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Identification and Fine-Mapping of a Novel QTL qMrdd2 Conferring Resistance to Maize Rough Dwarf Disease.

Maize rough dwarf disease (MRDD), caused by a virus, seriously affects maize quality and yield worldwide. MRDD can be most effectively controlled with disease-resistant hybrids of corn. Here, MRDD-resistant (Qi319) and -susceptible (Ye478) parental inbred maize lines and their 314 recombinant inbred lines (RILs) that were derived from a cross between them were evaluated across three environments. A stable resistance QTL, qMrdd2, was identified and mapped using BLUP values to a 0.55 Mb region between the markers MK807 and MK811 on chromosome 2 (B73 RefGen_v3), which was found to explain 8.6 to 11.0% of the total phenotypic variance in MRDD resistance. We validated the effect of qMrdd2 using a chromosome segment substitution line (CSSL) that was derived from a cross between maize inbred Qi319 as the MRDD resistance donor and Ye478 as the recipient. Disease severity index of the CSSL haplotype II harboring qMrdd2 was significantly lower than that of the susceptible parent Ye478. Subsequently, we fine-mapped qMrdd2 to a 315 kb region flanked by the markers RD81 and RD87 by testing recombinant-derived progeny using selfed backcrossed families. In this study, we identified a novel QTL for MRDD-resistance by combining the RIL and CSSL populations, which can be used to breed for MRDD resistant varieties of maize. Keywords: Maize, Maize rough dwarf disease, QTL, Fine-mapping, Recombinant inbred line, Chromosome segment substitution line.