| Rapeseed is one of the most important oilseed crops in China, even in the world. It contributes about 40-42% of the total vegetable oil consumptions in China annually. The primary goal of breeders is developing cultivars with high productivity. Components of yield per plant include effective pods per plant, seeds per pod and seeds weight. Seeds per pod of the accessions with multilocular are more than those with bilocular. Therefore, the characteristic of multilocular would be very useful in genetic improvement and production of rapeseed along with the developments of close planting, direct-seeding, etc.Up to now, multilocular characters were only found in Brassica rapa and Brassica juncea. The result showed that multilocular character was controlled by a single recessive nuclear gene in B. rapa. Although the trait was also controlled by a single recessive nuclear gene, but modified by minor genes in B. juncea. The gene controlling multilocular was located in A genome, and easily influenced by environmental factors in B. rapa. This often made multilocular and bilocular pods appearing on a plant. The genes controlling multilocular was located in B genome, and more stable in B. juncea.In this research, we used one multilocular and three bilocular accessions of B. juncea to investigate the inheritance of multilocular characteristic and ovary paraffin section, and develop molecular markers linking to multilocular gene(s) with the application of AFLP, SCAR and SSR. The main results are as following:1. Whether direct cross or reciprocal cross made from multilocular B. juncea and bilocular B. juncea, all the F1 plants exhibited bilocular pods, and the ratios of bilocular plants (BP):multilocular plants (MP) were approximatively to 15:1 in F2 population, and BP:MP tended to 3:1 in BC1 population produced be F1 crossing multilocular B. juncea. The results indicated that the multilocular trait was controlled only by 2 recessive nuclear genes which were independent inheritance. The result indicated that the multilocular B. juncea used in this study was completely different from the materials reported before.2. It was found that the multilocular pod with four vavels and two parallelly growing pseudo-septums was developed from four carpels through the observation of ovary paraffin section. The chamber of multilocular pod was separated into three rooms (not 4 ones) by the pseudo-septums. The middle room was larger than the two lateral rooms. Unlike some ovaries developed into bicapsular on multilocular plant in B. rapa, all ovaries on a plant could develop into multilocular pods in B. juncea. 3. Though 1000-seed weight and total effective pods per plant of the multilocular individuals were less than those of the bilocular ones, but the multilocular individuals had much more seeds per pod and yield per plant than the bilocular ones had in BC1 segregating populations. This indicated that seeds per pod of the multilocular plants made the largest contribution to seed yield/plant.4. AFLP assay with BSA method was used to analyze BC1 and BC2 generations, and 9 markers linked to the Mc1/Mc2 genes were identified both in BC1 and BC2 populations. These markers distributed on both sides of the target genes. The distances between these markers and the target genes were from 6.3cM to 26.5cM. Based on comparison of the sequences between these AFLP fragments screened in a BC2 population and BAC libraries of B. rapa, SCAR and SSR primers were designed to identify the BC2, and we obtained a SSR marker SSR18 and a SCAR marker SCAR07 from the target Mc1 gene 11.5cM and 14.9cM, respectively. Using all of AFLP, SCAR and SSR markers to detect one BC1F2 population, a linkage map for the biloclus gene Mc1 in B. juncea was built.5. With the use of the obtained molecular markers of the Mc1 gene, we detected and determined the genotypes of the BC2 populations (containing the gene Mc1 or Mc2). This would be very helpful for researchers to construct large populations to fine map and clone the gene Mc1 and Mc2. |
