Effect of Long-Term Storage on Pollen Reproductive Quality and Polyphenolic Content of Date Palm (Phœnix dactylifera L.) Species in Tunisia

Knowledge of the level of the storage effect on the viability, germination capacity and the bioactive components of date palm pollen is important to identify the best conditions that can maintain its agronomic and medicinal properties for long-term preservation. In this context, the present work aimed to evaluate the effect of long-term storage on the pollen reproductive quality and the total polyphenol content of date palm pollen. Pollen of 24 male genotypes was collected for 3 successive years from 2017 to 2019 and stored at +4 °C. Alexander staining and in vitro germination were used to estimate pollen reproductive quality. The polyphenolic compounds were determined using the Folin–Ciocalteu method. The results showed that viability displayed a variation between the fresh and the stored pollen with a difference of 13.19, 8.11 and 3.96% for 2017, 2018 and 2019, respectively. Indeed, some male genotypes were characterized by the conservation of their pollen viability throughout the storage period. Moreover, analysis of variance (ANOVA) revealed a significant difference of pollen germination before and after storage. The acetone extracts recorded the highest content of total polyphenols with values varying between 11.37 and 19.43 mg GAE/L. The ANOVA showed that the polyphenol content of pollen date palm did not differ after storage time. The present study permitted a validation of the change of date palm pollen performance under +4 °C storage with high stability of its phytochemical properties. Overall, these results demonstrated that the storage method at the +4 °C temperature is very useful to maintain the bioactive compounds of date palm pollen. The results of the present study suggest that date palm pollen could be efficiently maintained at +4 °C for medicinal use and could be further used for breeding purposes.