| Tobacco black shank is an egg fungus disease caused by Phytophthora paradisiaca var.nicotianae,which destroys the yield and quality of tobacco and is one of the most serious diseases in tobacco production.It is a very economic and effective method to control tobacco black shank by using molecular breeding to obtain genetic resistance without affecting yield and quality.It is an important theoretical basis for this aim to explore and locate the resistance genes of black shank disease and develop the resistance function markers.In recent years,the multi-parent advanced generation inter-cross population has shown strong advantages in many plant genetic studies,but its utilization in tobacco is rarely reported.In this study,we constructed a set of 8-parent cross MAGIC population in tobacco.On this basis,we used high-density SNP chip to detect the genotypes of 8 parents and 600 MAGIC populations,and analyzed the genetic diversity among different materials.Then,we used genome-wide association analysis to detect QTLs related to the resistance of tobacco black shank in seedling and field stage,so as to find out those related to the resistance of black shank Candidate genes,mining favorable alleles,in order to provide support for tobacco breeding and germplasm innovation.The main results are as follows:?1?On the basis of previous work,the construction of tobacco MAGIC population was completed.The population was constructed with 8 different tobacco Germplasms?including cigar,oriental tobacco,burley tobacco,sun cured tobacco and flue-cured tobacco?as parents,including 600 lines of homozygous progeny?2?8 parents and MAGIC population were detected and genotyped by 430K tobacco SNP chip.After deleting the markers with no polymorphism between parents,deletion rate more than 10%,rare allele variation rate less than 5%,124151 high-quality SNP markers were obtained.These markers can cover 24 chromosomes of tobacco evenly,covering 2933.4 Mb of the whole tobacco genome,and the average physical distance between SNP markers is only 25.77Kb.?3?Using 124151 polymorphic SNP markers to analyze the principal component and genetic relationship of the population,it was found that there was no obvious population structure in magic population.?4?The phenotypes of black shank in magic population at seedling stage and field stage were statistically analyzed.There were significant differences in resistance to black shank among different lines.?5?Using TASSEL V5.2.40 software mixed linear model?MLM,PCA+K?,the correlation between black shank disease index and incidence rate of seedling and field stage was analyzed.Under the condition of P<5×10-7,28 QTLs significantly related to tobacco black shank resistance were detected,and 13 QTLs were stably detected in seedling and field stage.Five major QTLs were identified according to the criterion of effect value greater than 10%,which were qHb7,qHb9.1,qHb9.2,qHb9.3,qHb12.1.?6?According to the different base types of qHb7,qHb9.1,qHb9.2,qHb9.3 and qHb12.1 peak SNP,600 magic populations were divided into different groups,and it was found that some base types always appeared together.Therefore,qHb7,qHb9.1,qHb9.2,qHb9.3 and qHb12.1 may belong to the same QTL.?7?The resistance and agronomic characters of two groups of lines based on qHb9.3 and qHb12.1were compared.It was found that the introduction of major QTLs had no significant effect on tobacco agronomic characters.?8?94 resistant materials were selected from 600 MAGIC populations,and 4 resistant materials of flue-cured tobacco type were preliminarily selected according to their field performance. |
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