Marker-assisted selection of qMrdd8 to improve maize resistance to rough dwarf disease

Maize rough dwarf disease (MRDD) is caused by viruses in the Fijivirus genus in the family Reoviridae. MRDD resistance can be improved by a combination of marker-assisted selection (MAS) and conventional breeding strategies. In our previous study, we fine-mapped a major QTL qMrdd8 and developed the functional Indel marker IDP25K. In the present study, qMrdd8 from the donor parent X178 was introgressed into elite inbred lines derived from the three corn heterotic groups using multi-generation backcrossing and MAS. Recipient lines included Huangzao4, Chang7-2, Ye478, Zheng58, Zhonghuang68, B73, and Ji846. Markers used for foreground selection included IDRQ4, IDRQ47, IDP25K, and IDP27K. Background selection was carried out in the BC(3) or BC(4) using 107 SSR markers to select lines with the highest rate of recovery of the particular recurrent parent genome. Plants from BC(4)F(2) and BC(3)F(2) that carried the shortest qMrdd8 interval from X178 and those with the highest rate of recovery of the recurrent parent genome were then selected to create converted homozygous inbred lines. In 2017, seven converted inbred lines and five hybrids exhibited enhanced resistance to MRDD, while other agronomic traits were not affected under nonpathogenic stress conditions. Thus, the MRDD resistance allele at the qMrdd8 locus, or IDP25K, should be valuable for maize breeding programs in China.