First report on the molecular identification of the phytoplasma associated with a lethal yellowing-type disease of coconut palms in Cote d'Ivoire.
Lethal yellowing (LY)-type disease has quickly developed among coconut palms in the Grand-Lahou in Côte d'Ivoire, currently affecting more than 7 000 hectares. Symptoms include leaf yellowing starting in the old leaves quickly moving to the young ones, drying of spikelet progressing to blackening of the whole inflorescence, rotting of heart, immature fruit drop, and crown death of the palm after six months of initial symptoms appearance leaving a scenery of bare trunks, typically known as "telephone poles". Leaves, stems, roots, hearts and inflorescences of LY symptoms-bearing (17 samples) and symptomless (8 samples) coconut palms were collected and subjected to total DNA extraction. Total DNA extracted was used as a template for a nested PCR assay with universal primers that target the phytoplasma 16S rRNA gene, R16mF2/R1 for the first PCR reaction, and R16F2n/R2 for the nested reaction. Samples that yielded R16F2n/R2 amplicons (7/17) were purified, cloned and sequenced. No PCR amplicons were obtained from symptomless coconut plants. Phytoplasma R16F2n/R16R2 sequences shared 100% sequence identity with each other. The consensus sequence (GenBank Accession No. KC999037) exhibited 99% sequence identity with phytoplasma members of group 16SrIV with the highest score for the CSPW phytoplasma from Ghana (JQ868442). Phylogenetic analysis based on the 16S rDNA sequence supported the grouping of the Côte d'Ivoire lethal yellowing phytoplasma (CILY) within the LY cluster, closely related to the Ghanaian CSPW strain. Earlier reports in Côte d'Ivoire refer to the presence of formerly called mycoplasma-like organisms in coconut affected with blast, the main nursery disease of oil palm in Africa. However, there have been no previous official records of LY-type disease, or its association with phytoplasma or bacteria-like pathogens.