Identification Of Physiological Races Of Magnaporthe Oryzae From Rice Blast Nursery In Taojiang And Evaluation Of Blast Resistance Of Improved Lines With Different Resistance Genes

Rice is the most important food crop in China and rice blast is the most devastating disease in rice production.Breeding and utilization of resistant varieties is the most economical and effective measure to control rice blast.The identification and evaluation is the basis for rice blast resistance breeding and rational utilization of research.So far,natural induction is still the most effective,reliable and economical method for identification and evaluation of blast resistance in nurseries with high selection pressure and rich genetic composition of the pathogen population.Diseased nursery in Taojiang of Hunan province is the identification point for rice blast resistance in the regional trials of new rice varieties in Middle and Lower Yangtze River in China and Hunan Province.Only the rice varieties identified by the disease nursery can pass the national or provincial examination and be popularized and planted in the rice regions in the middle and lower reaches of the Yangtze River and Hunan Province in China.To clarify the composition of physiological race and types of dominant race as well as the utilization value of rice blast resistance genes were of great significance for scientific guidance of the breeding and rational utilization of rice blast resistant varieties in Hunan Province and the whole country.Therefore,in this study,the composition of physiological race of Magnaporthe oryzae in Taojiang diseased nursery was studied,and the resistance levels of the varieties containing different resistance genes were evaluated.Results were showed as follows:1.The ability of conidia production of 64 M.oryzae isolates was analyzed that were isolated from the rice blast nursery in Taojiang of Hunan province,in 2018.The result showed that continuous irradiation with blue and black light and together with the oat tomato agar medium could effectively induce these isolates to produce conidia.However,there were significant differences in the ability of conidia production among different strains.Physiological race identification and virulence analysis were performed using 7 rice varieties used for physiological race identification.Results showed that the 53 tested isolates were divided into 4 groups and 12 physiological races.The ZB was the dominant population,and the ZB₁₅was the dominant physiological race.The highly virulent physiological race ZB₁appeared more frequently.Besides,the most virulent physiological race ZA₁also appeared.In conclusion,the population composition of M.oryzae isolates from Taojiang disease nursery was abundant,and the disease-resistant varieties or resources,which were identified and screened out in Taojiang disease nursery,will play an important guiding role in rice production and resistance breeding in Hunan Province and even the Middle and Lower Yangtze River.2.The resistance of the rice varieties containing different resistance genes lines was identified.Results showed that the resisitance level of the improved lines was significantly improved when compared to their original parent lines.In terms of single gene lines,the resistance level of Pi54 gene-containing lines is relatively poor,the Pi2 gene-containing lines have the highest resistance level,followed by the Pi9 gene-containing lines,and most of the lines containing Pita single-gene lines also had better resistance level.Among the dual-gene lines,the lines harboring Pi54 and Pita genes showed moderate resistance,with the exception of one line that showed moderately susceptible;the lines containing Pi2 and Pita all showed moderate resistance,and the disease grade of panicle blast incidence was 5,the resistance composite index was below 3.5.This revealed that the Pi2 gene,or pyramiding of two or more genes of Pi54、Pita、Pi9、Pi2,were recommended for widely use in Hunan Province or the Middle and Lower Yangtze River.