Response of Maize ( Zea mays L.) Hybrids to Diurnal Variation of Vapor Pressure Deficit (VPD) and Progressive Soil Moisture Depletion

This study investigated the transpiration (TR) response to (i) diurnal changes of vapor pressure deficit (VPD) and (ii) soil dry down in four maize hybrids contrasting for yield performance under drought stress in the field. These four hybrids included a popular local variety P3K and a commercial check SC303 that were found to be drought susceptible. The experiment was carried out in pots at early vegetative stage (8-leaf stage). Results showed an increase of TR with increasing VPD but with significant variations between the hybrids tested. The two susceptible hybrids P3K and SC303 had higher TR over nearly the whole range of VPD values than the two other hybrids, with the largest variation recorded at VPD values above 6 kPa. Regarding the TR response to soil moisture depletion, normalized TR (NTR) of all genotypes reduced with soil moisture depletion for all treatments. In addition, NTR showed a significant reduction for plants that were irrigated at 3 days intervals before the experiment as compared to those irrigated daily. There was a trend of higher water extraction, as evaluated with the fraction of transpirable soil water (FTSW) threshold, in the tolerant hybrids relative to the susceptible ones for the two irrigation treatments. In addition, prior exposure to water deficit tends to lower the FTSW threshold which leads to increased water extraction capacity at lower soil moisture level. These results demonstrate that control of TR under high VPD conditions coupled with high water extraction capacity from progressively drying soil can contribute to drought tolerance in maize hybrids.