Genetic Diversity And Mating Type Distribution Of Setosphaeria Turcica In China

In recent years, with the replacement of maize varieties, the changement of cultivation pattern and unpleasant climate change, the occurrence of Northern leaf blight of corn was more and more seriously in our country and the maize production was threatened obvionsly. Therefore, the dynamic changes of race and genetic variation of Setosphaeria turcica were monitored for years, which was significant for understanding the development trend of the disease, illuserating succession race of pathogens, and exploring the effective disease control methods. In the study, 522 strains were isolated from disease samples, which were collected from Donghua North spring corn region, Huanghuaihai Summer corn region, Northwest corn region and Southwest mountainous corn region from 2011 to 2014. The mating types and genetic diversity of 522 strains were detected at the molecular level using ISSR fingerprinting technology. The results preliminarily cleared that the relationship between the genetic diversity of S. turcica and geographical origin years and mating type. The research results provided evidence for selecting and distributing of resistant varieties, analyzing the interaction between varieties and pathogens. The main research results were as follows:1. In the greenhouse, the physiological race of 19 isolates of S. turcica were identified using differential hosts. The results showed that there were nine races. One strain was race 0, which occupied 5.26%; one strain was race 2, which occupied 5.26%; four strains were race N, which occupied 21.05%; one strain was race 12, which occupied 5.26%; one strain was race 13, which occupied 5.26%; five strains were race 1N, which occupied 26.32%; three strains were race 12 N, which occupied 15.80%; two strains were race 13 N, which occupied 10.53%.2. The results of molecular identification on the mating type of 522 strains showed that 95 isolates were “a” mating type, which occupied 90.47% of all the 2011 identified strains; 5 isolates were “A” mating type, which were 4.76%; 4 isolates were “Aa”, which were 3.81%. 1 isolate was neutral strain, which was 0.96%. In the identified strains of 2012, 99 isolates were “a” mating type, which were 93.4%. None of the strains was “A” mating type; 5 isolates were “Aa”, which were 4.71%. 2 isolates were neutral strain, which were 1.89%. In the identified strains of 2013, 147 isolates were “a” mating type, which occupied 87.5% of the 2013 identified strains; 14 isolates were “A” mating type, which were 8.33%; 5 isolates were “Aa”, which were 2.98%. 2 isolates were neutral strain, which were 1.19% of the total identified strains. In the identified strains of 2014, 121 isolates were “a” mating type, which occupied 84.61%; 11 isolates were “A” mating type, which were occupied 7.69%; 3 isolates were “Aa”, which were 2.10%. 8 isolates were neutral strain, which were 5.60%. “a” mating type taken a large proportion on the mating type during 2011-2014, which was agreement with the distribution ratio and the annual.3. 186 DNA fragments were amplified using 18 ISSR primers and average primer has 10.33 bands. 175 polymorphic loci were found in 522 isolates, which were 94.1% of DNA fragments. The strip number of primers amplified from 8 to 16 bands, polymorphism lowest percentage was 77.8% and the highest was 100%. The results indicated that there was huge difference among S. turcica and displayed significant genetic diversity among pathgens.4. Based on the amplification results and the genetic similarity analysis by NTSYS-pc software, the cluster analysing showed that the strains from the same year and different regions displayed similarer than the strains from the different regions. It illustrated that the genetic differentiation was similar among the strains from the same region. The strains from the same region and different years showed the annual variation. The results described that the S. turcica from the China corn production areas displayed significant genetic diversity from 2011 to 2014, and it had relationships with the geographical position and years, but had not relationship with mating type.