Studying the effects of dust on date palm (Phoenix dactylifera L.) pollination and fruit set

Date palm is grown extensively in the arid and semi-arid regions of the world. Its annual income decreased recently. Some factors could be involved in this reduction, and dust could be one of them. Dust loads on leaves decrease stomatal conductance, increase leaf temperature, and reduce photosynthetically active radiation by shading leaf surfaces. This study has been conducted on approximately 8-year-old date palm trees at the Date Palm and Tropical Fruits Research Center of Iran. The experiment was arranged as RCBD divided into 12 treatments into three replications into two growing seasons of 2014 and 2015 to evaluate the effect of combined treatments including dust (D), rain (R), and pollination (P) on fruit set, parthenocarpy, and fruit abscission. Based on results, rain immediately after pollination can wash away most of the pollen grains from stigma surfaces but some pollens are trapped by stigma papilla cells that lead to some fruit formation. It was found that when rain occurred before pollination, rain drops filled in some of the spaces between papilla cells and covered the flower and stigma surfaces; so inhibit the direct contact of some of the pollen grains to the stigma surfaces. Our results indicate that dust deposition significantly reduces the reproduction of date palm cultivar 'Sayer'. This study approved the formation of a blockage layer of dust on flower and stigma surfaces. This dust insulator layer formed on the stigmatic surface inhibited most of the pollen grains for direct contact to the stigmatic surface; thus decreased pollen tube germination and consequently led to fruit set reduction.