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First report of strains related to the phytoplasma associated with Tanzanian Lethal Decline on Cocos nucifera on the western coast of Madagascar

Pilet F., Rakotoarisoa E., Rakotomalala M.R., Sisteron S., Razakamanana H.N., Rabemiafara L.. 2021. Plant Disease, 105 (12) : p. 4146.

DOI: 10.1094/PDIS-03-21-0623-PDN

Madagascar is a high diversity hotspot in the world, and palms are highly represented with nearly 200 endemic species (Rakotoarinivo et al., 2014). Coconut tree (Cocos nucifera) could have been introduced in Madagascar by Austronesians around AD 400 or 700 (Beaujard, 2011). Sporadic coconut trees showing very severe wilt were observed in 2016 in three localities of the western and northern coast of the island: Katsepy (Sample MG16-001), Antsohyhi (MG16-004 and MG16-005) and Ambaritsatrana (MG16-010). Symptoms correspond on a severe ascendant wilt of the leaves, associated with necrosis of the inflorescences and absence of nuts and death of all trees was confirmed eventually. We investigated the implication of phytoplasma because of the apparent similarity in the symptomatology with Coconut Lethal Yellowing Disease and Coconut Lethal Decline occurring in East Africa (Mpunami et al., 1999), and because the western coast of Madagascar faces the Mozambican channel only 400 km apart from areas along the East African coast where those two diseases occur. Symptomatic (n=4) and asymptomatic (n=6) coconut trees were sampled by stem drilling. DNA was extracted from sawdust samples using a modified CTAB protocol (Mpunami et al., 1999). A direct polymerase chain reaction (PCR) targeting the 16S rRNA gene plus Internal transcribed spacer with the P1-1T (AAGAGTTTGATCCTGGCTCAGGAT)/P7 primers (Schneider et al., 1998) amplified a product of about 1.8 kb for MG16-001 and MG16-005 samples only, while the four DNA extracts from symptomatic trees showed a 1.2 kb amplicon by nested PCR using R16F2n/R16R2 primer pairs in the second round (Lee et al., 1998). Amplification of the secA gene using the primer pair secAFor1/secARev3 (Hodgetts et al., 2008) was performed in a single round and gave a product of 850 bp exclusively for the symptomatic tree DNAs. All amplicons were double strand sequenced (Genewiz, UK). Corresponding high quality sequences were deposited in GenBank and submitted to

Mots-clés : maladie des plantes; pathologie végétale; flétrissement; cocos nucifera; phytoplasme; madagascar; jaunissement mortel

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