Research paperThe 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

•Pollen source and pollination time can improve fruit set of TC-derived 'Barhee' trees.•'Zahidi' pollen was the best pollen source to maximize normal fruit set and bunch yield.•'Jarvis No.1' pollen was concluded as the best source to improve fruit physical traits.•Pollination at day of natural spathe cracking (DNC) was the best pollination date.

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.