Genetic Analysis Of Avirulence Genes And Construction Of BAC Library Of Magnaporthe Grisea FJ95054B

The ascomycetous fungus Magnaporthe grisea (anamorph Pyricularia grisea) causes rice blast, one of the most important diseases of rice. For most rice-growing areas, rice blast disease management relies on the frequent application of new resistant rice cultivars. However, M.grisea is able to rapidly overcome host resistance because of its genetic diversity and complexy. And the sexual generation of M.grisea is vital to the genetic analysis, mapping and functional studying of genes related to pathogenicity. This paper presents the genetic analysis of 79 F₁ progeny isolates of M.grisea obtained from the cross of FJ95054B and GUY11, and the construction of a BAC (bacterial artificial chromosome) library of FJ95054B, which will facilitate the map-based cloning and further functional studying of avirulence genes.To study the virulence difference between FJ95054B and GUY11, the two isolateswere inoculated on 33 ( 24 IRBL and 9 Japanese) known resistance gene rice cultivars.The results showed that FJ95054B was virulent to 3 rice cultivars, and GUY11 was virulent to 26 of 33 rice cultivars. On only 6 of 33 rice cultivars, the two isolates showed the same virulence or avirulence. Therefore, there was much difference between FJ95054B and GUY11 on pathogenicity to rice cultivars. Co39 NILS (near isogenic lines, C101LAC Pi-1(t), C101A51 Pi-2(t), C104PKT Pi-3(t), C101PKT Pi-4a, C105TTP-4L-23 Pi-4b, CO39) were used to test the virulence of FJ95054B and GUY11 strains. Based on the result, it is assumed that FJ95054B has Avr-Pi1, Avr-Pi2 and Avr-Pi4a avirulence genes, but GUY11 only has Avr-Pi4b avirulence gene .The segregation of avirulence/virulence was studied in 79 F₁ progeny isolates of M. grisea from the cross between FJ95054B and GUY11. The segregation ratios of avirulence and virulence on C101 LAC Pi-1(t), C101A51 Pi-2(t), C101PKT Pi-4a in the 79 F₁ progeny isolates fit 1:1 statiscally, and there were 6 recombinant F₁ progeny isolates among these three avirulence loci. The results indicated that Avr-Pil, Avr-Pi2 and Avr-Pi4a in FJ95054B were three tightly linked but independent loci. And the segregation ratio of avirulence and virulence on C105TTP-4L-23 Pi-4b in the 79 F₁ progeny isolates fit 3:1.Map-based cloning is the main method to clone avirulence genes in fungal...