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DEVELOPMENT AND USE OF SCAR (SEQUENCE CHARACTERIZED AMPLIFIED REGIONS) TO ANALYSE POPULATIONS OF MAGNAPORTHE GRISEA
DEVELOPMENT AND USE OF SCAR (SEQUENCE CHARACTERIZED AMPLIFIED REGIONS) TO ANALYSE POPULATIONS OF MAGNAPORTHE GRISEA O SOUBABERE 1 , D THARREAU 1 , W DIOH 2, MH LEBRUN 3, and JL NOTTEGHEM 4 1 CIRAD, BP5035, 34032 Montpellier, FRANCE; 2 Universit6 Paris-Sud, 91405 Qrsay, France; 4 CNR~RPA, BP9163, 69623 Lyon, France; 4 ENSAM, 2 place viala, 34060 Montpellier, France. Background and objectves Magnaporthe grisea (Hebert) Ban is responsible for the Rice Blast disease. This Ascomycete fungus is haploid and only its asexual form ( Pyricularia grisea) has been observed in the fields. Up to date, population studies of the pathogen were carried out with RFLP [1, 2] and RAPD markers. These techniques brought important knowledge on populations at the field and country level. But, these markers are not well adapted to world population's comparison. Thus, we developed new molecular tools, i.e. SCAR markers (Sequence Characterized Amplified Regions), to study populations of M. grisea. Results and conclusion Twenty markers were set up using RAPD markers or available gene sequences. Fifteen of these markers have been used to characterize a sample of 64 isolates collected on rice worldwide (Africa, North and South America, Asia and the Mediterranean Basin). This analysis shows that the sample studied is made of 8 groups, three of them being represented by only one isolate. Groups 1 and 2 gather most of the isolates. Group I is made of 26 isolates mainly of mating type Mat1 .1 and originating from Asia, Americas and Mediterranean Basin. Group 2 gathers 22 isolates mainly of mating type Mat1 .2 and originating from Asia, Americas and Africa. The population of each continent is differentiated. Results suggest that the level of differentiation could be linked to genetic diversity of the host. Thus, rice could act as a major factor of population structuration of the pathogen. Genetic diversity was the highest in Asia. Isolates from Asia where found in the 5 main groups and some isolates from Asia have the same haplotype as isolates from Americas, Mediterranean Basin and Africa. All these results suggest that the centre of diversification of the pathogen could be situated in Asia and that migration to other continents occurred. Movements of infected rice seeds might have played a major role in the spreading of the pathogen. These preliminary results obtained with SCAR markers bring new insight on populations of the Rice Blast fungus on a worldwide scale. References 1. Levy M, Romao J, Marchetti MA, Hamer JE, 1991. The Plant Cell 3, 95-102. 2. Roumen E, Levy M, Notteghem JL, 1997. European Journal of Plant Pathology, 103, 363-371.