Browsing by Author "Tymon, A."

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    Genetic diversity in the coconut lethal yellowing disease phytoplasmas of East Africa
    (1999) Mpunami, A.A.; Tymon, A.; Jones, P.; Dickinson, M.J.
    DNA primers, based on the ribosomal sequences of lethal yellowing-type disease (LYD) phytoplasmas, were used to analyse genetic variation within the lethal yellowing-type diseases of coconut in East Africa. Samples were collected from palms in Kenya, Mozambique and high, medium and low disease incidence areas of Tanzania. The mollicutespecific primer pair P1 and P6 amplified a 1·5 kbp product from all diseased palms and no product from symptomless palms, indicating that phytoplasmas were associated with all of these diseases. However, the Rohde forward and Rohde reverse primers (a second rRNA primer pair designed to detect East African LYD-associated phytoplasmas) only amplified products from Tanzanian and Kenyan diseased palms and not from those of Mozambique. Conversely, primers Ghana 813 and AK-SR, designed for specific detection of coconut-associated phytoplasmas in West Africa, amplified products only from the Mozambique palms, indicating that the phytoplasma associated with LYD in Mozambique is more closely related to those fromWest Africa. This was supported by restriction enzyme digestion of PCR products. DNA sequencing of PCR products from phytoplasmas within Tanzania revealed no detectable differences in the rDNA sequences of isolates from high, medium and low incidence areas.
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    Identification of potential vectors of the coconut lethal disease phytoplasma
    (2000) Mpunami, A.; Tymon, A.; Jones, P.; Dickinson, M.J.
    Lethal disease (LD) is a lethal yellowing-type disease of coconuts associated with phytoplasmas in Tanzania, but the insect vector for it has not yet been identified. In this study, the auchenorrynchous insects in LD-infected coconut fields were surveyed to determine potential vectors for the disease. No significant correlation was found between disease incidence and numbers of insects collected from the field, possibly reflecting the unknown incubation period for the disease. However, analysis of more than 5000 individual insects by the polymerase chain reaction (PCR), using LD-specific primers derived from the phytoplasma 16S rRNA gene, revealed PCR products of the correct size from eight individuals of Diastrombus mkurangai and four of Meenoplus spp. When digested with restriction endonucleases, fragments of the same size as the LD phytoplasma were obtained. No PCR products were detected in any of the other insect species tested. These results implicate D. mkurangai and Meenoplus spp. as probable vectors of the LD phytoplasma.