In order to evaluate the salt tolerance level of Jatropha curcas L., effects of salt stress on early growth and photosynthesis were investigated at Cairo University, Egypt, for salty irrigation use. Plants were cultivated in about 15 L plastic pots filled with field soil (Vertisol) and chemical fertilizer (5g, N:P2O5:K2O=8%:28%:24%). Salt treatments were started from 160 days after sowing as Experiment 1 in winter and 120 days after sowing as Experiment 2 in summer. 400mL of 0, 2000 and 4000 ppm NaCl solutions were irrigated every morning for 2 weeks. The highest soil EC was about 1mS cm-1, which was observed in 4000 ppm NaCl treatment. The photosynthetic rate of J. curcas was decreased under salt treatment conditions. Although photosynthetic rate was influenced by salt treatment, growth and dry weight were not. Fresh and dry weights of J. curcas were higher in Experiment 2 than those in Experiment 1, hence in winter in Cairo, J. curcas may not be able to grow sufficiently. Therefore, to confirm the maximum salty level for its cultivation, plants were cultivated under 0 ppm, 2000 ppm, 4000 ppm, 6000 ppm, and 8000 ppm NaCl treatments at University of Tsukuba, Japan, as Experiment 3. A high salt treatment solution affected to the dry weight of J. curcas at harvest severely, while under 7.5 mS cm-1 (≒4000ppm) solution showed about 82% of dry weight of the above ground part in control. In addition, lower leaves stored high content of Na, compared with upper and young leaves. It was estimated that J. curcas stored salt in lower leaves, not translocating it to upper and young ones to inhibit photosynthesis ability.
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