Investigation of physiological and biochemical responses of Cadaman andGF677 stone fruit rootstocks under drought stress

In this study, the drought tolerance threshold and relationships between some biochemical and physiological responses of two stone fruit rootstocks, Cadaman and GF677, have been investigated. For this purpose, a pot experiment has been carried out in a greenhouse using factorial trial based on a completely randomized design with three replications. One-year-old rooted cuttings of two rootstocks are exposed to drought stress (-0.1 (control), -0.6, -1.1, -1.6 MPa) by adding different amounts of polyethylene glycol-6000 to Hoagland nutrient solution. Significant increase in electrolyte leakage and decrease in leaf relative water content of Cadaman and GF677 rootstocks has occurred at -0.6 and -1.1 MPa, respectively. Concentration of photosynthetic pigments and quantum yield of photosystem II (FV/FM) are less affected by drought stress, decreasing significantly in Cadaman and GF677 rootstocks at -1.1 and -1.6 MPa, respectively. Under severe drought stress, photosynthesis, transpiration, intercellular CO2 concentration, and stomatal conductance in Cadaman rootstock decline more considerably, compared to GF677. Moreover, at drought stress of -1.6 MPa, GF677 does not significantly reduce its photosynthesis, despite a substantial decrease in transpiration; however, the relative decrease in photosynthesis of Cadaman at -1.6 MPa has been much greater than the relative decrease in its transpiration and intercellular CO2 concentration, which, in turn, results in a drop in water use efficiency and mesophilic conductance of Cadaman leaves, compared to GF677. It seems that considerable reduction in photosynthesis in Cadaman rootstock, along with stomatal limitations, is largely due to non-stomatal constraints such as loss of cell membrane intact and reduction of chlorophyll, carotenoids and chlorophyll fluorescence. Results show that GF677 rootstock has higher tolerance to severe drought stress, compared to cadaman.