Drought tolerance mechanisms for yield responses to pre-flowering drought stress of peanut genotypes with different drought tolerant levels

A better understanding of the mechanisms of peanut adaptation to pre-flowering drought is important for improving pod yield productivity. Nevertheless, the mechanisms of drought tolerance are under different genetic controls, and pod yield is a complex trait. Therefore, the aim of this study was to investigate the mechanism for drought tolerance of peanut genotypes with different pod yield responses under pre-flowering drought conditions. Field experiments were conducted during February to July, 2007 and during February to July, 2009. A split-plot experiment in a randomized complete block design was used. Two water management treatments were assigned as the main plots, i.e. field capacity (F.C.) and pre-flowering stress (PFD), and six peanut genotypes as the sub-plots. Relative water content (RWC) and stomatal conductance were recorded at 5, 10, 15, 20, 25, 30, 35 and 40 days after emergence (DAE). Leaf area index was measured at 25 DAE, R5 and R7. Total dry matter samples, including shoots, roots and pods, were obtained at 25 DAE, R5, R7 and harvest. Shoot growth rate, root growth rate and pod growth rate were then calculated. Major finding, the first mechanism is explained by high water uptake of the root systems that provide sufficient water for normal transpiration, as the response of ICGV 98305 to PFD. It may induce the improvement of peanut pod growth rate in pod filling stage due to the change of assimilate proportion, resulting in increasing pod yield to PDF comparing with adequate water conditions. In contrast, such as the response of ICGV 98330, pre-flowering drought can increase the ability of peanut to save more water by reduction of transpiration, but rooting traits are not changed. This could conserve more water by reducing transpiration to maintain high RWC. Nevertheless, the ability to reduce transpiration did not support the improvement of peanut pod yield under these conditions. The increasing peanut productivity to pre-flowering drought was contributed by the improvement of assimilate proportion to economic part in reproductive phase. This knowledge will be useful for breeding of peanut for pre-flowering drought environment.

► High water uptake of root system provides sufficient water for normal transpiration.
► The change in assimilate proportion is a key to improve peanut yield under PFD conditions.
► Pod yield might be increased by the improvement of pod growth rate in pod filling stage.
► Decreased transpiration occurs did not encourage the improvement of peanut pod yield.