Genetic Diversity And Association Mapping Of Agronomic Traits For Bread Wheat Cultivars In Hebei Province, China

Plentiful genetic diversity is not only the basis for crops in raising yield gain andenhancing resistance to biotic and abiotic stresses, but also the necessities formolecular-and pyramid-breeding characterized by marker assisted selection. Hebeiprovince is one of the most important wheat-planting area in China, for its wheatcoverage and production ranking third. Though there experienced six round of wheatvariety renewal in Hebei, and not less than200cultivars had been authorized andreleased in this region since1949, the increasing of yield per unit area slows downannually. Therefore, it is necessary to systematically investigate the genetic basis ofwheat cultivars in Hebei province. From2004, we collected around170wheataccessions registered in this province, and genetically purified with agronomic traits.The objective of present study is to plant and investigate the variations of majoragronomic traits of these wheat cultivars under different environments. Furthermore,simple sequence repeat (SSR) markers were used to characterize the genetic diversityof these wheat cultivars, and to perform primarily trait-marker analysis based on themixed linear mode (MLM) using TASSEL software. The main results were asfollows:1. One hundred and sixty-nine (169) wheat accessions in Hebei province wereplanted under two different environments (Baoding Hebei, and Yangling Shaanxi),and nine major agronomic traits were investigated. The results showed that coefficientof variation of nine traits ranged from6.90to43.55, and the gene diversity indexranged from1.51to1.72. Based on Euclidean distance, all the accessions studied canbe clustered into four classes, which had their characteristic pedigree, agronomicpresence and suitable planting area. Though the wheat accessions in present studypresented genetic variation to some extent based on agronomic traits, the genetic basisof wheat accessions in Hebei was still narrow, compared to that in Henan province,Shaanxi province, Huanghuai wheat zone and the core accessions of China.2. Two hundred and thirty-one (231) microsatellite markers were used toevaluate the genetic diversity of wheat accessions in present study. The results showedthat among the A, B and D genomes of wheat, B genome presented the highestgenetic diversity, with the A genome relatively low. For the seven homoeologues,groups5and4showed the highest genetic diversity, while the genetic diversity in group7was lowest. Among the21chromosomes, genetic diversity in chromosomes4A and2D was relatively high, while genetic diversity in chromosome1A wascomparatively low. According to genetic similarity calculated from SSR data, all thewheat accessions can be clustered into five classes, which would reflect to someextent pedigree character and regional distribution character of Hebei wheataccessions in present study.3. Since1949, wheat cultivars in Hebei province have experienced six round ofwheat variety renewal. According to the renewal years, genetic diversity of the wheataccessions studied presented gradually increasing trend, though the allelic frequencyof the accessions decreased slightly. This trend was different to that of Henan,Shandong province, China landraces and core collections, and slightly different to theresults obtained in our previous study for the same set wheat accessions usingagronomic traits, seed endosperm glidians, and small number of SSR markers, whichin one hand, may be ascribed to a truly high genetic diversity of Hebei wheat cultivars,and in anther hand reflect the distinctive climatic and ecological character, andmulti-breeding units and diverse germplasm origin of Hebei wheat accessions.4. Using mixed linear mode in TASSEL package, marker-trait associationanalysis among the wheat accessions studied was carried out, and fifty-one significantassociated SSR marker loci was detected. Among them, eleven markers wereassociated with plant height, fourteen with tiller number, four with ear length, eightwith spikelet, five with number of sterile spike, nine with grain number per plant,eight with grain weight, nine with thousand-kernel weight and seven with spikeletdensity. The detected associated SSR markers in this study helps to make themarker-assisted selection, thus promoting the pyramid breeding in the not far awayfuture, and also helps to raise the breeding efficacy in Hebei province.