Sex-Differentiation Based on Fluorescence In Situ Hybridization (FISH) with 5s and 45s rDNA of Egyptian Date Palm Trees

The date palm (Phoenix dactylifera L.), 2n=36, is a dioecious long-lived monocotyledonous plant, which belongs to the family Arecaceae. It is one of the excellent candidate crops in arid and semiarid regions of the world. Recently, fluorescence in situ hybridization (FISH) has become a powerful and useful tool for the direct detection of specific DNA fragments in the genome. In this technique, ribosomal DNA genes (45S and 5S rDNA) are commonly used as markers for the physical mapping of plant chromosomes to analyze genomic organization. To date, there is no report on rDNA loci in Phoenix dactylifera detected by FISH. The objective of this study was to develop a sex-specific fluorescence in situ hybridization (FISH) markers with 5S and 45S rDNA in Egyptian Date Palm Trees (cv. Zaghloul and Siwi). The results successfully revealed clear differences between males and females belonging to both cv. Zaghloul and Siwi by using 45S rDNA FISH. The fluorescence in situ hybridization (FISH) with 45S rDNA localized two clear telomeric intermediate-signals in female palm trees belonging to cv. Zaghloul and Siwi. While, it exhibited three clear telomeric intermediate-signals in male trees belonging to cv. Zaghloul and Siwi. On the other hand, results of fluorescence in situ hybridization (FISH) with 5S rDNA didn’t reveal any clear differences between males and females belonging to cv. Siwi. Based on the above results, we hypothesize that the third signal (unpaired signal) of 45S rDNA probe characterized in both Siwi and Zaghloul males is located on a male chromosome (Y chromosome). This finding can be utilized and used as cytological marker to differentiate between male and female trees in Egyptian date palm at an early stage.