| Rice blast,caused by Magnaporthe oryzae,is one of the most serious diseases of rice.At present,breeding and planting resistant cultivars is the most effective and economical method to control rice blast.However,resistant cultivars will lose resistance because of the diversity and highly variation in M oryzae isolates in 3 to 5 years.The interaction between rice and M.following the "gene-for-gene hypothesis"shows the durability of resistant cultivars is closely linked with avirulence gene of M.oryzae.Therefore,it is of great practical significance to study avirulence gene of M.oryzae and deduce resistance genotypes in main rice cultivars on the promotion and distribution of resistant cultivars in Fujian Province.In my study,a total of 236 single spore isolates,collected from different growing regions of Fujian Province in 2006 to 2015,were used to detect the Avr genes by the specific primers of A VR-Pik?A VR-Pital?AVR-Pita2?AVR-Pita3?PWL2?AVRI-C039?ACE1?AVR-Piz-t?AVR-Pia?A VR-Pii?A VR-Pikm.The results showed the main mutant type of Avr genes in M oryzae isolates from Fujian Province was deletion.Among the 11 types of Avr genes,A VR-Pik was at the highest frequency each year,ranging from 91.67%to 100%,which showed most isolates carried AVR-Pik and therefore was able to overcome the differential cultivars carrying Pik.The frequency of AVR-Pita3?AVR-Piz-t?PWL2 were all above 66.67%.On the other hand,tht AVR1-C039 and AVR-Pii loci of all isolates were missing.Pathogenicity of 60 M oryzae isolates against 24 rice cultivars with Pi-gene were assayed by artificial inoculation.The results showed that pathogenicity of 60 isolates against 24 rice cultivars with Pi-gene differed significantly,ranging from 8.33%to 91.67%.The occurrence frequency of strong pathogenic strains and stronger pathogenic strains was 58.83%and 28.33%,respectively,which indicated 60 M.oryzae isolates had strong virulence against Pi-gene.Frequencies of all virulence differed significantly among the 60 isolates,ranging from 10.00%-93.33%.The virulence frequency of 60 isolates to Pik and Pikm was at the loweat,with the value of 10.00%and 13.33%,respectively.However,the virulence frequency of 60 isolates to Pi-a(1)and Pi-t was at the highest,with the value of 93.33%.The virulence frequency of 60 isolates to 10 Pi-gene,for example Pi-sh,Pi-11,Pii,ranged from 76.67%to 91.67%.These results revealed that the resistant genes corresponding to these avirulent genes had already lost resistance against rice blast and combined with other Pi-gene in Fujian Province.The resistant genotypes of the 25 main rice cultivars from Fujian were identified by 60 M.oryzae isolates known avirulent genes.The virulence frequency of 60 isolates to Guyou 1186,Chunyou 84,Guyou 2329 and other 15 main rice cultivars were all below 20%,accounting for 72.00%of the total,which suggested these rice varieties could be planted in the field of Fujian Province.Further analysis indicated gufeng A,quanfeng A,and taifeng A could be used as resistant breeding parents in Fujian Province.The virulence frequency of 60 isolates to zhongyou2155,jinnongyou3you3,yiyou 115 and ? youhang2 ranged from 20.00%to 50.00%,accounting for 16.00%of the total.The virulence frequency of 60 isolates to liangyou616,guangliangyou676 and liangyou667 ranged from 50.00%to 76.77%,indicating female parent guangzhan63-4s should be hybridized with the male parent with better resistance in rice breeding in Fujian Province. |
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