Marker-assisted introgression of qHSR1 to improve maize resistance to head smut

Head smut, one of the most devastating diseases in maize, causes severe yield losses worldwide. Resistance to head smut has been proven to be a quantitative inherited trait. In our previous study, a major resistance quantitative trait locus (named qHSR1) was detected on maize chromosome 2 (bin 2.09), and a number of molecular markers have been developed in the qHSR1 region. Here, we report the marker-assisted introgression of qHSR1 to improve maize resistance to head smut. The 10 maize inbred lines, namely Ji853, 444, 98107, 99094, Chang7-2, V022, V4, 982, 8903, and 8902, which have high yield potential but are susceptible to head smut, were selected for resistance improvement. Each of the 10 high-yielding lines was crossed with a donor parent Ji1037 that is completely resistant to head smut, followed by five generations of backcrossing to the respective recurrent parent. Marker-assisted foreground selection was conducted to identify qHSR1. Recombinant selection was carried out in the fourth backcross (BC4) generation by using the flanking markers to reduce the size of the Ji1037 donor segment carrying qHSR1. Background selection was performed in the BC5 generation with genome-wide SSR markers to select the line with the highest recovery rate of the recurrent parent genome. Self-pollination was conducted twice for the BC5 plant with both the shortest qHSR1 region and the highest recovery rate to obtain converted inbred lines harboring qHSR1. The 10 converted inbred lines all showed substantial improvement in resistance to head smut. Furthermore, the hybrids prepared from the converted lines also showed significant increase in resistance to head smut, while remaining mostly unchanged for other agronomic traits.