QTL mapping for root architecture and transpiration efficiency in a maize introgression library

High transpiration efficiency (TE) is one way to optimize water use. Although variation for root morpho-physiological traits can strongly affect the water status of a plant, the relationship between root traits and TE is not well understood. A maize introgression library (IL) derived from the cross between Gaspe Flint (an early line; donor parent) and B73 (an elite line; recurrent parent) were evaluated in order to identify QTLs for root system architecture (RSA), total biomass (TB), leaf area (LA), transpiration rate (TR), transpiration efficiency (TE), flowering time (FT), grain yield (GY) and yield components (YC). Two different experiments were carried out in order to study the genetic control of i) RSA, FT, GY and YC in response to drought in field conditions, at UNIBO, Italy and ii) TE, TR, TB and LA in controlled environment at different VPD, at ICRISAT, India. Differences in leaf area among the IL lines explained only 40% of the transpiration differences under high evaporative demand. QTLs were identified for all investigated traits. Overlaps between root and transpiration-related QTLs were detected on chromosomes 1 and 8. At these QTLs, the Gaspe Flint allele was associated with a TE decrease. A particularly interesting QTL for GY and YC, FT and TR was mapped on chromosome 3 (bin 3.3) where the Gaspe Flint allele was associated with an increase of both yield and transpiration rate and earliness.