QTL analysis of low nitrogen tolerance in rice seedlings based on chromosome segment substitution lines

Objective  To map the quantitative trait loci (QTL) associated with low nitrogen tolerance in rice (Oryza sativa), provide a basis for future fine mapping, cloning and functional characterization of related genes and offer theoretical references for breeding of low nitrogen tolerant rice.

Method  A set of chromosomal segment substitution lines which was constructed by crossing Koshihikari (recurrent parent) and Nona Bokra (donor parent) were used as test materials. Low nitrogen stress treatment was applied at rice seedling stage. The relative loss ratios of eight phenotypes including rice plant height, root length, root fresh weight, root dry weight, shoot fresh weight, shoot dry weight, total fresh weight and total dry weight were analyzed, and QTL mapping was performed.

Result  Two loci related to low nitrogen tolerance of rice were successfully mapped. These two QTLs were qRL1-1 and qRFW2-1 which were related to root length and root fresh weight respectively under low nitrogen stress. qRL1-1 was closed to the M1-29 marker on chromosome 1 with a LOD score of 2.89 and explained about 11.23% of total phenotypic variance. qRFW2-1 was closed to the M2-225 marker on chromosome 2 with a LOD score of 2.53 and explained about 9.90% of total phenotypic variance. No loci was found for other six phenotypic indexes.

Conclusion  QTLs related to root length and root fresh weight under low nitrogen stress are mapped, which lays the foundation for further genetic fine mapping and cloning of the underlying genes.