A common genetic determinism for sensitivities to soil water deficit and evaporative demand : meta-analysis of QTLs and introgression lines of maize

Evaporative demand and soil water deficit equally contribute to water stress and to its effect on plant growth. We have compared the genetic architectures of the sensitivities of maize leaf elongation rate to evaporative demand and to soil water deficit. The former was measured via the response to leaf-to-air vapour pressure deficit in well-watered plants, the latter via the response to soil water potential in the absence of evaporative demand. Genetic analyses of each sensitivity were performed over 21 independent experiments with (i) three mapping populations, with temperate or tropical materials, (ii) one population resulting from the introgression of a tropical drought tolerant line in a temperate line (iii) two introgression libraries genetically independent from mapping populations. A very large genetic variability was observed for both sensitivities. Some lines maintained leaf elongation at very high evaporative demand or water deficit while others stopped elongation in mild conditions. A complex architecture arose from analyses of mapping populations, with 19 major metaQTLs involving strong effects and/or more than one mapping population. 68% of those QTLs affected sensitivities to both evaporative demand and soil water deficit. In introgressed lines, 73% of the tested genomic regions affected both sensitivities. This study is the first genetic demonstration that hydraulic processes, which drive the response to evaporative demand, also have a large contribution to the genetic variability of plant growth under water deficit in a large range of genetic material.