Mapping And Breeding Application Of A Dwarf Mutant In Brassica Napus L.

Rapeseed(Brassica napus L.)is an important oilseed crop worldwide,with its oil production accounting for approximately 13% of global plant oil production.Plant height(PH)is an important structural trait that regulates lodging resistance,and harvesting index in rapeseed.Decreasing the PH of rapeseed is of great significance for improving its lodging resistance and mechanized harvesting.Currently,many dwarf genetic resources have been discovered in oilseed,but fewer have been successfully applied in varieties.Therefore,it is important to further explore the dwarfism gene resources with application potential in oilseed.In this study,we constructed a F2 population by crossing the dwarf mutant19YF123 with the tall plant material ’Zhongshuang 11’(ZS11),and the QTL-mapping relative to PH was conducted using QTL-seq.Then the linkage polymorphism molecular markers were employed to complete the PH genetic improvement of the parents of the variety ‘Huayouza 50’.The main results are as follows:1.Genetic analysis and QTL-mapping of dwarf locus.Under Gansu province environment conditions,the PH of 19YF123 was 93.5±9.8 cm,significantly lower than that of ZS11(158.4±6.2 cm),and the PH of(19YF123×ZS11)F1 hybrid was 124.7±3.4 cm.The PH of(19YF123×ZS11)F2 distributed in the range of 60 cm to 180 cm and exhibited a clear bimodal distribution.Chi-square test showed that the dwarf gene was controlled by a dominant incomplete dominant gene.DNA mixing pool sequencing of extreme individual plants in the F2 population identified a significant QTL on chromosome A10 with a peak position located at 23 Mb using QTL-seq method.Thirteen polymorphic molecular markers linked to the QTL peak position were developed,and two of them were used in the molecular breeding.2.Genetic improvement of plant height in ’Huayouza 50’ parents.Using the strategy of marker assisted selection(MAS)combined with backcross breeding,the target locus from 19YF123 was introduced into the temporary maintainer(BC59,with ZS11 genetic background)of the male sterile line RG430 A and the restorer(HF35,with Zheyou50(ZY50)genetic background)of ’Huayouza 50’.In comprehensive speed breeding(CSB)environment conditions,the PH of the heterozygous genotype plants from the BC59-BC3F1 population were 32.8±6.6 cm,which were significantly lower than those of the recurrent parent and reduced by 45.2 cm.In addition,the first branch height(FBH),length of the main inflorescence(LMI)and seed number per silique(NSS)of the heterozygous genotype plant were significantly lower than that of the recurrent parent,while there was no significant difference in the number of siliques on the whole plant(NSP),silique density of major inflorescence(MSD),and thousand seed weight(TSW)between dwarf plant and recurrent parent.The same method was used to evaluate plants from the HF35-BC4F2 and HF35-BC5F1 populations,and the PH and major agronomic traits showed similar trends with BC59-BC3F1 population.Moreover,F1 hybrids were generated by crossing the maternal parent RG430 A of ’Huayouza 50’ with a dwarf homozygous line from ZY50-BC2F2 population.The main agronomic traits of the BC59-BC3F1 population were investigated in the Wuhan field environment conditions.The PH of the dwarf plants(80.0±10.5 cm)was significantly lower than that of BC59(150.4±11.7 cm)with the FBH and LMI showed the same change than those of the recurrent parent.The BN exhibited no significantly difference between the dwarf genotype plant and the recurrent parent,while its MSD was14.6±5.9/10 cm and showed significantly higher than that of the recurrent parent(7.0±2.1/10 cm).In addition,the NSP and TSW of the dwarf plants displayed not significantly different from those of the recurrent parent.The different genotype plants from ZS11-BC2F2 population showed similar changes in PH and the major agronomic traits.In the HF35-BC4F1 population,the PH,FBH,and LMI of the dwarf plants were99.2±7.3 cm,35.1±6.8 cm,and 37.1±3.9 cm,respectively,all significantly lower than the recurrent parent(144.3±16.0 cm,76.0±10.9 cm,and 49.2±6.8 cm,respectively).The MSD and BN of the dwarf genotype were 13.0±2.2/10 cm,and 9.8±1.8,respectively,significantly higher than that of the recurrent parent(7.8±2.5/10 cm and 5.7±1.3).Additionally,the SL and NSS of the dwarf plants were not significantly different from those of the recurrent parents,while the TSW was significantly lower than that of the recurrent parents.The dwarf plants in the ZY50-BC3F2 population also show relatively similar phenotypic characteristics.3.Agronomic traits evaluation of the dwarf ’Huayouza 50’.The hybrid F1 plants(by crossing RG430 A with a dwarf homozygous plant from ZY50-BC2F2 population)were planted in the field conditions in Wuhan.The PH of the F1 plants was 98.0±10.9 cm,significantly lower than that of ’Huayouza 50’(151.3±16.8 cm),as well as the FBH and LMI.The MSD and BN of the improved hybrid F1 plants were 14.9±3.1/10 cm and 8.5±2.5,respectively,significantly higher than those of ’Huayouza 50’(7.7±1.9/10 cm and 5.7±1.3).In addition,the NSS and TSW were significantly higher than those of ’Huayouza 50’.Our study laid a solid foundation for evaluating the breeding value of the dwarf mutant19YF123 in Brassica napus L.