A mitochondrial molecular marker of resistance to Bayoud disease in date palm

We have previously shown that two circular plasmid-like DNAs (the S and the R plasmids) can be found in the mitochondria of date palm (Phoenix dactyli fera L.), a dioecious monocotyledonous tree. The two plasmids differ essent ially by the absence, in the R plasmid, of a 109-bp DNA segment. Using 36 d ate palm varieties and employing a PCR-based approach, we show that the sim ultaneous presence of the R plasmid and absence of the S plasmid can be con sidered as a reliable molecular marker of resistance to a vascular wilt (Ba youd disease) caused by the fungus Fusarium oxysporum f. sp. albedinis. Con versely, the simultaneous presence of the S plasmid and absence of the R pl asmid is correlated to Bayoud disease susceptibility The availibility of th is diagnostic tool for plasmid characterization should subsequently allow s imple, rapid and efficient selection of Bayoud-resistant individuals from t he large number of date palms obtained by natural crosses which display goo d date quality.