Effects of Ethrel and auxin applications on date palm fruit abscission during development

Abstract

'Medjoul' is a large semidry date cultivar that is marketed as a special elite product. Fruit size and quality are determined by fruit load, which is dependent on the level of fruit set, fruitlet thinning protocols and natural drop. Currently there is no information on the process of natural fruit abscission in date palms and specifically not on abscission of 'Medjoul'. In the present study abscission levels were characterized through fruit development in vivo and in vitro. Fruit abscise throughout development. During two stages, at an 'Early fruitlet drop' and a 'June drop' (at 25–45 and 80–100 days after pollination respectively), specifically high rates of abscission were observed. The level of fruit set and the fruit load affects these two peaks respectively. Ethrel treatment, an ethylene releasing chemical, significantly induced fruitlet drop while Auxin (2,4-D) treatment reduced the rate of natural fruit drop in vitro, especially during the developmental stages with high natural abscission. A specific abscission zone located at the base of the fruit, just between the calyx and spikelet was detected. Following Ethrel treatment, breaks and cracks in this tissue were detected. This data will enable better understanding of fruitlet and fruit abscission in date palm, which is extremely important for a high quality production of 'Medjoul' dates.