Genetic Improvement Of Thousand Seed Weight Of The Brassica Napus Core Parent 7-5

Increasing the total production of rapeseed is the main approach to ensure the supply of edible vegetable oil in China, because the rapeseed oil is one of the main edible vegetable oil in China. However, the planting area for rapeseed is shrinking in recent years. So the most effective measure to increase the output is to further increase the yield per unit area, which is mostly determined by the yield per plant and the planting density. It has been a mainstream strategy in rapeseed breeding to improve the yield per plant by raising and coordinating the three yield components, the thousand seed weight（TSW）, the seeds per silique（SS）, and the siliques per plant（SP）.The Brassica napus restorer 7-5, which was developed by our lab, has been widely used in generating multiple hybrid cultivars with high yield and superior quality. However, all the progenies of 7-5 presented relatively low TSW. It was promising that the increase on TSW of 7-5 will result in higher TSW progenies, which leads to the yield further improvement of its hybrids.In this study, the breeding material ZX11 X with high TSW which was selected by our lab in the selfing progenies of semi-winter Brassica napus general cultivar ZS11, was utilized as donor parent to improve the TSW of 7-5, the recurrent parent, through conventional phenotypic selection combined with molecular marker assisted genetic background selection. The main results were as follows:1. Segregation populations for the size of seed of BC₄F₂ generation were generated through four times of backcrossing, and phenotypic selection on TSW along with background selections in BC₁F₁, BC₂F₁ and BC₃F₁ progenies. Finally, two BC₄F₂ populations showed 3:1 segregation ratio of high-TSW: low-TSW.2. A total of four TSW SSR markers（SSR1313, SSR1316, SSR1328 and SSR1820） linked to a TSW QTL were obtained by using TSW extreme plants of BC₄F₂ populations through the bulked segregation analysis（BSA） method. These four SSR markers were confirmed to have favorable microsynteny with A9 chromosome according to BLAST of Brassica database. Besides, the markers SSR1313 and SSR1316 located on A9 chromosome of Brassica napus structured by our lab. Therefore, we concluded that the TSW segregation of BC₄F₂ populations was probably controlled by a major QTL on A9 chromosome.3. The genetic background recovery rate of three BC₄F₅ lines and five BC₃F₆ lines was evaluated by RAD-seq technology. The background recovery rate of all BC₄F₅ lines and two BC₃F₆ lines were over 80%, and that of three BC₃F₆ lines were over 60%. Besides, the foreground selection markers were located in the no recovery regions. These eight lines were comprehensively evaluated for the genetic background recovery and their yield related traits including thousand seed weight（TSW）, seeds per silique（SS）, seed density（SD）, silique length（SL）, and four of which with higher TSW, highly recovered genetic background compared to 7-5, and moderate SS, SD and SL traits between two parents, were obtained.4. About 700 regenerated plantlets were obtained by microspore culture for BC₄F₅ and BC₃F₆ lines. These plantlets were potential near-isogenic lines（NIL） for QTL fine mapping of TSW, as well as excellent breeding material for TSW improvement.