A conservative pattern of water use, rather than deep or profuse rooting, is critical for the terminal drought tolerance of chickpea

Abstract

Chickpea is mostly grown on stored soil moisture, and deep/profuse rooting has been hypothesized for almost three decades to be critical for improving chickpea tolerance to terminal drought. However, temporal patterns of water use that leave water available for reproduction and grain filling could be equally critical. Therefore, variation in water use pattern and root depth/density were measured, and their relationships to yield tested under fully irrigated and terminal drought stress, using lysimeters that provided soil volumes equivalent to field conditions. Twenty chickpea genotypes having similar plant phenology but contrasting for a field-derived terminal drought-tolerance index based on yield were used. The pattern of water extraction clearly discriminated tolerant and sensitive genotypes. Tolerant genotypes had a lower water uptake and a lower index of stomatal conductance at the vegetative stage than sensitive ones, while tolerant genotypes extracted more water than sensitive genotypes after flowering. The magnitude of the variation in root growth components (depth, length density, RLD, dry weight, RDW) did not distinguish tolerant from sensitive genotypes. The seed yield was not significantly correlated with the root length density (RLD) in any soil layers, whereas seed yield was both negatively related to water uptake between 23–38 DAS, and positively related to water uptake between 48–61 DAS. Under these conditions of terminal drought, the most critical component of tolerance in chickpea was the conservative use of water early in the cropping cycle, explained partly by a lower canopy conductance, which resulted in more water available in the soil profile during reproduction leading to higher reproductive success.