Abstract
Date palms growing in hot arid regions are generally facing several kinds of environmental stresses, especially salinity and aridity, which limit growth of young trees in newly established orchards and thus might negatively affect future tree productivity and fruit quality. Growth parameters, pigment contents and nutrient uptake were examined in young tissue culture-derived date palm trees (Phoenix dactylifera L.) cv. 'Barhee' subjected to foliar application of 5-aminolevulinic acid (5-ALA) at different rates in a newly established orchard. The results showed that after 20 months from transplanting all the trees were successfully developed and well established without any losses. After 12 months from transplanting, the tree height was not significantly affected by 5-ALA application compared to control. However, after 20 months from transplanting, the tree height was significantly higher at 50 and 100 ppm of 5-ALA application compared to control, while 5-ALA application at 150 ppm had no significant effect on tree height compared to control. The crown circumference was significantly increased by 5-ALA application at 100 ppm compared to control after both 12 and 20 months following transplanting. Leaf number was not significantly affected by 5-ALA application and was highest at 100 ppm. Chlorophyll a concentration was significantly higher at 50 and 100 ppm of 5-ALA application than in control. However, chlorophyll b was not affected by 5-ALA application. Total chlorophyll concentration was significantly higher at 50 and 150 ppm of 5-ALA application than in control. Chlorophyll a/b ratio was not significantly affected by 5-ALA application. The higher rate of 5-ALA application (150 ppm) has no significant effect on tree growth parameters or chlorophyll a concentration compared to control. The concentration of N, K and Na, and the K/Na ratio in tree leaves was not affected by 5-ALA application, while P concentration was significantly higher at 50 and 150 ppm of 5-ALA application than in control. It was concluded that 5-ALA application enhanced growth of young tissue culture-derived 'Barhee' date palm trees in a newly established orchard by increasing chlorophyll concentration and possibly photosynthetic assimilation.