| The rice blast disease caused by Magnaporthe grisea (Hebert) Bar. continues to be the most destructive disease of rice, the primal crop for human consumption, dcspite decades of international research towards its control. it is crutial to better understand the fungal population genetics and molecular mechanism in rice-blast fungus interaction for us to manipulate the pathosystem in order to reduce losses. This paper presents the mating results of the fungal isolates from Fujian province, China, and genetic analysis of the random progenies of the cross 81 278ZB 15 and GUY 11 to know whether sexual recombination contributes to the disease complexity, and to analyze the genetic characteristics of mating type alleles, avirulence genes in the sexual generation. Five pair of mating type testers were crossed with 38 rice isolates from Fujian province. The fertility and mating type of the same isolates change with different testers used. This is caused by the different sexual capability and compatibility in different testers. Among all 5 pair of testers, GUY 11 and KA3 are the best to detect mating type MAT 1-1 and MAT 1-2 respectively, with which 227 rice isolates were mated, resulting in 80.2% of fertile isolates, and among the fertile isolates 81.9% are MAT1-2 and 18.1% are MAT1-1. To know the potential mating type of those sterile isolates in the nature population of M grisea and to test the mating type of the blast fungus more easily and efficiently, two pairs of PCR primers were designed to specifically amplify MAT1-1 and MAT1-2 alleles. The PCR amplification pattern of 207 rice isolates from Fujian province strongly correlative to the results obtained by using GUYI 1 and KA3. The fertile isolate 81278ZB15, which belongs to a dominant virulence type in the province, has different rep-PCR DNA fingerprints and virulence spectrum results suggested that genetic polymorphic and virulence spectrum of 81 278ZB 15 were greatly different than GUY11. 90 ascospores of the cross 81278ZB15 and GUY11 were randomly isolated. The ratio of MATI-2 to MAT1-1 is 62:21 tested by GUY1 1 and KA3, and 62:28 identified by PCR, which do not fit the 1:1 segregation. Based on their virulence on Co39 NILS (near isogenic lines, C1O1LAC Pi-1, C1OIA51 Pi-2, CIO4PKT Pi-3, C1O1PKT Pi-4a, C1O5TTP-4L-23 Pi-4b and Co39), it is assumed that 31278ZB15 has Avr-Pil, Avr-Pi2, Avr-Pi4a and Avr-Pi4b, but GUY1 1 only has Avr-Pi4b. The segregation of avirulent and virulent on C1O1LAC Pi-1, C1O1A51 Pi-2, CIO1PKT Pi-4a in the 72 ascospore progenies fit 1:1 statiscally, but there were 8 recombinant ascospore progenies in these three avirulence loci. The results suggest that Avr-Pi 1, Avr-Pi2 and Avr-Pi4a in 81 278ZB 15 are three tightly linked but independent loci. A 1 .8kb DNA fragment based on rep-PCR fingerprint (RPF1 .8) was found to link to these avirulence loci. The genetic distance between RPF1 .8 and Avr-Pil, Avr-Pi2, and Avr-Pi4a is 5.9cM, 2.2cM and 2.2cM respectively as estimated by MAPMAKER ( version 3.0). However, there are some progenies avirulent on C1O4PKT Pi-3, Co39 and some virulent on C1O5TTP-4L-23 Pi-4b even though both parents are virulent on C1O4PKT Pi-3, Co39 and avirulent on Cl O5TTP-4L-23 Pi-4b. The thesis also discusses the possible reasons which might cause the irrational recombination.
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