Promotive effects of a 5-aminolevulinic acid-based fertilizer on growth of tissue culture-derived date palm plants (Phoenix dactylifera L.) during acclimatization Mohamed A. Awad * Department of Arid Land Agriculture, College of Food and Agriculture, UAE University, P.O. Box 17555, Al-Ain, United Arab Emirates 1. Introduction Date palm is the most successful (and extremely important) subsistence crop in most of the hot arid desert regions (Botes and Zaid, 1999; Awad, 2007). There is a high demand for offshoots for new plantations but the number of offshoots which are naturally produced by fruiting palms is not sufficient (Awad, 2007). Recently, a special interest in date palm plants regenerated by tissue culture aroused since this technique can provide a large number of homogenous plants that are true to type and free of diseases and can be produced in large scale (Zaid and de Wet, 1999). However, the low survival rate together with the slow growth rate of the survived tissue culture-derived date palm plants during acclima- tization are critical problems facing the success of tissue culture as a commercial technique of date palm propagation. A survival rate of about 40–50% has been reported for some cultivars (Zaid and de Wet, 1999; Awad et al., 2006). The VP1-stage (in vitro plant in stage-1) is the most critical stage in the acclimatization program due to stresses caused by transplanting the plantlets ex vitro in pots under greenhouse. Also, date palm plants grow at a relatively slow rate and require a rather long acclimatization period of about 15– 24 months before transplanting to the open field conditions. Thus, treatments to enhance growth of plants and their tolerance to environmental stress are critically required to increase the survival rate and shorten the time of the acclimatization program. In higher plants, 5-aminolevulinic acid (ALA) is a key precursor of many tetrapyrrole compounds including porphyrins for chlorophyll biosynthesis (Stobart and Ameen-Bukhari, 1984). Several physiological effects of exogenous ALA have been found to regulate plant growth and increase productivity (Hotta et al., 1997a,b). ALA improves salt tolerance in cotton seedlings through the reduction in sodium uptake (Watanabe et al., 2000). Watanabe et al. (2004) reported a successful recovery from salt damage in cotton, tomato and wheat seedlings grown in Saudi Arabia by foliar spraying of ALA. Application of ALA as a plant growth regulator at Scientia Horticulturae 118 (2008) 48–52 ARTICLE INFO Article history: Received 31 May 2007 Received in revised form 24 May 2008 Accepted 26 May 2008 Keywords: Tissue culture Date palm Acclimatization 5-ALA Growth Chlorophyll ABSTRACT The low survival rate together with the slow growth rate of the survived tissue culture-derived date palm plants during acclimatization are critical problems facing the tissue culture as a commercial technique of date palm propagation. Growth parameters, pigment contents and nutrient uptake were examined in tissue culture-derived date palm plants (Phoenix dactylifera L.) c.v. ‘Khalas’ subject to different concentration of a 5-aminolevulinic acid-based fertilizer, commercially known as Pentakeep-v, during acclimatization. Pentakeep application at 0.02, 0.04 or 0.08% at 10 days interval significantly enhanced growth at both VP2- and VP3-stage of acclimatization. However, such effects were not detectable at the VP1-stage. At the end of this stage, the successful plants ranged from 66.6 to 78.3% with no significant differences between the Pentakeep treatments and the control. All successful plants at this stage survived both the VP2 and the VP3 stages of acclimatization. Plants treated with Pentakeep, especially at 0.04 and 0.08%, developed faster and were ready for transplanting to the nursery or to the open field conditions about 4–5 months earlier than the control or those treated with 0.02% Pentakeep. Pentakeep significantly increased chlorophyll a contents in all treatments which was subsequently reflected on total chlorophyll and chlorophyll a/chlorophyll b ratio. Pentakeep application, especially at the 0.08%, significantly increased the concentration of N, Cu and Zn in the leaves of treated plants. The concentration of available P and Zn in the soil was significantly higher in the Pentakeep treatments than the control. ß 2008 Elsevier B.V. All rights reserved. * Permanent address: Faculty of Agriculture, Pomology Department, Mansoura University, El-Mansoura, Egypt. Tel.: +971 3 7133361; fax: +971 3 7632384. E-mail address: mohamedawad@uaeu.ac.ae. Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti 0304-4238/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2008.05.034