Abstract

Salt and heat stresses are one of the greatest constraints facing agricultural production worldwide, particularly in arid and semi-arid countries where scarcity of water and high temperatures prevail. Assessing tolerance level of date palm trees regenerated by tissue culture against heat and salt stresses is a prerequisite.This investigation aims to determine heat and NaCl tolerance of date palm (cv. Ruzaiz) produced by tissue culture and offshootas well as to study the possibility of increasing tolerance to heat stress alone or in the presence of NaCl stress by using calcium, potassium or oleic acid by using electrolyte leakage methodwhich based on sigmoidal curves at 50 %. Tissue culture plants used in this investigation were at 4 and 10 months old vitro plants namely; VP2 and VP3, respectively as well offshoots from the same variety attached to mother plant in the field.Electrolyte leakage method was used to determine thermo-tolerance of leaf tissues.  Leaf segments of five-centimeter length from VP2, VP3 and off shoots were assayed in the laboratory for tolerance totreatments (heat, heat plus NaCl, heat plus KCl, heat plus CaCl₂, heat plus oleic acid, heat plus NaCl and oleic acid, heat plus NaCl and KCland heat plus NaCland CaCl₂.  The concentrations of the test compounds were: NaCl at 1% w/v, KCl or CaCl₂ (0.2 M) or oleic acid (0.1 M).  A completely randomized design was used with three replications. The results revealed that thermo-tolerance values were 53, 53.5, and 58.5°C for VP2, VP3, and offshoot leaflets, respectively. Also there is a potential to increase the thermo-tolearance of VP2, VP3, or offshoots that could increase their survival under field conditions by pretreatment with KCl, CaCl₂ (0.2 M) or oleic acid (100 ppm).

Key words: Electrolyte leakage, thermo-tolerance, membrane stability, salinity, lethal temperature, heat regime, semipermeability.