EFFECTS OF PEG-INDUCED WATER-STRESS ON 2 CITRUS CULTIVARS

The effect of polyethylene glycol (PEG) 4000 on sour orange (SO) and Cleopatra mandarin (CM) rootstock seedlings grown in fine sand under greenhouse conditions was studied. The PEG treatments were initiated by adding PEG to half strength Hoagland's solution to achieve final osmotic potentials of -0.10, -0.20, and -0.35 MPa. The no PEG control treatment had an osmotic potential of -0.05 MPa. Seedlings were harvested 6 months after starting PEG treatments. No significant differences in growth, root hydaulic conductivity, water flow rate, stomatal conductance, and evapotranspiration were detected between SO and CM. However, all these variables were significantly reduced by PEG. At a relatively low PEG level (-0.10 MPa), shoot and root dry weights, stem cross sectional area, total leaf area, and fibrous root length were reduced by more than 60%. Although SO and CM were similarly sensitive to PEG-induced water stress, significant differences between these two rootstocks were found in leaf mineral composition, chlorophyll content, leaf succulence, and specific leaf weight. PEG reduced N, K, and Mg, increased P, Ca, Zn, Mn, and Fe leaf contents, but did not affect Cu leaf content. PEG-treated seedlings produced heavier leaves per unit area and heavier roots per unit length than nontreated seedlings.