Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Research paper The strong effect of pollen source and pollination time on fruit set and the yield of tissue culture-derived date palm (Phoenix dactylifera L.) trees cv. Barhee Nasim Mohammadi a , Sasan Rastgoo a, ⁎ , Mahmood Izadi b a Department of Horticultural Science, Faculty of Agriculture and Natural Resources, Persian Gulf University, Borazjan, Bushehr, Iran b Scientific Faculty of Agricultural and Natural Resources Research and Education Center, Fars, Iran ARTICLE INFO Keywords: Date palm Barhee Phoenix dactylifera L. Fruit set Pollen source Pollination time ABSTRACT Generally, abnormal fruit set mostly in the form of setting parthenocarpic triple fruitlets is one of the most economically important disorders, which appears in trees of numerous TC (tissue culture)-derived date cultivars including cv. ‘Barhee'. To improve normal fruit set, fruit yield and fruit quality of such Barhee trees, effect of five pollen sources (three endogenous sources; ‘Beraim’, ‘Shahani’ and ‘Zahidi’ and two internationally recognized varieties; ‘Fard No. 4’ and ‘Jarvis No. 1’) at two pollination times (day of natural spathe cracking (DNC) 1 and two days later (DNC+2) 2 ) was investigated on young TC-derived ‘Barhee’ trees. The study was conducted as split- plot in a randomized complete block design (RCBD), replicated three times, in hot, arid region of the southwest of Iran during the year 2013. The results indicated that the ‘Zahidi’ pollen had caused the highest percentage of normal fruit set (avg. 50.1%) and bunch yield (3.55 kg) significantly (P ≤ 0.05) superior than the other pollen sources, followed by Jarvis No. 1 (36.6%). The pollination with ‘Beraim’ pollen produced the lowest percentage of normal fruits (21.3%). The pollination at DNC was significantly (P ≤ 0.05) higher in normal fruit set and bunch yield. The pollination with ‘Zahidi’ pollen at DNC brought the highest percentage of normal fruit set (57.5%) and maximum bunch yield (4.59 kg) with acceptable fruit weight and size. Both mentioned factors and the interactive effect significantly (P ≤ 0.05) influenced bunch ripeness. The pollen of ‘Jarvis No. 1’ at DNC yielded the highest percentage of bunch ripeness (96.91%). This pollen which had the second best normal fruit set and bunch yield was superior in showing off key metaxeic effects i.e. fruit volume, fruit weight, and pulp to seed ratio (w/w). The pollination at DNC significantly (P ≤ 0.05) led to higher fruit length, diameter, volume and weight. Ultimately, we concluded ‘Zahidi’ pollen as the best choice for increasing normal fruit set and economical yield, ‘Jarvis No. 1’ pollen as the most suitable pollen source to benefit metaxenic effects and DNC as the best time for pollination of the TC-derived Barhee trees exhibiting abnormal fruit set and poor yield. 1. Introduction Date palm (Phoenix dactylifera L.) is one of the most important, widely grown commercial tree crops in Iran. With production of over one million tons, Iran is the world’s second largest date producer (FAOSTAT, 2013). Among numerous date palm cultivars, ‘Barhee’ is one of few superior, elite and renowned ones in the world and in Iran as well. Barhee dates are best marketed at khalal stage (physiologically mature, hard ripe and the color changes completely from green to opaque yellow); however the khalals of most date cultivars are not edible due to high tannin and low sugar. On the other side, yield of Barhee cultivar is comparatively high, reaches an average of 200 kg per palm (Zaid and de Wet, 2002a) and ensures higher income for the grower, which in turn motivates great demand for its propagule to expand its plantations while it is in short supply. Barhee's offshoot production is low (usually only 3–5 per palm) (Zaid and de Wet, 2002a) and even sometimes only about 30 percent of the trees are able to produce this low number (Smith and Aynsley, 1995). This challenge has led the people to focus on micropropagation technique during the past 30 years as a means for rapid clonal re- production of highly desirable cultivars. However, despite numerous advantages of in vitro propagation of date palm, this technology has also caused some problems in growth and yield of TC (tissue culture)-derived trees. Genetic fidelity, http://dx.doi.org/10.1016/j.scienta.2017.06.031 Received 19 March 2017; Received in revised form 12 May 2017; Accepted 14 June 2017 ⁎ Corresponding author at: Department of Horticultural Science, Faculty of Agriculture and Natural Resources, Persian Gulf University, Borazjan 7561158808, Bushehr, Iran. E-mail addresses: rastgoo@pgu.ac.ir, snrastgoo@yahoo.com (S. Rastgoo). 1 DNC; day of natural spathe cracking. 2 DNC+2; two days after DNC. Scientia Horticulturae 224 (2017) 343–350 0304-4238/ © 2017 Published by Elsevier B.V. MARK