Introgression of QTLs determining sorghum downy mildew (SDM) resistance into elite maize line UMI 79 through marker-assisted backcross breeding (MABC)

Abstract

Sorghum downy mildew (SDM), caused by Peronosclerospora sorghi is one of the important diseases in maize. Here, we illustrate the transfer of two QTLs for SDM on chromosome 3 and 6 from UMI 936 (w) into an elite maize inbred line UMI 79 through marker-assisted backcross breeding (MABC). For foreground selection, plants carrying heterozygote allele for the QTLs for SDM were selected from F1 and three back cross (BC1-BC3) generations using simple sequence repeat (SSR) markers linked to the targeted QTLs region of SDM. Consequently, foreground positive plants from BC3F1 generation selfed to produce BC3F2 and plants carrying the favorable alleles for the QTLs for SDM were selected followed by stringent phenotyping against SDM and advanced to BC3F3. As a result, two improved lines (79/936–1–7-7-7-46-46 and 79/936–1–7-7-10-80-80) possessing QTLs for SDM were obtained. Background selection using 146 SSR markers distributed evenly across the maize genome revealed 92.45% and 89.68% recovery of recurrent parent genome (RPG) in two improved lines. Phenotypic characterization of the improved lines showed more than 90% of recovery of the recurrent parents in morphological traits and a resistance to SDM. In conclusion, the newly developed SDM resistant inbred lines are a potential source for improving SDM resistance in maize breeding programs.