Mapping Of QTLs Conferring Resistance To Northern Corn Leaf Blight By Applying Four Linkage Populations

Maize is an important crop which was used as food,forageand deep-processing raw materials worldwide.It played an important role in agricultural production.In maize production,the occurrence of pests and diseases was the major factor that affected the yield and quality of maize.Among them,Northern corn leaf blight(NCLB)was one of the most important diseases in main maize producing areas of in China.In recent years,Northern corn leaf blight has been increasing year by year on account of climate change and the evolution of pathogen races.It brought enormous damage to the planting of maize.It is an effective method to select and breed resistant to varieties of Northern corn leaf blight.Genetic study on resistance to NCLB could provide theoretical guidance for variety breeding.In study,four inbred lines were used as resistant parent and susceptible parental inbred line GEMS41 as recurrent parent.Totally four linkage populations was constructed and used for gene mapping.The results are as following:1.In 2016 and 2017,resistance to NCLB of each line of these four populations and their parents was planted in maize production area at Jilin province and Heilongjiang province in northern China where the disease of NCLB occurred frequently including Lishu,Yushu and Shuangcheng.Four populations were named as Population 1 :(DAN598×GEMS41)×GEMS41 BC2F5 including 79 families;Population 2:(P178×GEMS41)×GEMS41 BC2F4 for 108 families.Population 3:(TY1×GEMS41)×GEMS41 BC1F4 for 163 families;Population 4:(CML496×GEMS41)×GEMS41 BC2F5 with 80 families in number.In the period of maize last milk stage,we investigated the score of NCLB by the grading standards ranging at 1-9.The phenotypic evaluaton showed that there was a significant difference in disease resistance between four donor parents(DAN598,P178,TY1 and CML496)and recurrent parent GEMS41.The parental inbred line GEMS41 were highly susceptible scored at about 7,and other 4 parents were highly resistant scored at about 1.The families of four populations also existed widely variation in resistance of NCLB and laid the foundation for resistant QTL mapping.2.A number of 852 KASP markers were applied for the genotyping of four populations.Polymorphic markers were screened out among five parental inbred lines and their populations which were used for constructing molecular marker linkage maps.Four populations constructed four linkage maps with 344,349,345,324 polymorphic SNP markers respectively.These maps covered 1744.88 c M,2336.16 c M,1376.56 c M and 2067.59 c M in maize genome with an average interval of 5.07 c M,6.69 c M,3.99 c M and 6.38 c M in turn.3.Inclusive Composite Interval Mapping method(ICIM)was adopted for QTL mapping.A total of 20 QTLs that showed resistance to NCLB were located in different environments among four populations.These QTLs contained 8 QTLs whose phenotypic variation explanation(PVE)were more than 10% that could be considered to be major QTL.We named them as q NCLB1.05,q NCLB1.07,q NCLB1.09,q NCLB2.09,q NCLB4.07,q NCLB8.02,q NCLB8.06 and q NCLB9.03 according to the distribution of QTL on the chromosome.Among these QTLs,3 major QTLs(q NCLB1.05,q NCLB1.09 and q NCLB8.06)were detected in population 1;Population 2 detected 4 major QTLs(q NCLB2.09,q NCLB8.02,q NCLB8.06 and q NCLB9.03);Population 3 and population 4 both detected 1 major QTL(q NCLB1.07 and q NCLB4.07).The resistance of the 8 major QTL was all from their donor parents.Comparing with the former research,it was found that q NCLB8.06 was located in the region where the gene Ht2 and Htn1 were located.q NCLB1.05,q NCLB1.07 and q NCLB1.09 were located in different region from the formers and could be new major QTL.q NCLB2.09 was tested in two environments and its PVE>10%.It might be a QTL that can be stably inherited and less affected by the environment.q NCLB4.07,q NCLB8.02 and q NCLB9.03 were not reported and could be new major QTL.In summary,according to these results,it paves the way for the fine mapping of NCLB.Moreover,these QTLs could be a desirable target for marker-assisted selection for NCLB resistance in maize breeding programs.