Aetiology, Economic Importance And Control Of Mango (Mangifera Indica L.) Tree Decline Disease In Northern Region
Date
2016-07
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University of Ghana
Abstract
This research was conducted from May, 2015 to July, 2016 in the three mango growing districts of the Northern Region of Ghana to obtain baseline information on farmers’ knowledge and perception on prevalence, spread, economic importance and control of mango tree decline disease; determine disease incidence and severity; identify the causal agent(s) of the disease and to develop a chemical control regime for management of the disease. Questionnaire survey and interviews were used to gather information from eighty-four (84) mango farmers selected at random in the three mango growing districts in the Northern Region of Ghana. Disease incidence was determined by counting both healthy and infected mango plant. Disease severity was determined across seven mango farms in each of the experimental communities using a 0 to 5 disease assessment key. Isolation of the causal organism(s) from advancing margins of diseased tissue was done first on Water Agar (WA) and sub-cultured onto a Potato Dextrose Agar (PDA). Identification was carried out using both morphological and molecular techniques. The pathogenicity of three fungal isolates were tested with an incision made on ten months old mango seedlings and mycelia plugs of each isolate inserted singly into the incision made on the stem. There were five mango seedlings per fungal isolate with control. Six fungicides with three levels were evaluated in vitro for their inhibitory effects on mycelial radial growth of the disease causal organism on Potato Dextrose Agar amended with three recommended rates of each fungicide in Completely Randomized Design with three replicates. Field evaluation of three fungicides selected from the in vitro trial was carried out in Randomized Complete Block Design with five plants per fungicide treatment with four replicates. Data was collected on disease incidence and severity before each fungicidal application at two (2) weeks intervals and vegetative growth of plants. The study revealed that, all the farmers (100%) were aware of the occurrence of the mango tree decline disease but were unable to identify the causal agent(s) as well as the agents for spread of the disease within and among farms. Again, mango farmers were replacing their infected mango trees with arable crops such as groundnut, maize, yam and cassava. Disease incidence was generally high in all the three mango growing districts: Karaga (77.9%), Savelugu-Naton (77.1%) and Kumbugu (63.9%). However, Savelugu Nanton municipality recorded the highest disease severity (2.57) followed by Karaga district (2.0) and then Kumbugu district (1.42). Disease symptoms such as necrosis of leaves on small branches, gum exudation, bark splitting, vascular discolouration as well as defoliation of leaves were observed during the field visits. The pathogen causing the disease in the study area was identified as Lasiodiplodia theobromae. During the pathogenicity test, L. theobromae produced characteristic symptoms of mango tree decline disease. All the fungicides evaluated during the in vitro trial completely inhibited mycelial radial growth of L. theobromae except for Sulphur 80. Application of urea fertilizer to boost tree growth alongside spraying of Carbendazim (50 g/15L water) at two weeks spraying interval was effective in controlling the disease. The study revealed that mango tree decline disease is prevalence in the three mango growing districts where the study was carried out.
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Description
Thesis (MPhil)
Keywords
Aetiology, Economic Importance, Control Of Mango, Tree, Disease