Diversity of fungi associated with mirid (Hemiptera: Miridae) feeding lesions and dieback disease of cocoa in Ghana

Abstract

Dieback disease causes heavy yield losses of cocoa in West Africa and for over a century, control strategies have involved insecticide use against mirids whose feeding punctures provide access for fungal infection. Information on the true identity of the causal pathogens is needed for enhanced understanding of the epidemiology of the disease and for development of integrated control strategies. So, the aim of the research was to address the role and identity of the different fungi associated with dieback disease of cocoa in Ghana. Fungal isolates were extracted from severely infected cocoa tissue from Ghana at Silwood Park Campus, Imperial College London during 2006-2009. Morphological characteristics comprised colour and shape of colonies and sizes of conidia. The genetic diversity was evaluated using the Qiagen DNeasy Plant Mini Kit protocol to extract genomic Deoxyribonucleic Acid (DNA) followed by Polymerase Chain Reaction (PCR) and sequencing of the Internal Transcribed Spacer (ITS) region of ribosomal DNA. The procedure confirmed the presence of 117 fungal isolates. The most frequently isolated genera were Fusarium (dominant) and Lasiodiplodia. The Fusarium isolates were identified as F. chlamydosporum, F. solani, F. oxysporum and F. proliferatum. The Lasiodiplodia isolates were identified as either L. pseudotheobromae or L. theobromae. Fusarium and two Lasiodiplodia species are the causal agents of dieback disease identified so far by the study. Contrary to known facts, Fusarium decemcellulare was not isolated from any of the infected wood tissues from Ghana. © 2011 Academic Journals Inc.