An appraisal of pollen germination and viability of varied male pollen sources of date palm (Phoenix dactylifera L.)

Abstract: Date palm is a dioecious fruit tree that permits cross pollination for fruit setting. The germination of viable pollens to fertilize ovule is influenced by environmental cues such as temperature. The germination and viability of pollen grains collected for pollination purpose also varied with the male pollinizer source and the male spathe opening time. An in vitro study performed to determine the percentage of pollen germination at different temperatures (10, 15, 20, 25, and 30 °C) and germination times (4, 8, 12, and 24 h) taken from different male sources and toidentify any variations in the germination and viability of pollen grains collected from spathes opened at different dates (20^th February, 1^st and 10^th March). Pollens from different male sources showed a significant difference regarding germination percentage when incubated at different temperatures and for different germination times. Pollens incubated at 30 (81.07%) and 25°C (78.17%) had the highest germination percentage which decreased to 51.04, 16.23, and 5.90% when incubation temperature dropped to 20, 15, and 10 °C, respectively. Similarly, 71.11% pollens were germinated after 4 h of incubation at 30°C, which was decreased to 63.26 and 25.40% when incubation temperature decreased to 25 and 20°C, respectively after same time interval. Pollen germination and viability were significantly differed when they were collected from spathes opened at three different dates. Early opened spathes had lowest germination (57.58%) and viability percentages (81.19%) than the middle (81.11 and 91.53%) or late (80.71% and 93.05%) opening spathes. It is therefore, concluded that the optimum temperature for date palm pollen grains germination is 25-30°C and at these temperatures maximum pollens germinated within 4 h. Moreover, pollen grains from early opened spathes were less superior compared to the middle or late opening ones.