Detection of QTLs for vertical root pulling resistance in maize and overlap with QTLs for root traits in hydroponics and for grain yield under different water regimes

Vertical root pulling resistance (VRPR) is a trait used to estimate root strength in maize (Zea mays L.). Its measurement is laborious and destructive; hence, it would be beneficial to study root strength without resorting to VRPR and to conduct marker-assisted selection (MAS) for VRPR. The objectives of this investigation were: to identify, the chromosomal segments (quantitative trait loci, QTLs) controlling VRPR; to study the overlap of QTLs for VRPR and QTLs for both root traits in hydroponic culture and for grain yield under well-watered (GY-WW) and water-stressed (GY-WS) conditions; and to develop strategies of MAS at the detected QTLs. One-hundred eighteen F 3 families derived from Lo964 x Lo1016 were evaluated for VRPR (three locations, one year), for root traits in hydroponics (one trial), for GY-WS, GY-WW (one location, two years), and for a drought tolerance index (DTI) calculated as the ratio between GY-WS and GY-WW. For VRPR, 19 QTLs were detected in at least one location or for the mean across locations. Additive effects were positive for some QTLs and negative for others, consistent with the observed transgressive segregation. Ten of the QTLs for VRPR overlapped (i.e., their peaks were within a 10 cM interval) with at least one QTL for root traits in hydroponics. Eleven of the 19 QTLs for VRPR overlapped at least once with QTLs for GY-WW, GY-WS, and/or DTI. Three of the overlapping QTLs showed consistency of sign of additive effects for VRPR and for GY-WW, GY-WS and DTI. These three QTLs were on chromosome 1, one peaking near csu145, another between PGAMCTA205 and PGAMCGT400, and the third between PGAMCGG220 and csu2d; these QTLs also overlapped with QTLs for root traits in hydroponics. Results suggest that MAS can utilise these QTLs to improve both root characteristics and yield performance under WW and WS growing conditions.