New Tools For Resistance Gene Characterisation In Rice.

Rice progeny used for the construction of genetic maps could be used to identify and map the resistance genes present in their parental cultivars. Using a targe number of isolates avirulent on at least one of the two parents, such crosses facilitate the mapping of new blast resistance genes. We inoculated rice progeny from the cross IR64 x Azucena using different Magnaporthe grisea isolates with differential responses on the two parental cultivars. QTL mapping allowed the identification of 7 independent loci conferring resistance to these isolates that could correspond to specific 7 resistance genes. Some of these QTL/gene mapped at chromosomal locations where 170 resistance gene were previously located. We used a similar approach to map the resistance gene corresponding to avr1-Irat7, an avirulence gene recently cloned (MH Lebrun personal communication). The two strains, 2/0/3 virulent on Bala and Azucena, and PH14 virulent on IR64 and Azucena, were transformed with the cloned avirulence gene avr1-lrat7. For the cross Bala x Azucena, we inoculated on all progeny both 2/0/3 and its avr1-lrat7 transformant being avirulent Bala. For the cross IR64 x Azucena, we inoculated on all progeny both the isolate PH14 and its avr1-lrat7 transformant being avirulent on IR 64. The analysis of cosegregation between the resistance gene specific of avr1-lrat7 transformants and rice molecular markers indicates that it is located on chromosome 8 in both crosses.