INBA   12521
INSTITUTO DE INVESTIGACIONES EN BIOCIENCIAS AGRICOLAS Y AMBIENTALES
Unidad Ejecutora - UE
capítulos de libros
Título:
Pyrenophora tritici repentis, the causal agent of tan spot: a review of intraspecific genetic diversity
Autor/es:
MORENO M. V.; STENGLEIN S.A.; PERELLÓ A.E.
Libro:
Genetic Diversity / Book 2
Editorial:
INTECH
Referencias:
Año: 2011; p. 297 - 330
Resumen:
Pyrenophora tritici-repentis (Ptr) (Died) Drechs., anamorph  Drechslera tritici-repentis (Died.) Shoemak., is a facultative pathogen that is responsible for the foliar disease tan spot of wheat (Triticum aestivum L.). The tan spot of wheat is a destructive potential disease identified in major wheat-growing areas throughout the world. The disease was reported as the fastest-spreading disease in the Southern Cone region of South America¸ especially under minimum/zero tillage practices and monoculture. Wheat seeds, straw and collateral hosts are the principal sources of tan spot inoculum.  In addition, several authors consider the straw as the principal source of P. tritici-repentis  inoculum. Interestingly, collateral hosts of P. tritici-repentis could play an important role as a source of primary inoculum between growing seasons, as a source of genetic variation, and as a reservoir of a fungal population genetically different from that prevalent on wheat. Tan spot has been found in several countries worldwide like Australia, Argentina, Asia, Belgium, Brazil, Bolivia, Canada, Colombia, Czech Republic, Denmark, Ecuador, France, Hungary, Pakistan, Paraguay, Peru, Poland, United States of America, Ucrania and Uruguay. Over the last 20 years studies have been focused on different aspects of host-pathogen interaction. The P. tritici-repentis -wheat pathosystem is a complex pathosystems. A great deal, of the host genetic resistance and physiological variation in the pathogen has been explained. These studies have been well documented in several papers. It known that the pathogen is highly variable in its morphologic, pathogenic and genetic characteristics. Up to the present, eight races of pathogens ha been identified, based on the type of symptoms on a standard set of wheat cultivars and lines. This classification is base on the interaction with the plant host (wheat). P. tritici-repentis produces five different host-specific toxins. Although five toxins have been reported, most studies were focused on three (Ptr ToxA, Ptr ToxB, and Ptr ToxC). Among these toxins, the Ptr ToxA and Ptr ToxB have been identified, characterized and their respective coding genes have been cloned.  Ptr ToxC has been currently identified but it has not been characterized because it is not readily produced in culture filtrates. Moreover, two toxins have been reported called Ptr ToxD, but the advances are unknown. It is known that Ptr Tox A is produced by races 1, 2, 7, and 8; Ptr ToxB is produced by races 5, 6, 7, and 8; and Ptr Tox C is produced by races 1, 3, 6, and 8. Several works have been made over the last years focusing on the P. tritici-repentis race structure population and the virulence/avirulence within the different isolates of the pathogen. Interestingly, with the use of polymerase chain reaction (PCR) techniques, several studies have been intensified for the application of different molecular markets to detect P. tritici-repentis intraspecific genetic variability. In most cases this situation has developed from an attempt to justify the wide variation found in previous studies, with the aim to study the genetic variation of the pathogen population. The knowledge of the genetic structure and population diversity of the pathogen is important in the management of fungal diseases, especially, for the successful development of host resistance and effective integrated crop management. Several molecular markers have been used for the detection of variability in P. tritici-repentis population in different regions and countries. Among them, we can cite the enterobacterial repetitive intergenic consensus (ERIC) and repetitive extragenic palindromic (REP)-PCR, restriction fragment length polymorphisms (RFLP), random amplified polymorphic DNA (RAPD), amplified fragment length polymorphisms (AFLP), internal sequence simple repeat (ISSR), internal transcribe spacer (ITS). Recently, primers to detect the gene that codified for specific toxins Ptr ToxA, Ptr ToxB and Ptr toxb have been developed and used for many studies, and several works have enunciated that the classification in races of P. tritici-repentis based only on phenotypic symptoms is in disagreement with the obtained results of genotypic analysis. It is known that P. tritici-repentis has been cited as a homothallic fungus. In the field the sexual cycle is completed on the wheat straw, and several asexual cycles are produced on the leaf. Some works have studied the homothallic nature of P. tritici-repentis using the specific molecular markers for detection of the MAT genes. The aim of this chapter is to provide a comprehensive review and the current status of the different molecular markers used to detect intraspecific variation of P. tritici-repentis.