In Vitro Pollination and Pollen Germination of Moringa oleifera Lam. Growing under Sub-optimal Growing Conditions in Gauteng, South Africa

Moringa oleifera Lam., a tree naturally grown in the tropics, is becoming increasingly popular as an industrial crop due to its multitude of useful attributes as water purifier, nutritional supplement, and biofuel. The tree originates from tropical areas (India) and tolerates sub-optimal growing conditions, but we are investigating the possibility of growing the crop in cooler climates with medium to low rainfall, such as the Gauteng Province. This study is therefore aimed at investigating the success of self- and cross-pollination of trees under the latter climatic conditions.    Ten trees were randomly selected in an 8-year-old Moringa oleifera orchard at the Experimental Farm of the University of Pretoria (25°45’S, 28°16’E) at an altitude of 1372 m above sea level and an average annual rainfall of 674 mm. For in vitro pollen germination, pollen was collected from five individual flowers at three stages a) early anthesis, b) one day after anthesis, and c) two days after anthesis. The hang drop method was applied, allowing pollen to germinate. Three slides for each stage were prepared. Germinated and ungerminated pollen were counted on each slide in five different microscopic fields. For semi-vivo pollen germination, flowers starting with anthesis were emasculated and bagged. On the second day the flowers were collected and self- and cross-pollinated and pedicels inserted in a congealed 1% agar + 0.02% boric acid + 10% sugar substrate in plastic dishes. For each self- and cross-pollination treatment, there were five replications with five flowers each. Flowers were incubated under a 12 h photoperiod and 60 µmol·m^-2·s^-1PAR using two cool-white fluorescent tubes per shelf. Temperatures were maintained at 24 ± 2 °C. After the second day flowers were fixed in Carnoy solution. The ovaries were softened, rinsed and stained. Squashed preparations were viewed under a confocal microscope. Fresh, one-day-old, and two-day-old pollen germinated equally well in vitro. There was no obvious difference in the number of ovules with penetrated pollen tubes between semi-vivo, self-, and cross-pollinated ovaries.  A high percentage ovules from both self- and cross-pollinated ovaries had branched pollen tubes at the entrance of the embryo sac.