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[Ref: PL Kelly et al: First report of a phytoplasma identified in coconut palms (_Cocos nucifera_) with lethal yellowing-like symptoms in Papua New Guinea. New Disease Reports (2011) 23, 9; [DOI:10.5197/j.2044-0588.2011.023.009] ———————————————————————— In October 2008, coconut plantations in the Bogia district of 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 neighbouring affected palms, and farmers have reported losses totaling over 5000 trees.
Apical buds of eight affected coconuts were collected and sent to the Global Plant Clinic for testing for phytoplasmas. 3 samples tested positive [by generic PCR]. For one of the amplicons, the partial 16S rDNA sequence showed that the LY-PNG phytoplasma matched most closely (96 percent) with members of group 16SrIV, Coconut lethal yellowing (CLY). In phylogenetic analysis 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). However, this is the 1st 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 USD 27 million and USD 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.
[Figure 1: Phylogenetic relationships between the LY-PNG phytoplasma, selected phytoplasmas of group 16SrIV, and other phytoplasmas; see at the source URL above.]