Kaiza, Dominick Alfred2026-08-282026-08-281987https://www.suaire.sua.ac.tz/handle/20.500.14820/7926DissertationIn the Bagamoyo District,large coconut plantations were established as early as 1870 and the industry received a further impulse from German settlers in the 1930's. The first report on the occurrence of the lethal disease was in 1911. fit present the incidence of the disease is low. Coconut palms were planted in the Klsarawe and Rufiji Districts during three main periods. The first during the Arab rule mainly between 1070 and 1888, the second during the German administration (1891 - 1914 ) and the third and most important after the first World Wer. Although the lethal disease occurred probably as early as 1890, it made little impact on the two first plantings. However, serious outbreaks occurred in the 1940's when the post 192B groves came into bearing. The most important outbreak in the Kisaj»owe District was near Sanga-Sanga in 1941. The disease spread in eastern, then southern directions to Msonga and Magawa. It moved as well to the north across the* Luhute valley to Sotele and Binge. In both bisec­ tions the disease spread over a distance of approximately 40 kilometers during a period of 35 - 40 years. While this general direction of movement over an extended period of years was revealed by the survey, the spread did not occiir along an extended front and was often unpredictable. There was no apparent relation between the direction of spread of the disease and the prevailing winds although it spread faster through groves planted along open spaces like valleys or swamps. Similarly rampant spread of the lethal disease was reported from the Rufiji and Kilwa Districts. Outbreaks of the lethal disease were reported at various places along the coast of mainland Tanzania at various times from the 19th century onwards. Sometimes independent outbreaks occurred simultaneously. It is therefore impossible to recognize one or more sources from which the lethal disease originated. The disease has obviously been indigenous in the coastal areas of mainland Tanzania for a long time. Injection of both bearing and non-bearing diseased coconut palms with tetracycline-hydrochloride antibiotic resulted in remission of symptoms in test palms but only when injection was started in sufficiently early stages of disease. Total remission of symptoms was obtained in only one bearing palm, fill the other remitting palms showed delayed symptom development compared with their controls and succumbed later, The temporary symptom remitting bearing palms often produ­ ced new healthy inflorescences which blackened later. In non­ bearing palms, those which were injected in early stages of dise­ ase showed completely rnaffected spear leaves for a long time but nonetheless the palms collapsed later. Taken in conduction with the finding of MLO in diseased palms, these results support the concept of a MLC etiology for the lethal disease. Insect population studies at seven different lethal disease affected sites revealed that the insects occurring on ce­ conut palms in Tanzania are almost exclusively planthoppers (Fulgoroidea). Twenty-nine different species were identified at CAB Intitute of Entomology of which only seven were common at all sites.These seven species are the most likely candidates as the vectors of the agent causing the lethal disease. Seasonal peaks in the populations of several species were observed but they were neither clear nor consistent. No variety or hybrid was visited by consistently higher numbers of insects than any other. Removal of shade appeared to result in an incre- ase of insects on the palms* In transmission trials to find the vector of the lethal disease, only one test palm showed symptoms similar to those of the disease. However, the palm was observed in an advanced stage • and not sampled. This possible case of transmission needs confirmation.enEtiology historyCoconut palmLethal diseaseLarge coconut plantationsTanzaniaThesis