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Pyrenophora tritici-repentis (Died.) Drechs. (syn. P. trichostoma (Fr.) Fckl.), anamorph: Helminthosporium tritici-repentis (syn. Drechslera tritici-repentis (Died.) Shoem.) is the causal agent of tan spot of wheat (Triticum aestivum L.). Tan spot of wheat has been identified in major wheat growing areas throughout the world and it is a disease of significant economic importance (4,5,13). The disease was first detected in the US in 1940 and has increased in incidence and severity to the present (4,5,13). Yield losses attributed to this disease have ranged from 3 to 50% in the Central Plains of the US and Canada (10,15). Increases in disease incidence have been attributed to changes in cultural practices including, shifts from conventional tillage to conservation- and zero-tillage practices, shorter rotations and continuous wheat cultivation, and the culture of highly susceptible cultivars. In addition, the change from stubble burning to its retention is believed to be the cause of the increased incidence in areas of the world (1,6,9,12,14). Interestingly, areas that have reported a decline in leaf and stem rusts due to the release of resistant germplasm have experienced an increase in the predominance of tan spot (7). Foliar fungicides can be effective in the control of the disease, but costs may be prohibitive and economic returns are not consistent (5). Due to the wide-ranging occurrence of the disease and its potential destruction, International Tan Spot Workshops are held on a regular basis to strengthen research partnerships directed at reducing yield losses and developing strategies for disease control.

Experimentally, Pyrenophora tritici-repentis is a necrotrophic pathogen that displays a complex race structure that involves the production of multiple, race-specific virulence factors (or host-selective toxins [HSTs]) that in contrast to most HSTs are predominantly, readily genetically tractable as single proteins. This form of race structure is truly gene-for-gene, but displays an inverse relationship to the classically defined gene-for-gene interactions that typically involves biotrophic or hemibiotrophic pathogens (13,18). Tan spot of wheat presents not only a disease interaction of significant economic impact, but also is a disease interaction with the potential to become a ?model? gene-for-gene system for understanding pathogen virulence and host disease susceptibility. The genus Pyrenophora includes a number of significant pathogens that reflect the type of lifestyle and pathogenic adaptations of a large number of related, economically and historically significant fungi.

The strain chosen for sequencing is designated Strain Pt-1C-BFP of race 1. Race 1 is the most prevalent race found in both the US and throughout the world and most of the molecular genetics and applied research has been conducted on race 1 isolates. The first host-selective, protein toxin, Ptr ToxA, was characterized from this race as well (2,16,17,19). Currently, this race is known to produce at least 2 HSTs (1 protein HSTs [Ptr ToxA] and one partially characterized as a low-molecular weight molecule [Ptr ToxC]) (4,5,8,13). In addition, data indicate that there are additional protein toxins produced by this race (17).

Pt-1C-BFP is a fast-growing subculture of isolate Pt-1C. Pt-1C is commonly available and has been used in many laboratories. This isolate grows well both in culture and in planta and has been used in many of the molecular genetic studies. BFP (subculture Pt-1C), as well as, all isolates used for cDNA libraries in this project will be deposited in the Fungal Genetics Stock Center for Community access. All proper USDA/Aphis permits will be obtained.

 

1. Bailey, K. L. 1996. Diseases under conservation tillage system. Can. J. Plant Sci. 76:635-639

2. Ballance, G.M., L. Lamari, and C.C. Bernier. 1989. Purification and characterization of a host-selective necrosis toxin from Pyrenophora tritici-repentis. Physiol. and Molec. Plant Pathol. 35:203-213.

3. Batzoglou, S., D. B. Jaffe, K. Stanley, J. Butler, S. Gnerre, E. Mauceli, B. Berger, J. P. Mesirov, and E. S. Lander. 2002. ARACHNE: a whole-genome shotgun assembler. Genome Res 12: 177-89.

4. Ciuffetti, L.M. and R.P. Tuori. 1999. Advances in the Characterization of the Pyrenophora tritici-repentis-Wheat Interaction. Phytopathology 89:444-449.

5. De Wolf, E.D., R.J. Effertz, and L.J. Francl. 1998. Vistas of tan spot research. Can. J. Plant Pathol. 20:349-444.

6. Diaz de Ackermann, M. and Kohli, M. M. 1998. Research on Pyrenophora tritici-repentis tan spot of wheat in Uruguay. Pages 134-141 in: Helminthosporium Blights of Wheat: Spot Blotch and Tan Spot. E. Duveiller, H. J. Dubin, J. Reeves, and A. McNab, eds. Mexico, D.F.:CIMMYT.

7. Di Zinno, T., Longree, H., and Maraite, H. 1998. Diversity of Pyrenophora tritici-repentis isolates from warm wheat growing areas: Pathogenicity, toxin production, and RAPD analysis. Pages 302-311 in: Helminthosporium Blights of Wheat: Spot Blotch and Tan Spot. E. Duveiller, H. J. Dubin, J. Reeves, and A. McNab, eds. Mexico, D.F.:CIMMYT.

8. Effertz, R.J., S.W. Meinhardt, J.A. Anderson, J.C. Jordahl, and L.J. Francl. 2002. Identification of a chlorosis-inducing toxin from Pyrenophora tritici-repentis and the chromosomal location of an insensitivity locus in wheat. Phytopathology 92:527-533.

9. Freebairn, D. M. 1986. Stubble: the key to success. Queensland Agric. J. July-August, pp. 194- 195.

10. Hosford, R. M., Jr., Larez, C. R., and Hammond, J. J. 1987. Interaction of wet period and temperature on Pyrenophora tritici-repentis infection and development in wheats of differing resistance. Phytopathology 77:1021-1027.

11. Jaffe, D. B., J. Butler, S. Gnerre, E. Mauceli, K. Lindblad-Toh, J. P. Mesirov, M. C. Zody, and E. S. Lander. 2003. Whole-genome sequence assembly for mammalian genomes: Arachne 2. Genome Res 13: 91-6.

12. Krupinsky, J. M., Halvorson, A. D., and Black, A. L. 1998. Leaf spot diseases of wheat in a conservation tillage study. Pages 322-326 in: Helminthosporium Blights of Wheat: Spot Blotch and Tan Spot. E. Duveiller, H. J. Dubin, J. Reeves, and A., McNab, eds. Mexico, D.F.:CIMMYT.

13. Strelkov SE, Lamari L. 2003. Host-parasite interactions in tan spot [Pyrenophora tritici-repentis] of wheat. Can J Plant Pathol 25:339?349.

14. Sutton, J. C., and Vyn, T. J. 1990. Crop sequences and tillage practices in relation to diseases of winter wheat in Ontario. Can. J. Plant Pathol. 12:358-368.

15. Sykes E.E. and C.C. Bernier. 1991. Qualitative inheritance of tan spot resistance in hexaploid, tetraploid, and diploid wheat. Can. J. Plant Pathol. 13:38-44.

16. Tomas, A., G.H. Feng, G. R. Reech, W.W. Bockus, and J.E. Leach. 1990. Purification of a cultivar-specific toxin of Pyrenophora tritici-repentis, causal agent of tan spot of wheat. Mol. Plant-Microbe Interact. 3:221-224.

17. Tuori, R.P., T.J. Wolpert, and L.M. Ciuffetti. 1995. Purification and immunological characterization of toxic components from cultures of Pyrenophora tritici-repentis. Mol. Plant-Microbe Interact. 8:41-48.

18. Wolpert, T.J., L. D. Dunkle, and L.M. Ciuffetti. 2002. Host-selective Toxins and Avirulence Determinants: What?s in a Name. Ann. Rev. Phytopathol. 40:252-285.

19. Zhang, H.-F., L.J. Francl, J.G. Jordahl, and S.W. Meinhardt. (1997). Structural and physical properties of a necrosis-inducing toxin from Pyrenophora tritici-repentis. Phytopathology 87, 154-160.