Marker-assisted selection of <i>qMrdd8</i> to improve maize resistance to rough dwarf disease

Abstract

Maize rough dwarf disease (MRDD) is caused by viruses in the <i>Fijivirus</i> genus in the family <i>Reoviridae</i>. 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 <i>qMrdd8</i> and developed the functional Indel marker IDP25K. In the present study, <i>qMrdd8</i> 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 BC₃ or BC₄ using 107 SSR markers to select lines with the highest rate of recovery of the particular recurrent parent genome. Plants from BC₄F₂ and BC₃F₂ that carried the shortest <i>qMrdd8</i> 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 <i>qMrdd8</i> locus, or IDP25K, should be valuable for maize breeding programs in China.