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 diseases of the coconut palm (Cocos nucifera) in eastern and western Africa were 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 stringency to DNAs from four coconut cultivars with lethal disease (LD) in Tanzania and from a solitary West African Tall coconut palm with symptoms of Awka disease in Nigeria. Neither probe hybridized to DNA of the LD-affected hybrid coconut PB121 or to DNA of symptomless palms. Conserved, mollicute-specific oligonucleotide sequences used for polymerase chain reactions (PCR) primed the amplification of near full-length MLO 16S rRNA genes from all decline-affected palms. No restriction fragment length polymorphisms were observed when rDNA amplified from both LY- and LD-affected coconut palms were singly digested with the restriction endonucleases AluI, BamHI, DraI, EcoRI, HpaI, HpaII, RsaI, and ScaI. Polymorphisms were evident after digestion of MLO rDNA with TaqI. These data establish the existence of genetic relationships between 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 identical pathogens.