Coconut lethal yellowing phytoplasma disease in Mozambique
Sammanfattning: The coconut palm (Cocos nucifera) is a major cash crop that is widely grown in coastal tropical regions of the world, including Mozambique. Outbreaks of coconut lethal yellowing disease (CLYD) are threatening the industry and the livelihood of a large part of the Mozambican population. The aim of this thesis was to study different epidemiological aspects of CLYD in Mozambique. Phylogenetic analyses of the 16S and secA genes were performed on plant and insect samples collected from different agro-ecological zones of Mozambique and Tanzania. A socio-economic survey was conducted to assess the effect of farming practices on CLYD incidence in Mozambique. The results revealed a high diversity of phytoplasma species associated with CLYD in Mozambique, namely: ‘Candidatus Phytoplasma palmicola’ 16SrXXII-A, Tanzanian lethal disease (LD) phytoplasma 16SrIV-C and a novel strain closely related to ‘Ca. Phytoplasma pini’ 16SrXXI-A, which was found in a mixed infection with ‘Ca. Phytoplasma palmicola’. Population genetics analyses confirmed the observed high phytoplasma diversity associated with CLYD in Mozambique. The studies also revealed that ‘Ca. Phytoplasma palmicola’ and Tanzanian LD phytoplasma occur in both Mozambique and Tanzania. A search for alternate hosts revealed that the palm species Elaeis guineensis and Borassus aethiopum are alternate hosts of CLYD phytoplasma in Mozambique. Previously, the potential insect vector of CLYD in Mozambique was thought to be the Platacantha lutea bug; however, our findings suggest that the potential alternate vector is the planthopper Diostrombus mkurangai. Finally, the results revealed that farm age, the presence of other palm species on the coconut farm, type of coconut variety grown, root cut practices and intercropping all had a significant (P<0.05) effect on CLYD incidence. This research study has increased our knowledge of CLYD epidemiology in Mozambique, which should help with the development of a more sustainable CLYD management strategy.
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