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Physiological mechanisms controlling plant water use in maize
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Plants tend to decrease transpiration under water deficit and/or high evaporative demand by closing stomata and reducingleaf growth. Identification of sources of genetic variabilityfor underlying mechanisms is necessary to design genotypesadapted to stressing climatic scenarios. A series of four experimentswas performed in the PhenoArch image-based phenotypingplatform (M3P, France) with contrasting soil waterstatus and evaporative demand. We used a diversity panel of255 maize hybrids genotyped with 832K polymorphic SNPs.Equivalent stomatal conductance at plant level was estimatedin the studied 1680 x 4 plants by inversion of the PenmanMonteith equation. It changed with light intensity and vaporpressure deficit, with different thresholds and slopes betweengenotypes. Maximum values ranged from 52 to 76 mmol m-2sec-1 depending on hybrids. The sensitivity of leaf expansion tosoil water potential was calculated over the four experimentsas the slope of the relationship of leaf expansion rate to soilwater potential. For each hybrid, a common linear relationshipapplied to the four experiments. The x-intercepts of these relationships,which indicate the driest soil in which a plant stillhas an appreciable leaf growth, ranged from -0.6 to -1.6 MPadepending on hybrids. A GWAS analysis was performed on allvariables presented above, suggesting interesting candidategenes related to hydraulics and other mechanisms. Surprisingly,no co-location was observed between QTLs of stomatalconductance and of sensitivity to soil water deficit, supportingthe idea that the controls of stomatal opening/photosynthesisand of leaf expansion are largely independent.
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