The effects of Micro-Dusts on Severity of Rotting in Palm Fruit at the Pre-Harvest Stages

The occurrence of the micro-dusts phenomenon as a result of environmental changes as well as reduction of rainfall and drying of wetlands in the country have begun since two decades ago and are increasing every year. At the same time, as the micro-dusts phenomenon occurs, the probability of transmission of the pathogenic agents on various crop products, such as dates will cause significant damage, quality degradation and marketability of this fruit. This issue has a particular importance in the commercialization and export of dates specially for Medjool variety. During the years 2013-2015, sampling was done from infected fruit tissues of different growth stages of Medjool variety consist of Khalal, Kharak, Rotab and date which were exposed to dust and samples were cultured in potato dextrose agar (PAD) culture medium. After examining the samples, the relative frequency of the most prevalent fungi causing rotting was determined in the date fruit. The fungi Alternaria alternata, Aspergillus niger, A. phoenicis, Helminthosporium sp., Fusarium sp., and Rhizopus stolonifer were isolated and identified as agents of the fungal rot from fruits infected with dust. Results showed that under relatively humid conditions, exposure of palm fruit by micro-dusts will increase the severity of rotting damage by 8.53% and the fruit falling by 13.43%. Results also indicated that amount of fruit rotting affected by this phenomenon was higher during the Rotab stage and early stage of ripening compared to the late stages of fruit ripening. Therefore, it is recommended that the covering of fruit clusters should be carried out before the time that Kharak turns into Rotab, so that the palm fruit can be protected from damages caused by fungal agents of rotting and dust contamination.