Acclimation of Peanut to Water Stress Through Exposure to Differing Periods of Early Season Drought.

Peanut (Arachis hypogaea L.) is able to withstand drought either in early or late periods of the growing season, but suffers significant stress and yield loss during drought occurring in mid-season, coinciding with peak flower production and pod maturation.  In fact, periods of early drought stress often up-regulate physiological function through an acclimation response that allows the crop to better tolerate subsequent drought periods.  However, the optimum duration of early season drought stress is not known, such that an acclimation response is invoked but the crop is not detrimentally stressed.  Effects of the duration of early season water deficit were tested by applying 50% of ET for 0 (control), 10, 20, 30, 40, and 50 days after stand emergence, and then fully irrigating for the duration of the growth season subsequent to each stress period.  Genetic variability in acclimation response was examined in two peanut genotypes: one drought susceptible (Georgia Green: GG) and the other drought tolerant (C7616).  At each ten day stress period, physiological responses were measured both in a dry condition (three days without irrigation) and in a recovered condition (36 hours after irrigation).  Differential strategies of drought tolerance appeared to be operating in the two genotypes.  C7616 exhibited an acclimation response in both 10 and 40 day deficit treatments by maintaining physiological function in a dry condition above the control throughout most of the season. This acclimation ability was absent in GG, which was detrimentally affected by all deficit treatments.  C7616 exhibited a two stage tolerance strategy: a quick response to drought through modification of physiological function (10 day treatment); and further changes in function with increasing duration of drought (40 day treatment).  This ability to respond plastically to both short and long term drought may be part of the physiological foundation of peanut drought tolerance.