A. Torahi - Department of Horticultural Science, Tarbiat Modares University (TMU), Tehran, Islamic Republic of Iran. Present address: Date Palm and Tropical Fruits Research Centre, Horticultural Science Research Institute, Agricultural Research , Education and Extens
K. Arzani - Department of Horticultural Science, Tarbiat Modares University (TMU), Tehran, Islamic Republic of Iran.
N. Moallemi - Department of Horticultural Science, Shahid Chamran University, Ahvaz, Islamic Republic of Iran.

This experiment was conducted to determine the effects of dust, rain, and pollination on photosynthesis activity and crop yield of commercial date palm (Phoenix dactylifera L.) cultivar `Sayer’. Mature trees were used for dust treatments application and assessments under Ahvaz, Iran, during the ۲۰۱۶-۲۰۱۷ growing seasons. The dust blew on the trees canopy using a blower and the leaf gas exchange was evaluated using an infrared gas analyzer on the intact leaves. After treatments, photosynthesis rate, transpiration rate, and stomatal conductance were measured. The leaf gas exchange results showed significant differences between the applied combined treatments on photosynthesis rate (from ۹.۱۸ to ۰.۶۴ μmol CO۲ m-۲s-۱), stomatal conductance (from ۳۹.۹ to ۶.۶۷ mmol m⁻²s⁻¹), and transpiration rate (from ۲.۷۸ to ۱.۴۹ mmol H۲O m-۲s-۱). Deposition manner of dust particles, the number of stomata in the abaxial and adaxial surfaces of leaflets, and the minimum dust-carrying capacity (MDCC) were determined using scanning electron microscopy (SEM). Stomata study using SEM showed that date palm leaflet surfaces are almost wavy and the stomata are situated in the concave surfaces in a linear arrangement on both abaxial and adaxial leaf surfaces. Although, there were no significant differences in stomatal density at the abaxial (۲۹۹ mm-۲) and adaxial (۳۰۰ mm-۲) leaf surfaces, the leaflet position within the leaf showed a significant influence on MDCC. The base positioned leaflets in the leaf showed the highest (۲.۵ mg cm-۲) and the upper positioned top leaflets showed the lowest MDCC (۱.۷ mg cm-۲), respectively. Also, SEM showed a sign of covering or entering dust particles into the stomata with possible stomata clog and blockage lead to the significant reduction of photosynthesis and crop yield. Besides, pollinated trees showed the maximum crop yield (۵۹.۱۷ Kg tree-۱), so the minimum yield was recorded on un-pollinated palm trees (۱.۹۰ Kg tree-۱).

Minimum dust-carrying capacity, Stomata blockage, Stomatal conductance, leaf abaxial and adaxial surface, Scanning electron microscopy.