Induced in vitro adaptation for salt tolerance in date palm (Phoenix dactylifera L.) cultivar Khalas

Soil salinity causes huge economic losses to agriculture productivity in arid and semiarid areas worldwide. The affected plants face disturbances in osmotic adjustment, nutrient transport, ionic toxicity and reduced photosynthesis. Conventional breeding approaches produce little success in combating various stresses in plants. However, non-conventional approaches, such as in vitro tissue culturing, produce genetic variability in the development of salt-tolerant plants, particularly in woody trees.

Embryogenic callus cultures of the date palm cultivar Khalas were subjected to various salt levels ranging from 0 to 300 mM in eight subcultures. The regenerants obtained from the salt-treated cultures were regenerated and evaluated using the same concentration of NaCl with which the calli were treated. All the salt-adapted (SA) regenerants showed improved growth characteristics, physiological performance, ion concentrations and K⁺/Na⁺ ratios than the salt non-adapted (SNA) regenerants and the control. Regression between the leaf Na⁺ concentration and net photosynthesis revealed an inverse nonlinear correlation in the SNA regenerants. Leaf K⁺ contents and stomatal conductance showed a strong linear relationship in SA regenerants compared with the inverse linear correlation, and a very poor coefficient of determination in SNA regenerants. The genetic fidelity of the selected SA regenerants was also tested using 36 random amplified polymorphic DNA (RAPD) primers, of which 26 produced scorable bands. The primers generated 1-10 bands, with an average of 5.4 bands per RAPD primer; there was no variation between SA regenerants and the negative control.

This is the first report of the variants generated from salt-stressed cultures and their potential adaptation to salinity in date palm cv. Khalas. The massive production of salt stress-adapted date palm plants may be much easier using the salt adaptation approach. Such plants can perform better during exposure to salt stress compared to the non-treated date palm plants.