Validation And Primary Mapping Of QTLs For Bolting Trait In The Middle Of Chr.7 In Brassica Rapa

Brasssica rapa is an economically important crop that has been cultivated for centuries across Europe,later expanding to Central and East Asia.Premature bolting can cause large economic losses in B.rapa due to adverse effect on production and quality.Chromosome segment substitution lines?CSSLs?are ideal materials for precise mapping of quantitative trait loci?QTLs?and evaluation of gene actions or interactions in theoretical studies.The constructed CSSLs harboring possible QTLs identified in our previous studies were double checked for their phenotypes and genotypes.Primary mapping of QTLs for bolting trait in the middle of Chr.7 in B.rapa was conducted in this study.The results as follows:1.Genotype identification test were performed on six chromosome fragment substitution lines.The results showed that,three CSSLs contained only one substituted segment,and two CSSLs containing two segments and only one CSSL containing three segments derived from the donor parent'08A061'.Significant difference was observed between CSSLs and their recurrent parent,RcBr,which indicated that the selected CSSLs maybe harbored QTLs underlying genes for bolting.2.The NIL-F₂ segregating population derived from the cross between16AWD004 and RcBr.Two flanking markers,Cnu_m553a and Cnu_m044a,were used to screen recombinant in 760 individuals of NIL-F₂ population.Progeny test of the recombinants were conducted.We narrowed the candidate region down to a physical distance of 793.046 kb,between markers Nia_m030a and Cnu_m044a.3.Based on gene annotation?http://brassicadb.org/brad/index.php?,a total of two genes associated with flowering,Bra004007 and Bra003913 located in the candidate interval were detected.The Bra004007 gene has a similar function to AT1G69120 in Arabidopsis thaliana.The homeobox gene encoding the MADS domain protein that is homologous to the SRF transcription factor plays a decisive role in the transcriptional activation of AGAMOUS and can be combined with a promoter and regulated flowering time gene SVP,SOC1 and AGL24 expression.The Bra003913 gene has a similar function to BAT1G71800 gene in Arabidopsis thaliana which silenced the flower suppressor gene FLC.