Breeding New Boron-efficient Accessions By Molecular Marker-assisted Selection In Brassica Napus L.

Rapeseed is the second largest oil crop in China.It is sensitive to the mineral elements—boron,and it is one of the crops with the highest boron content.The Yangtze River Basin,which is the main rapeseed planting area in China,has experienced a large area of boron deficiency caused by“flowers without seeds”phenomenon.So far,Chinese farmers still apply boron fertilizer to guarantee the production of rapeseed.However,boron is still the least deficient and toxic concentration in the range of the 17essential nutrients.It is deficient when the content of hot water-soluble boron（HWSB）is less than 0.5mg/kg,and it is toxic when the content of boron is higher than 1mg/kg.Therefore,in order to better solve the impact of soil boron deficiency on production,it is of important practical value to breed rapeseed varieties that can efficiently use boron.In this study,2016-XFSB was used as the donor parent,and Brassica napus L.inbred lines 4270,8759,L-135R,and 621R were used as recurrent parents.Using molecular marker-assisted selection technology,we hope to breed new Boron-efficient accessions with the genetic background of the recurrent parents 4270,8759,L-135R and 621R.The main results are summarized as follows:1.The 2016-XFSB,which is the boron efficient variety,is used as the donor parent to backcross the reincarnation parent respectively.The BC₃F₃ generation of the combination 4270×2016-XFSB and 8759×2016-XFSB and BC₅F₃ generation of the combination L-135R×2016-XFSB and 621R×2016-XFSB were developed. Through molecular marker-assisted selection,the elite allele at the target locus Bna A03.NIP5;1 was successfully introduced into the recurrent parents,and some homozygous lines with efficient boron utilization was obtained.Their background recovery rates are 82.6%,80.2%,92.2%,and 98.3%.2.hydroponic experiment and inductively coupled plasma mass spectrometer was used to measure the boron utilization efficiency of the improved accessions and the original parent.The results showed that the boron absorption and utilization efficiency of the genetic improved accessions of 4270,L-135R,and 621R were all significantly improved,and their plant growth was also enhanced under low boron stress.It can also show obvious growth advantages under normal boron concentration environment.The introduction of elite allele of Bna A03.NIP5;1 into 8759 can significantly increase the dry matter accumulation of its roots,but the boron content of the whole plant does not change significantly.3.Field comparison experiments were conducted between the improved accessions and their parents in soils with three boron concentrations（Wuhan,Jiangling, Wuxue）,and the results showed that introducing elite allele of the Bna A03.NIP5;1 into 4270,L-135R and 621R can significantly improve their absorption.The improved accessions have significantly reduced the frequency of boron deficiency extent under the low boron concentration and has obvious growth advantages under normal boron concentration.Compared with the parent,the accessions with the Bna A03.NIP5;1 gene have significantly earlier flowering time,higer plant height, longer silique length,more seed number per silique,and heavier 1000-grain weight gain.But introducing elite allele of the Bna A03.NIP5;1 into 8759 can’t improve its’boron absorption,and even has some negative impact.