Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2007
Publication Date: 2/27/2007
Citation: Szalma, S.J., Hostert, B., Ledeaux, J., Stuber, C.W., Holland, J.B. 2007. Qtl mapping with near-isogenic lines in maize. Theoretical and Applied Genetics. 114:1211-1228. Interpretive Summary: We developed a new approach to mapping genes affecting complex traits like flowering time and yield in plants. The approach, called near-isogenic line mapping, involves creating a set of lines that are genetically very similar (about 95% identical), but differ for which gene regions have been introduced from a “donor” parent line. This allows testing of the effects of the different gene regions from the donor parent by comparing each near-isogenic line to the control line, which has no donor parent genes. We created a set of 89 such lines of corn (maize) and characterized them with genetic markers to show which gene regions from the donor parent are carried in each NIL. Then we grew the lines in field experiments to demonstrate their utility in identify the effects of each of these regions on flowering time in corn.
Technical Abstract: A set of 89 near-isogenic lines (NILs) of maize was created using marker-assisted selection. Nineteen genomic regions, identified by restriction fragment length polymorphism loci and chosen to represent portions of all 10 maize chromosomes, were introgressed by backcrossing three generations from donor line Tx303 into the B73 genetic background. NILs were genotyped at an additional 128 simple sequence repeat loci to estimate the size of introgressions and the amount of background introgression. Tx303 introgressions ranged in size from 10 to 150 cM, with an average of 60 cM. Across all NILs, 89% of the Tx303 genome is represented in targeted and background introgressions. The average proportion of background introgression was 2.5% (range 0 to 15%), significantly lower than the expected value of 6.25% for third backcross generation lines developed without marker-assisted selection. The NILs were grown in replicated field evaluations in two years to map QTLs for flowering time traits. A parallel experiment of testcrosses of each NIL to the unrelated inbred, Mo17, was conducted in the same environments to map QTLs in NIL testcross hybrids. QTLs affecting days to anthesis, days to silking, and anthesis-silk interval were detected in both inbreds and hybrids in both environments. The testing environments differed dramatically for drought stress, and different sets of QTLs were detected across environments. Furthermore, QTLs detected in inbreds were typically different from QTLs detected in hybrids, demonstrating the genetic complexity of flowering time. NILs can serve as a valuable genetic mapping resource for maize breeders and geneticists.