| Rice blast,caused by Magnaporthe oryzae,is one of the most dangerous fungal diseases in rice,and seriously restricted the world grain safety production.Currently,it is the most effective,economic and safety measures to control rice blast by blast resistant rice cultivars.However,the new commercial cultivars planted in a large area for 3-5 years offen became into susceptible because of pathenicity variation of M.oryzae.Therefore,the relationship between the growth rate of balst fungus isolates from the rice blast nursery in Taojiang,Hunan during 2015 and their sporulation,and the genetic diversity,pathogenicity,avirulent genes types of these isolates were studied.Meanwhile,resistant genes types of the cultivars planted in Hunan were presumped according to gene-for-gene theory.So,this research may have some significance for the breeding blast resistance and deploying resistant caltivars in Hunan.1.The mycelial growth and conidial production of 92 isolats showed that they all growed on tomato oat medium(TOM),but had different in their growth rates and sporulation,in which No.25 isolate in above 92 isolates was the maximum growth rate,9.36 mm/d and had the strongest sporulation production20.52×10~5/m L,while No.53 isolate was the minimum growth rate,4.81 mm/d;27 isolate was the weakest sporulation production,0.10×10~5/mL.The result suggested that there was no correlation between growth rate and sporulation.2.The genetic diversity of 92 isolates of M.oryzae was analyzed by 14 pairs based on SSR primers.The results shows,all of the 92 tested isolates were classified into the same genetic lineages at the 0.19 similar level;these isolates were classified into 26 genetic lineages at the 0.70 similar level,the dominant lineage XIX contains 17 isolates,18.48 of the total number of isolates.There are 23 lineages within the genealogy contains the amount Between 1 to 5 strains,from the atlas of clustering analysis separation of taojiang in Hunan disease nursery of the 92 genetic differences of rice blast fungus,genetic structure is more complex,more distant genetic relationship of individual strains.3.The avirulence genes of these 92 Magnaporthe oryzae were identified by in vitro inoculated the fifth leaves of the 24 monogenic near-isogenic lines(NILs)against blast at 5leaf stage were cultivated from LTH with known blast-resistance gene.We analyzed the interactions between the blast resistant genes by combined pathogenicity association coefficient(PAC)with resistance association coefficient(RAC).The 92 M.oryazae hold 24avirulent genes based on 24 NILs,and they also showed different level of virulence,in which the anti-stain frequency of Pi-20 was the highest with 54.35%.Moreover,results also show that the optimal combination of resistant genes was Pi-20×Pi-k~s(RAC=0.28,PAC=0.23).4.Choose 16 M.oryzae isolates with known avirulent genes of rice blast to indentify Hunan 50 rice cultivars in vitro.Analyse the virulence frequency of rice varieties against these 16 isolates based on resistance phenotype,and presume the resistance gene of rice cultivars according to“gene for gene theory”.The result shows that the virulence frequency(VF)of 50 rice cultivars are between 31.25%to 93.75%.One of them,Jianyou 8,with stronger resistance and broader resistance spectrum is recommended to use reasonably in rice production in Hunan.Clustering analysis through DPS software,these varieties are divided into 24 types at the 75%similarity coefficient,the most frequent resistance gene is Pi-20. |
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