrossRef]

JOHNSON, R. Classical plant breeding for durable resistance to diseases. Journal of Plant Pathology, 2000, vol. 82, no. 1, p. 3-7.

KIMBER, G. and ZHAO, Y.H. The D genome of the Triticeae. Canadian Journal of Genetics and Cytology, 1983, vol. 25, p. 581-589.

KOLMER, J.A. Genetics of resistance to wheat leaf rust. Annual Review of Phytopathology, September 1996, vol. 34, p. 435-455. [CrossRef]

KOLMER, J.A.; LONG, D.L. and HUGHES, M.E. Physiologic specialization of Puccinia triticina on wheat in the United States in 2003. Plant Disease, November 2005, vol. 89, no. 11, p. 1201-1206. [CrossRef]

LOEGERING, W.Q.; MCINTOSH, R.A. and BURTON, C.H. Computer analysis of disease data to derive hypothetical genotypes for reaction of host varieties to pathogens. Canadian Journal of Genetics and Cytology, 1971, vol. 13, p. 742-748.

MAIA, N. Obtention des blés tendres resistants au pietin-verse par croisements interspecifiques blés X Aegilops. Comptes Rendus des Séances de l'Académie d'Agriculture de France, 1967, vol. 53, p. 149-154.

MCCARTNEY, C.A.; SOMERS, D.J.; MCCALLUM, B.D.; THOMAS, J.; HUMPHREYS, D.G.; MENZIES, J.G. and BROWN, P.D. Microsatellite tagging of the leaf rust resistance gene Lr16 on wheat chromosome 2BSc. Molecular Breeding, May 2005, vol. 15, no. 4, p. 329-337. [CrossRef]

MESTERHÁZY, A.; BARTOS, P.; GOYEAU, H.; NIKS, R.E.; CSOSZ, M.; ANDERSEN, O.; CASULLI, F.; ITTU, M.; JONES, E.; MANISTERSKI, J.; MANNINGER, K.; PASQUINI, M.; RUBIALES, D.; SCHACHERMAYR, G.; STRZEMBICKA, A.; SZUNICS, L.; TODOROVA, M.; UNGER, O.; VANCO, B.; VIDA, G. and WALTHER, U. European virulence survey for leaf rust in wheat. Agronomie, November 2000, vol. 20, no. 7, p. 793-804. [CrossRef]

PARK, R.F. and MCINTOSH, R.A. Adult plant resistances to Puccinia recondita f. sp. tritici in wheat. New Zealand Journal of Crop and Horticulture Science, February 1994, vol. 22, p. 151-158.

PARK, R.F.; GOYEAU, H.; FRIEDRICH, G.F.; BARTOS, P. and ZELLER, F.J. Regional phenotypic diversity of Puccinia triticina and wheat host resistance in western Europe, 1995. Euphytica, January 2001, vol. 122, no. 1, p. 113-127. [CrossRef]

ROBERT, Oliver; ABELARD, Christine and DEDRYVER, Françoise. Identification of molecular markers for the detection of the yellow rust resistance gene Yr17 in wheat. Molecular Breeding, March 1999, vol. 5, no. 2, p. 167-175. [CrossRef]

RÖDER, Marion S.; KORZUM, Victor; WENDEHAKE, Katja; PLASCHKE, Jens; TIXIER, Marie-Hélène; LEROY, Philippe and GANAL, Martin W. A microsatellite map of wheat. Genetics, August 1998, vol. 149, no. 4, p. 2007-2023.

SAWHNEY, R.N. and JOSHI, B.C. Genetic research as the valid base of strategies for breeding rust resistant wheats. Genetica, May 1996, vol. 97, no. 3, p. 243-254. [CrossRef]

SEAH, S.; SPIELMEYER, W.; JAHIER, J.; SIVASITHAMPARAM, K. and LAGUDAH, E.S. Resistance gene analogs within an introgressed chromosomal segment derived from Triticum ventricosum that confers resistance to nematode and rust pathogens in wheat. Molecular Plant-Microbe Interactions, March 2000, vol. 13, no. 3, p. 334-341.

SINGH, D.; PARK, R.F. and MCINTOSH, R.A. Postulation of leaf (brown) rust resistance genes in 70 wheat cultivars grown in the United Kingdom. Euphytica, January 2001, vol. 120, no. 2, p. 205-218. [CrossRef]

STEPIEN, Lukasz; GOLKA, Lidia and CHELKOWSKI, Jerzy. Leaf rust resistance genes of wheat: identification in cultivars and resistance sources. Journal of Applied Genetics, 2003, vol. 44, no. 2, p. 139-149.

VALKOUN, J.J. Wheat pre-breeding using wild progenitors. Euphytica, May 2001, vol. 119, no. 1-2, p. 17-23. [CrossRef]

WINZELER, Michael; MESTERHAZY, Akos; PARK, Robert F.; BARTOS, Pavel; CSOSZ, Maria; GOYEAU, Henriette; ITTU, Mariana; JONES, Elwyn; LOSCHENBERGER, Franziska; MANNINGER, Klara; PASQUINI, Marina; RICHTER, Klaus; RUBIALES, Diego; SCHACHERMAYR, Gabriele; STRZEMBICKA, Anna; TROTTET, Maxime; UNGER, Otto; VIDA, Gyula and WALTHER, Ursula. Resistance of European winter wheat germplasm to leaf rust. Agronomie, November 2000, vol. 20, no. 7, p. 783-792. [CrossRef]

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