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Cultivars of groundnut ( Arachis hypogaea L.) were subjected to a period of reduced soil water supply during early reproductive development. During the period of water deficit, total biomass production of two Virginia type cultivars (Virginia Bunch and Q18801) was greater than that of a Spanish type cultivar (McCubbin), even though all cultivars used similar amounts of radiation and water. Hence, the radiation use efficiency and transpiration efficiency of Q18801 were significantly greater than those of McCubbin. The radiation use efficiency of the stressed crops was only about 45% of those that were fully irrigated. Throughout the period of water deficit, noon leaf water potential was lowest in McCubbin in both treatments. In the well-watered treatment, this was associated with a higher leaf temperature and lower leaf conductance, than in the Virginia cultivars. Under increasing soil water deficit, the leaves of McCubbin tended to wilt, while the Virginia cultivars displayed active leaf folding. Thus, the ratio of the fraction of radiation intercepted by the canopy to leaf area index (LAI) was always lower in the Virginia type cultivars. For a given LAI, this phenomenon may have allowed these cultivars to decrease the effective atmospheric demand within the canopy, while maintaining radiation interception at saturation for photosynthesis. The consequence of this, given that the supply of water from the roots did not differ, was that Q18801 was able to maintain a higher LAI and a greater crop transpiration efficiency (ratio of biomass production to transpiration) than McCubbin. The existence of differences among cultivars in transpiration efficiency under drought may prove useful in improving adaptation of groundnut to these environments. |
