Genetic Dissection Of Important Agronomic Traits In Brassica Rapa

Brassica rapa (syn. campestris) is an important species of the Brassica genus, which includes a variety of vegetable and oilseed crops. Complex genetic basis of this crop make it difficult to improve some important agronomic traits. A vast of results indicated that only few systematic researches on genetic diversity of B. rapa were reported because of limited accessions and a limited number of markers. It is necessary to exploit existing genetic variation to dissect some agronomic and nutritional quality traits in B. rapa at molecular levels and this will be used for exploitation and utilization to key genes in B. rapa.In the present study, Fluorescent AFLP technology was employed to assess the genetic diversity and the relatonship among phenotypic variation, geographic origin and polymorphism at DNA level amongst a large collection of Brassica rapa accessions derived from different countries. And we described natural variation for phytate and free phophorus contents detected with HPLC method in B. rapa leaves and seeds. It would be useful to unravel phytate and free phophorus accumulation and genetics in B. rapa. Based on the selection of optimal parents, genetic research segeragation populations with abundant information were constructed and genetic linkage maps of B. rapa were developed. Furthormore, quantitative trait loci (QTL) analysis of some important agronomic traits has been performed. Main conclusions are listed as follows:1. The level of polymorphism was very high and the degree of polymorphism was more than 80%. Cluster analysis was performed using the un-weighted pair group method with arithmetic averages (UPGMA) and a dendogram was established using the AFLP fingerprints. The result indicated the B. rapa accessions were arranged into two main sets (cluster I , and cluster II) according to the origin of the accessions. The cluster analysis revealed groups, often with low bootstrap values, which coincide with cultivar groups. The low bootstrap values for many of the groups showed that most polymorphisms do not contribute to the phenotypic variation, suggesting that the amount of genetic variation present within the groups was often comparable to the variation between the different sub-groups and only a few genes were involved in causing the extreme morphologies. Most interesting information revealed by the phenetic tree is that different morphotypes are often more related to other morphotypes from the same region (East Asia versus Europe) than similar morphotypes from different regions, suggesting either independent origin in both regions or a long and separate domestication and breeding history in both regions.2. Natural variation has been shown to be present in accessions of B. rapa for phytate and free phosphorus levels in leaves and seeds. Variation in phytate and free phosphorus levels in leaves was about 10-fold. Variation in seeds was lower, around two or three fold. The levels of phytate in seeds were higher than that in leaves, while the free phosphorus levels in leaves were higher than that in seeds. A positive correlation between the two components was detected. And the variation...