Genetic Analysis And Mapping Of QTLs For Resistance To Two Species Of Cereal Cyst Nematode In Wheat Cultivars

Wheat (Triticum aestivum L.) is a major food crop for human survival.The cereal cyst nematodes (CCN) are recognized as one of plant-parasitic nematodeson cereals. Recently, Two species of cereal cyst nematodes, Heterodera avenae and H.filipjevi, have been reported to be a serious threat to the food security andsignificantly reduce wheat yield in our country. Given both economically as well asfor environmental reasons, the effective and economy method to avoid crop damage isto develop resistant gene or germplasm, breed and plant resistant or tolerant cultivarsto CCN. Accordingly, it is greatly significant in discover the genetic basis of CCN forthe selection and rational application of cultivars. Fast development of the quantitativegenetics and the molecular biology has provided an available approach to study thegenetic mechanism and genetic patterns in wheat. In addition, it is very important inconstructing the genetic linkage map, mapping QTLs for CCN of wheat. These resultswill show critical significance of theory and practice in wheat research for moleculargenetic improvement in the future.The objectives of this research were to analyze the inheritance of resistance to H.avenae from Zhengzhou and H. filipjevi from Xuchang of F2populations derivedfrom the crosses Wenmai19×Zhongyu6and Wenmai19×Taikong6. The methodof joint segregation analysis of single generation of major gene plus polygene mixedinheritance model was used to analyze the inheritance of resistance in Taikong6andZhongyu6. A genetic linkage map for target chromosomes constructed using SSRmarkers and QTL (quantitative trait loci) mapping analysis about the resistance ofTaikong6to H. avenae was performed by QTL Icimapping v3.2which based aninclusive composite internal mapping. The detailed results were available as follows:(1) Based on the results of inoculation test and field test, we found that theresistance of common wheat cultivar Taikong6to H. avenae (Xingyang population)and H. filipjevi (Xuchang population), and that of Zhongyu6to H. avenae (Xingyangpopulation) and H. filipjevi (Bo’ai population) appeared to be quantitative inheritance. (2) The resistance of Taikong6to H. avenae (Xingyang population) and toH. filipjevi (Xuchang population) was controlled by two major genes. The optimalmodel for inoculation test fitted B-3(two additive major genes model) and theheritability of two major genes was60.76%. The resistance to H. avenae in diseasefield of Xingyang was controlled by two major genes with additive-dominance effects(B-2), and the heritability was91.45%. Among the two major genes, the first showedcompletely negative dominance, while the second expressed negative partialdominanc. The resistance to H. filipjevi (Xuchang population) which was according toB-2model, and the two major genes displayed completely negative dominance withthe heritability of84.82%. Furthermore, the addictive effect in each environment waspositive and the first pair of two major genes played an important role in theresistance to H. avenae or H. filipjevi.(3) The resistance of Zhongyu6to H. filipjevi (Bo’ai population) and H. avenae(Xingyang population) in the case of inoculation was controlled by one major genewith the heritability of38.12%and59.35%, respectively. Both additive and dominantgenetic effects controlled the resistance to H. avenae (Xingyang population), amongwhich, the addictive effect was main in gene effect with negative partial dominance.While the two major genes resistant to H. filipjevi (Bo’ai population) displayedcompletely negative dominance.(4) Total of160pairs SSR markers were available with showing SSRpolymorphism differences between two parents of F2from795pairs SSR originallyselected. The polymorphism frequency was20.13%. Total of31SSR markers from40pairs SSR markers were mapped on6linkage groups using the MAP in QTLIciMapping v3.2and the average number of SSR makers per every linkage groupranged from2to11. The linkage genetic map was covered603.28cM and the averageinterval between two SSR markers was19.46cM on the linkage map.(5) Total of6additive QTLs were identified for controlling H. avenae of Taikong6making the use of BIP in QTL IciMapping v3.2. Among which, there were3QTLsin the first linkage group which were mapped on chromosome6B; and there was1QTL in the second linkage group mapped on chromosome1B; the last two QTLswere discovered in the6thlinkage group mapped on chromosome2B. These QTLscould explain phenotypic variation ranged from2.1917%to16.41391%, amongwhich，Qccn.wt-2B-1was regulated by major gene, and the others were regulated byminor-effect polygenes. Furthermore, all the six QTLs could increase the resistance to H. avenae in Taikong6.