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Background: Maize rough dwarf disease (MRDD) is a disease caused by a virus that seriously affects maize yield and quality worldwide. Rice black streaked dwarf virus (RBSDV) in the Fijivirus genus in the Reoviridae family causes MRDD in maize. Typical MRDD symptoms of include severe dwarfing of plants, shortening of internodes. MRDD resistance is a complex trait that is quantitatively inherited and is controlled by several quantitative trait loci (QTL). MRDD is most efficiently controlled by the cultivation of disease-resistant corn hybrids. Results: Disease resistance in the MRDD-resistant Qi319 and -susceptible Ye478 parental inbred lines and the 314 recombinant inbred lines (RILs) that were derived from a cross between them was evaluated across three environments. A stable resistance QTL, qMrdd2 , which explained 8.64 to 11.02% of the total phenotypic variance in MRDD resistance, was identified repeatedly and was mapped using BLUP values to a 0.55-Mb region between the markers MK807 and MK811 on chromosome 2. We validated the effect of qMrdd2 using a chromosome segment substitution line population that were derived from a cross between maize inbred Qi319 as the resistance donor and Ye478 as the recipient. The disease-severity index (DSI) of CSSL haplotype II harboring qMrdd2 was significantly lower than the DSI of susceptible parent Ye478 ( P < 0.05). Mapping results using CSSLs were consistent with localization interval determined using RILs. The qMrdd2 locus acted with an additive effect but no significant dominant gene action in conferring MRDD resistance. We fine-mapped qMrdd2 locus into a 315-kb region flanked by the markers RD81 and RD87 by testing recombinant-derived progeny using selfed backcrossed families. Conclusions: qMrdd2 is a recently discovered QTL from Qi319 for resistance to MRDD with an additive effect but no significant dominant gene action for MRDD resistance. qMrdd2 was fine-mapped to a 315-kb interval on maize chromosome 2. Introgression of the MRDD resistance allele at the qMrdd2 locus of CSSL haplotype 2 using linked markers umc1824 and bnlg125 will be useful for maize breeding to reduce yield losses caused by MRDD. Keywords: Maize, Maize rough dwarf disease, QTL, Fine-mapping, RIL；CSSL.