Recurrent Examination of Peanut Physiological Performance During the Progression of Water Stress Reveals Important Clues to the Mechanisms of Drought Tolerance.

Oftentimes crop drought tolerance is studied by the examination of two endpoints: one before stress is initiated and another at the maximal stress level.  The crop physiological performance is compared between these two extremes, commonly assuming a linear shape in the response curve.  However, the mechanisms involved in drought tolerance may be lost without looking more closely at the physiological changes occurring in between these two endpoints during the progression of drought stress.  To fully understand the mechanisms involved in peanut drought stress tolerance, a time step approach was taken involving daily measurements of gas exchange, chlorophyll fluorescence and NDVI during a 7-day dry down period in mid-season when the crop had reached peak physiological maturity.  Soil moisture drawdown was concurrently measured to document the soil water deficit conditions the crop was experiencing during the stress period.  Treatments were structured to test the acclimation potential of early season drought stress under different levels of deficit irrigation: season-long irrigation levels of 100%, 75%, and 50%; and early season deficit amounts of 50% and 75% up to 45 days after crop emergence followed by full rate (100%) irrigation for the remainder of the growing season.  Over the course of the 7-day measurement period, significant differences existed among treatments in nearly all of the measurements taken.  Most significantly, photosynthetic rates in the deficit irrigated plants were elevated in comparison to the 100% irrigated plants during the first five days of the stress period, even though photosynthetic levels were nearly identical across all treatments by the 7th day of stress.  Gas exchange rates were usually highest in the early season deficit treated plants indicating that early exposure to stress may be acclimating these plants to later season drought stress.