Fertilization and fruit setting in date palm: Biological and technological challenges

Control of pollination and fertilization in date palms is essential for development of high quality fruits. The female flower has three separate carpels. Only a single carpel develops into a fruit, while the others degenerate. When pollination is inefficient, non-fertilized flowers may develop into parthenocarpic fruits, which have no commercial value. The main aim of our research is characterization of fertilization and fruit setting in date palms and assessment of the effect of temperature on these processes. Since date is a very large tree, it is practically impossible to study its reproductive biology under completely controlled conditions, in a greenhouse or phytotron. Therefore, two alternative research approaches have been applied. In vitro assay was developed for culturing of isolated pollinated spikelets in liquid media under fully controlled conditions. Alternatively, the controlled environmental conditions were applied in planta, using specially designed units, assembled on pollinated inflorescences of whole date trees in the orchard. Each technique had specific advantages, as well as technical and biological limitations. Taken together, they complement as an efficient research tool. Relatively low temperatures (from 8 to 20°C) enhanced formation of parthenocarpic fruits and reduced normal fruit development. Temperatures also affected the rate of fruitlet development. Stages of pollen tube growth, fertilization, carpel development and/or degeneration, and early development of normal and parthenocarpic fruits were defined and characterized by macro- and microscopic analyses.