First report of a phytoplasma identified in coconut palms (Cocos nucifera) with lethal yellowing-like symptoms in Papua New Guinea

In October 2008, coconut plantations in the villages of Tobenam, Pupun and Dugumor, located in the Bogia district of the Madang Province in Papua New Guinea (PNG), exhibited lethal yellowing-like symptoms in both newly planted and old palms. Symptoms started with premature nut fall, followed by leaf yellowing and collapse of the crown leading to the death of the plant. Inflorescence necrosis, a symptom frequently linked with lethal yellowing (LY), was absent. The disease spread rapidly from neighboring affected palms, and farmers have reported losses totaling over 5000 trees in the Bogia district.

Apical buds of eight affected coconuts were collected and sent to the Global Plant Clinic, UK, for testing using real-time PCR (TaqMan^®) and generic primers that target the phytoplasma 16S rDNA (Hodgetts et al., 2009). Three samples tested positive and were further analyzed using conventional nested PCR with universal 16S rRNA phytoplasma primers P1/P7-R16F2n/R2 (Deng & Hiruki, 1991; Schneider et al., 1995; Gundersen & Lee, 1996). All three samples yielded amplicons of expected size (~1250 bp). One of the amplicons was selected for purification and its partial 16S rDNA sequence was deposited in GenBank (Accession No. GQ227853). BLAST comparisons showed that the partial 16S rDNA sequence of the LY-PNG phytoplasma matched most closely (96%) with members of group 16SrIV, Coconut lethal yellowing (CLY). Phylogenetic analysis supported BLAST comparisons since the LY-PNG phytoplasma clustered as a single distinct branch related to group 16SrIV (Fig. 1). CLY has previously been reported from the Americas and Caribbean. Other closely related lethal yellowing-like diseases have also been recorded from West Africa (Nigeria, Ghana, Togo, Cameroon), East Africa (Tanzania, Kenya, Mozambique) and the Far East (Kalimantan, India, Sri Lanka, Indonesia and Malaysia) (Eden-Green, 1997). However, this is the first report of the presence of a lethal yellowing-like disease of coconut in Oceania. Coconut is a very important crop for the coastal and island regions of PNG with exports of copra and coconut oil bringing in US$27 million and US$43 million per year. The discovery of a LY phytoplasma has important implications for the coconut industry as the experience in Jamaica suggests that the disease is capable of destroying almost the entire population of susceptible palms (EPPO/CABI, 1997).