| Rice blast caused by Magnaporthe oryzae(Mo)is one of the most devastating diseases of rice throughout the world.Breeding and utilizing of resistant varieties is the most economical and effective way to control this destructive disease.To better ensure successful deployment of blast resistant cultivars,it is significant to comprehend the constitution of physiological race of Mo and the resistance of rice verity in target area.Here,to make the structure of physiological race explicit in tested years,Chinese differential cultivars in recent 10 years were inoculated with strains collected in years of 2006,2011 and 2015,respectively.Simultaneously,rice cultivars in Heilongjiang province in these 3 years were also inoculated with the strains to confirm the resistant spectrum to the population and physiological race.And the avirulence gene Avr Pi12 in Mo interacting with corresponding rice resistant gene Pi12 were fine-mapped in this study.The main results are described as follows: 1.Physiological race structure of Mo in Heilongjiang provinceA set of Chinese differential cultivars were used to identify physiological race of 296 Mo isolates collected in 2006,2011 and 2015 in Heilongjiang province.The result showed that 6 groups of 12 physiological races,6 groups of 14 physiological races and 7 groups of 25 physiological races were identified in population of 2006(97 isolates),2011(103 isolates)and 2015(96 isolates),respectively.In corresponding years,the total race frequencies(f_tr)were 12.4,13.6 and 26.0;the race diversity index(h_rdi)were 0.798,0.813 and 0.947,respectively.Specific physiological races appeared in all 3 populations,and 1,4 and 13 specific physiological races were identified in 2006,2011 and 2015,respectively.There were 1,4 and 13 specific physiological races in the population of 2006,2011 and 2015,respectively,and the population-specific race frequency(f_psr)in those years were 9.1%,30.8% and 52.0%.In 2006,2011 and 2015,the total frequencies of dominant race isolate(f_tdri)were 76.0%,73.8% and 35.4%,respectively.In the past ten years in Heilongjiang province,the dominant race groups were ZD and ZE groups.ZD1 and ZE1 were dominant physiological races existing in the three populations.The composition of physiological races was related to the structure of cultivars in the area.Combined the data related to planting status of the major cultivars in these 3 years with the structural changes of physiological races in the past 10 years,the relationship between cultivars planting and physiological race structure was analyzed.It was found that the total number of major cultivars in Heilongjiang province had increased by 2.4 times,while the rice planting area had increased by 2 times.In the past 10 years,the planting structure of rice in Heilongjiang province had been greatly adjusted in cultivar and planting area;meanwhile,the analysis showed that the diversity of physiological races increased year by year,and the type and frequency of specific physiological races also increased with year.Therefore,it could be inferred that there was a positive correlation between the diversity of the race and the diversity of the variety.2.Resistance evaluation of rice cultivarsA total of 280 isolates with physiological races identified in the tested year were used to inoculate the cultivars in current years.The resistance performance of the tested cultivars was evaluated by analyzing the cultivar’s overall resistance to the tested population,the resistance to the physiological race group,the resistance to dominant physiological races,and the overall resistance to the dominant physiological race.39 rice varieties were inoculated by 97 isolates with identified physiological races in 2006(ZD and ZE groups were the dominant).There were 6 tested varieties with high overall resistance;there were 4 and 6 varieties that showed high resistance to dominant physiological race groups ZD and ZE,respectively;there were 10 varieties with high overall resistance to the 3 dominant races(ZD1,ZE1 and ZD5);there were 5,11 and 10 varieties that showed high resistance to the 3 dominant physiological races,respectively.40 rice varieties were inoculated by 87 isolates with identified physiological races in 2011(ZD and ZE groups were the dominant).There were 18 tested varieties with high overall resistance;there were 5 varieties that showed high resistance to all physiological races;there were 18 and 8 varieties that showed high resistance to dominant physiological race groups ZD and ZE,respectively;there were 20 varieties with high overall resistance to the 3 dominant races(ZD5,ZD1 and ZE1);there were 16,22 and 9 varieties that showed high resistance to the 3 dominant physiological races,respectively.24 rice varieties were inoculated by 96 isolates with identified physiological races in 2015(ZD and ZE groups were the dominant).There were 2 varieties that showed high resistance to all physiological races;the number of varieties that showed high resistance to dominant physiological race groups ZD and ZE were 10,respectively;there were 10 varieties with high overall resistance to the 3 dominant races(ZE1,ZD1 and ZD3);there were 8,8 and 11 varieties that showed high resistance to the 3 dominant physiological races,respectively.According to the statistics of the Heilongjiang Provincial Seed Administration,the major variety for rice cultivation was Kongyu 131 in Heilongjiang Province from 2006 to 2011,and it was changed to Longjing 31 as the major planting variety from 2011 to 2015,and the number of varieties also increased.It was found that the resistance of Kongyu 131 was poor.After the development of Longjing 31,it was extensively popularized as a substitute for Kongyu 131 due to its broad spectrum of resistance and stable resistance.Since 2013,there had been no reports of large-scale outbreak of rice blast in Heilongjiang.Considering the above results comprehensively,it was indicated that the rational selection and use of rice varieties in Heilongjiang province was the main factor that successfully controls the outbreak of local rice blast.3.Updating of physical map of the whole genome simple sequence repeat(SSR)markers of Mo and fine mapping of Avr Pi12 geneBased on the previous research of our laboratory,the genetic linkage map of rice blast fungus was updated to a new version.Among the original 120 SSR markers,4(MS4-6,MS4-7,MS6-15 and MS7-2)of them were abnegated;18 SSR markers were added,making 25,22,16,19,14,17 and 17 markers distributed on chromosomes 1-7 and 4 markers distributed on supercontig 8.8.Therefore,a new version of the genome-wide SSR marker physical map was constructed.Two field isolates of Mo CHL42 and CHL357 and 219 ascospore strains obtained from the hybridization of the 2 strains were used to inoculate the rice variety IRBL12-M carrying the resistance gene Pi12 and analyzed for pathogenicity.The results showed that for the phenotype of virulence and avirulence of the offspring isolates,the ratio was 1:1,indicating that the avirulence of CHL42 to the rice variety IRBL12-M was controlled by a single gene which was named Avr Pi12.Using bulked-segregant analysis(BSA)method to locate the gene rapidly,134 SSR markers were screened from the new genome SSR map of Mo.11 markers,such as SM6-1,SM6-2 and SM6-5,located on chromosome 6,were linked to the gene,and therefore Avr Pi12 was conjectured to locate on chromosome 6.To further fine-map Avr Pi12,6 markers were newly developed based on the genome sequence of 70-15 for the 2nd round of linkage analysis.Finally,this avirulence genes were located between LSM6-5 and TEL12 by newly developed 4 linkage markers LSM6-4,LSM6-6,LSM6-9 and LSM6-1.At the same time,a physical map based on the genome sequence of strain 70-15 was constructed for Avr Pi12. |
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