Date palm phytoplasma disease (Wijam) is an emerging economical threat to the production of dates in the western provenance of Saudi Arabia. Disease symptoms were first observed in Al-Madinah region in 2014; a total of 525 healthy and symptomatic samples were collected from 34 date palm cultivars, were analysed by PCR and dot-blot hybridization. Nested PCR (nPCR) and sequencing results confirmed the presence of 16S rDNA phytoplasma, scoring 98% similarity to the 16SrI phytoplasma. Hybridization results showed that 17.4% of the collected samples were positively infected, the highest percentage of infection was found in city farms, reaching up to 13.4%. Furthermore, 16 date palm cultivars did not show any infection, while the other 18 cultivars had different percentages of infectivity. This finding may partially explain the sudden decline of date production in Al-Madinah region and suggests an alert to investigate disease control management procedures.

As part of ongoing effort to assess genetic connectivity among populations of Tridacna maxima across the Red Sea, and aiming at unraveling the potential driving mechanism underlying the identified population genetic trend, we intended in this study to re-analyze population genetic structure and reconstruct the demographic history of the giant clam species across the Red Sea, by examining a COI-16S rDNA concatenated sequences dataset in a total of 159 specimens from thirteen locations covering the Northern, Central, and Southern parts of the Red Sea. The obtained results unveiled marked mitochondrial genetic heterogeneity, with lack of isolation by distance as a potential driver of the observed genetic differentiation, against a background of lack of population genetic structure within the examined populations of T. maxima. Possible explanations to this recorded trend have been overwhelmingly discussed. Furthermore, evidence of recent demographic and spatial expansion within the giant clam species, as inferred from the outcomes of neutrality tests and mismatch distribution analysis, associated with the shallow mitochondrial genealogy and high haplotype diversity opposed to weak nucleotide diversity, suggest the potential involvement of both historical and contemporary processes in shaping the observed pattern of population genetic structure. Overall, the information retrieved from the current study set out to gather important and valuable data on genetic diversity as well as pattern and level of genetic connectivity among populations of the endangered species T. maxima across the Red Sea coast, which will be necessary to draw management and conservation methods as well as genetic improvement program.