Breeding Of Restorer Lines 7-5,7-6 With Resistance To Sclerotinia Sclerotiorum In Brassica Napus

Brassica napus is one of the most important oil crops and high-quality protein crops in China. Both the planting area and the production occupy 1/3 of world, and main planting area locates in Yangtze River valley, occupying 1/4 of world. China is the biggest country of rapeseed in the world (Tu,2007). Sclerotinia stem rot is one of the most serious diseases of rapeseed in China, which is the main factor to influence the yield and quality of rapeseed. The incidence of the disease is from 10 percent to 80 percent and the yield loss is from 5 percent to 30 percent. Although there is some progress in disease prediction, chemical control and improvement of cultivation methods, these still havn't changed the harm of Sclerotinia stem rot to rapeseed. So It is becoming the hotspot that combining conventional breeding with modern biotechnology to breed rapeseed cultivars resisting (enduring) to Sclerotinia sclerotiorum..In this study, we use backcross breeding and molecular marker-assisted selection to improves the resistance of restorer lines 7-5,7-6(Brassica napus) to Sclerotinia sclerotiorum. L135 and Zhongshuang 9 are used as disease-resistant parent to cross with the recipient parents 7-5,7-6. F1 hybrids backcross with recurrent parent 7-5,7-6 two times. Finally, the resistant materials are selected and inbred, and the self progenies will be the new restorer lines to resist Sclerotinia sclerotiorum. The main results are as follow:1. The three F1 hybrids(7-5×L135,7-5×zhongshuang 9,7-6×L135) were backcrossed with recurrent parents 7-5,7-6 and The three BC1F1 populations (BC1F1-A, BC1F1-B, BC1F1-C) were obtained. By evaluation of the lesion length of the there BC1F1 populations by artificial inoculation of detached leaves with mycelia at the seeding stage, 71,53,80 single plants with the lesion length smaller than donor parents were derived respectively. By evaluation of the lesion length of BC1F1-A and BC1F1-B populations by artificial inoculation of haulm with mycelia at the adult stage,34,21 single plants with the lesion length smaller than donor parents were derived respectively..2. After background selection in selected plants with the lesion length smaller than donor parents at the seeding stage in the BC1F1-A, BC1F1-B, BC1F1-Cpopulations,.4,3,5 single plants with better disease-resistant and closer genetic background with recurrent parent were dervied respectively.3. The selected BC1F1 plants were backcrossed with their recurrent parents for obtaining there BC2F1 populations (BC2F1-A, BC2F1-B, BC2F1-C). After background selection with SSR markers in the there BC2F1 populations,2,2,2 single plants with closer genetic background with recurrent parent were dervied respectively from the BC2F1-A, BC2F1-B, BC2F1-C.4. The selected plants of there BC2F1 populations were inbred and three BC2F2 populations (BC2F2-A, BC2F2-B, BC2F2-C) were obtained. After evaluation of disease resistance at both the seeding and adult stages,5,4,7 single plants with better resistance were selected respectively, which could be used as the new germplasm resources of restorer lines to endure Sclerotinia sclerotiorum.5. The correlation coefficient of the results of evaluation of disease resistance at the seeding and adult stages is fairly low. But the correlation coefficient between 3d and 5d, 3d and 7d,5d and 7d at the adult stage is fairly high.