COMPARATIVE INVESTIGATION OF MLOS ASSOCIATED WITH CARIBBEAN AND AFRICAN COCONUT LETHAL DECLINE DISEASES BY DNA HYBRIDIZATION AND PCR ASSAYS

Mycoplasmalike organisms (MLOs) associated with lethal decline disease s of the coconut palm (Cocos nucifera) in eastern and western Africa w ere detected by dot hybridizations using (P-32)dATP-labeled cloned DNA probes. Two probes, each consisting of a genomic DNA fragment of the palm lethal yellowing (LY) MLO from Florida, hybridized at moderate st ringency to DNAs from four coconut cultivars with lethal disease (LD) in Tanzania and from a solitary West African Tall coconut palm with sy mptoms of Awka disease in Nigeria. Neither probe hybridized to DNA of the LD-affected hybrid coconut PB121 or to DNA of symptomless palms. C onserved, mollicute-specific oligonucleotide sequences used for polyme rase chain reactions (PCR) primed the amplification of near full-lengt h MLO 16S rRNA genes from all decline-affected palms. No restriction f ragment length polymorphisms were observed when rDNA amplified from bo th LY- and LD-affected coconut palms were singly digested with the res triction endonucleases AluI, BamHI, DraI, EcoRI, HpaI, HpaII, RsaI, an d ScaI. Polymorphisms were evident after digestion of MLO rDNA with Ta qI. These data establish the existence of genetic relationships betwee n MLOs associated with coconut lethal decline diseases in the western Caribbean region and in Africa and provide further evidence indicating that the LY and LD MLOs, although very similar, are not genetically i dentical pathogens.