%D 2003 %0 ARTICLE %T Identification and fine mapping of Pi33 , the rice resistance gene corresponding to the Magnaporthe grisea avirulence gene ACE1 . %J Theor . Appl . Genet . %V 107 ( 6 ) %P 1139-47 %A Berruyer R %A Adreit H %A Milazzo J %A Gaillard S %A Berger A %A Dioh W %A Lebrun MH %A Tharreau D %M pub12838393 %X Rice blast disease is a major constraint for rice breeding . Nevertheless , the genetic basis of resistance remains poorly understood for most rice varieties , and new resistance genes remain to be identified . We identified the resistance gene corresponding to the cloned avirulence gene ACE1 using pairs of isogenic strains of Magnaporthe grisea differing only by their ACE1 allele . This resistance gene was mapped on the short arm of rice chromosome 8 using progenies from the crosses IR64 ( resistant ) x Azucena ( susceptible ) and Azucena x Bala ( resistant ) . The isogenic strains also permitted the detection of this resistance gene in several rice varieties , including the differential isogenic line C101LAC . Allelism tests permitted us to distinguish this gene from two other resistance genes [ Pi11 and Pi-29 ( t ) ] that are present on the short arm of chromosome 8 . Segregation analysis in F ( 2 ) populations was in agreement with the existence of a single dominant gene , designated as Pi33 . Finally , Pi33 was finely mapped between two molecular markers of the rice genetic map that are separated by a distance of 1 . 6 cM . Detection of Pi33 in different semi-dwarf indica varieties indicated that this gene could originate from either one or a few varieties .