Variation in a molecular marker for resistance of Saudi date palm germplasm to Fusarium oxysporum f. sp. albedinis the causal agent of Bayoud disease

Fusarium oxysporum f. sp. albedinis (FOA) is a seed- and soil-borne vascular wilt pathogen that causes a very serious and destructive disease of date palm (Bayoud disease). FOA is not currently known to occur in Saudi Arabia, but the disease has been moving eastward from its origin in Morocco and Algeria. The main objective of this study was to evaluate Saudi Arabian date palm germplasm at the molecular level to assess the presence of R or S plasmid. We evaluated 711 trees representing 42 date palm varieties in Saudi Arabia with a mitochondrial molecular marker and sequenced 64 of the diagnostic PCR amplicons. Most of the trees (628/711) carried the R-plasmid which is associated with Bayoud resistance against FOA fungus. The other 83 trees carried the S-plasmid and are predicted to be susceptible. All amplifications from putatively resistant trees had the same DNA sequence. Moreover, the sequence of the Saudi resistance amplicon was identical to the sequence of Moroccan resistance DNA publically available in NCBI-GenBank database. All the sensitive trees from Saudi Arabia shared a common DNA sequence. This sequence differed from the Moroccan susceptible one at seven unique mutations including five single nucleotide polymorphisms (SNPs) and two insertion/deletion (indels) regions. The uniformity of the sequences means that the introduction of new germplasm to Saudi Arabia will be easily detected. The relatively high frequency of putative resistance means that if/when this disease enters the Kingdom that most trees should be resistant.