Screening For Midge-resistance Wheat Germplasm And Their Linked DNA-based Molecular Markers

Wheat midge is one of the economically important pest insects that negatively affect wheat grain yield and quality.In China,two midge species,i.e.Sitodiplosis mosellana Gehin and Contarinia tritici Kirby,with S.mosellana as the most prevalent species.It is documented that application of pesticide and midge-resistant wheat varieties are two main measures to control or lower such yiled losses incurred by midge.However,chemical control is difficult to apply at due date and has the risk of environment pollution.At present,screening and applying of midge-resistant wheat varieties has been proved a right way considering both environment risk and farmer’s cost.In this study,280 recombinant inbred lines（Recombinant Inbred Lines,RIL）obtained from the hybrid"Jimai 24"（midge resistant wheat variety）and"6218"（midge-sensitive wheat line）hybrids were used as the materials.QTL conferring resistance to wheat midge was studied by SSR（EST）and SNP markers.The main results are as follows:1.By evaluating the wheat midge resistance of 128 wheat species,a total of 27 wheat varieties shows resistant to midge,including immune varieties of Handan 9 and Qinong741,highly resistant varieties of 25 wheat varieties.Based on pedigree analysis,these midge resistant wheat have their origin from Lumai 13 or Lumai series,Jimai 24 series or Xiaoyan series.2.280 RIL population made by high-resitance to wheat midge cultivar Jimai 24 crossed with susceptible wheat cultivar 6218.The resistance index of Jimai 24 was 0.10 and the wheat species 6218 was 3.02.The resistance to wheat midge of 280 RIL lines were assessed and divided to 44 high-resistance lines,65 medium-resistance lines,63 low-resistance lines,48 susceptible lines and 60 high-sensitivity lines.The 44high-resistance lines could be used to wheat midge resistance breeding.3.Different linkage maps,ie.SSR（or EST）-based,SNP-based or SNP+SSR（EST）based,were constructed using 280 recombinant inbred lines（F₇）of 6218 with Jimai 24.Among the three genetic maps,SNP+SSR（EST）genetic map was the longest,with a total length of 7590.36 cM,and the average genetic distance between any two markers was 6.09cM.4.Two QTL related to midge-resistance were detected on chromosomes 2D and 4A using DNA-based molecular markers.The SNP marker closely linked with the major QTL on chromosomes 4A are located between AX-108942696 and AX-108942696.The genetic distance between two SNP markers is 0.54 cM with LOD value of 14.46,which can explain 29.14%of the phenotypic variation.These markers could be converted to KASP markers and could be used to identify resistance for wheat midge in wheat lines.