Wheat Blossom Midge(sitodiplosis Mosellana Géhin) Resistance Screening And Association Analysis Of 137 Wheat Cultivars In Northern China

Wheat blossom midge(Sitodiplosis mosellana Géhin) is one of the most economically important pests for bread wheat(Tricitumaestivum L.) production in northern China and other countries(such as countries in North America). Breeding and application of resistant wheat cultivars has been documented as an economic, safe and effective way to control midge damage and to reduce the resultant wheat losses. However, for the frequent migration of midge and the subsequent poor pest resistance screening in the field, breeding for wheat cultivars with midge resistance progresses slowly. Fortunately, advances in gene-mapping or QTL analysis for agronomic traits in major crops including wheat supply such a way to improve midge resistance selection efficiency in term of marker-assisted selection(MAS). There have successful reports on wheat breeding of midge resistance in Canada by using MAS technique,while such research is scarcein China.Association mapping based on linkage disequilibrium(LD) with natural population as materials has made many successes in deciding trait-marker relationship and discovering desirable alleles. Therefore, the objectives of present study are: 1) to screen wheat germplasm resistant to midge on the pest nursery artificially constructed, and 2) to discovery allelic variation for midge resistance in 137 wheat cultivars released in North China in recent ten years. The major results acquired are as follows.1.One hundred and thirty-seven(137) bread wheat accessions in north China are screened for their midge resistance in the pest nursery artificially constructed. Resistance among accessions differs obviously. In 2013, 34 cultivars show high resistance, 29 medium resistance, 25 low resistance,17 infect, 32 high infect of 137 wheat accessions.In 2014, 42 cultivars show high resistance, 33 medium resistance, 29 low resistance, 12 infect, 21 high infect of 137 wheat accessions.2. Two hundred and seventy-three(273)polymorphic microsatellite(SSR) primer sets were used to analyze the genetic diversity of the same set(137) wheat accessions. A total of 963 allelic variations were detected,with B genome having the highest genetic diversity, and A genome the lowest diversity. The average number of alleles per SSR locus was 3.56,ranging from 2 to 9. Among the seven groups of wheat chromosomes,thehomoeologous groups of 4 and 7showed higher genetic diversity, while the homoeologous group 5showed the lowest diversity.Ofthe 21 chromosomes of the accessions analyzed,genetic diversity on chromosomes 4A and 4D was much higher, whereas genetic diversity on chromosomes 5D and 1D was relatively lower.As for midge resistance, accessions conferring high tomedium resistance showed relatively higher genetic diversity.3. Before association mapping, population structure and linkage disequilibrium(LD) of the wheat accession panel were determinedwith the polymorphic SSR data. The wheat panel can be divided into five subgroups, with 11.4% accessions being divided into subgroup with mixed origins. The background LD value for the association panel was 0.0467(r2=0.0467). Based on this value, LD decay for the association panel was determinedas 25.8 c M.4. Based on mixed-linear mode in TASSEL 3.0 package, trait-marker associations were undergone for the 273 polymorphic SSR markers and midge resistance. Five SSR loci with significant effects were detected in 2013, six SSR loci with significant effects were detected in 2014. These associated SSR loci were of great importancefor the further mapping of midge resistance and marker-assisted selection for midge resistance selection in future wheat breeding.