Mapping QTL for traits associated with resistance to ferrous iron toxicity in rice (Oryza sativa L.), using japonica chromosome segment substitution lines.

A mapping population of 66 japonica chromosome segment substitution lines (CSSLs) in indica genetic background, derived from a cross between a japonica variety Asominori and an indica variety IR24 by the single-seed descent, backcrossing and marker-assisted selection, was used to detect quantitative trait loci (QTLs) for leaf bronzing index (LBI), stem dry weight (SDW), plant height (PH), root length (RL) and root dry weight (RDW) under Fe2+ stress condition in rice. Two parents and 66 japonica CSSLs were phenotyped for the traits by growing them in Fe2+ toxicity nutrient solution. A total of fourteen QTLs were detected on chromosome 3, 6, 7, 9, 11 and 12, respectively, with LOD of QTLs ranging from 2.72 to 6.63. Three QTLs controlling LBI were located at the region of C515-XNpb279, R2638-C1263 and G1465-C950 on chromosome 3, 9 and 11, their contributions to whole variation were 16.45%, 11.16% and 28.02%, respectively. Comparing with the other mapping results, the QTL for LBI located at the region of C515-XNpb279 on chromosome 3 was identical with the QTL for chlorophyll content on a rice function map. The results indicated that ferrous iron toxicity of rice is characterized by bronzing spots on the lower leaves, which spread over the whole leaves, causing the lower leaves to turn dark gray and to product chlorophyll catabolites or derivatives which reduce cytotoxicity of some heavy metals, such as ferrous iron. Furthermore, the QTL for LBI, SDW and RDW located at the region of G1465-C950 on chromosome 11 is a major QTL. Whether the QTL for SDW, PH, RL and RDW at the region of XNpb386-XNpb342 on chromosome 6 is associated with resistance to ferrous iron toxicity need further studies. Our goal is to identify breeding materials for resistance to Fe2+ toxicity through marker-assisted selection based on the detected markers.