Agriculture and Horticulture

Biography

Biography: Oben Tom Tabi

Abstract

Banana and plantain are important staples and cash crops cultivated in West and Central Africa. Their production is constrained by diseases among which is dieback that is of increasing importance worldwide. Pathogens associated to this disease are yet to be investigated in West and Central Africa. Studies were carried out to determine the incidence and etiology of the disease on Musa in selected locations in West and Central Africa and also, to develop effective diagnostic tests for the associated organisms. Eighty-four leaf, stem and root samples of ‘Cavendish Williams’ (CW) banana plants showing typical symptoms of dieback (leaf chlorosis, cigar leaf, stunting, mosaic, pseudostem blackening, necrosis and vein thickening) were collected from experimental plots in Centre des Recherches Agricole (CRA), Cotonou, Republic of Benin; International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria and selected farms in the Western Highlands of Cameroon (WHC). They were indexed serologically in IITA, Ibadan, by Protein A antibody sandwich-enzyme-linked immunosorbent assay (PAS-ELISA), triple antibody sandwich-enzyme linked immunosorbent assay (TAS-ELISA) for all known Musa viruses that include Banana streak virus (BSV; genus, Badnavirus), Cucumber mosaic virus (CMV; genus Cucumovirus), Banana mild mosaic virus (BanMMV; genus, Potexvirus/ Foveavirus) and Banana bunch top virus (BBTV; genus Babuvirus). Polyclonal antibody used for BSV assay was that of a Nigerian isolate; CMV assay was that of a cowpea isolate; BanMMV and BBTV-1 and 10 were from J. E. Thomas, Australia. Further identification was by Polymerase chain reaction (PCR), biological assays and Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Also, pathogenic fungi and bacteria were isolated from same samples using potato dextrose agar and nutrient agar. Isolates were re-inoculated on CW banana to determine their pathogenicity. Out of the 84 samples collected, 33% tested positive for all the Musa viruses with 8.3%, 7.1% and 16.6% from CRA, IITA and WHC respectively. BSV and CMV occurred most frequently (11%) and BanMMV least with 3.3%. Mixed infection with two viruses was noticed in 5 out of the 84 samples. Isometric particles of 28nm-30nm were observed in sap that tested positive to CMV. It produced puckering and mosaic symptoms on Nicotiana occidentalis and had particles with molecular weight (MW), 29K. Sap that was positive to BSV did not produce symptoms on test plants but had MW 37K. For BBTV, it was 20K and 27K for BanMMV. Expected band size of 600bp was obtained on 1% agarose gel electrophoresis after running immunocapture-reverse transcriptase- polymerase chain reaction using CMV antibody for trapping and oligonucleotide primers specific for a 485 nucleotide sequence corresponding to the 3’ end coat protein and C-terminal non-coding region of RNA-3. That for BBTV was an amplicon of about 900bp using primer pair BT1F2.30/ BT1R13.30 reported by Hafner et al. (1997). Another isometric particle with mean size of 30nm and MW 54 was identified. Its yield was 1.2 mg/kg at A_260nm-A_280nm and ribonucleic acid content 62% on purifying 200g of leaf. Fusarium semitectum, F. oxysporium, F. lateritium, Botryodiplodia theobromae, Curvularia and Pseudomonas sp. were also isolated and identified from samples collected. Their frequency of occurrence was 50%, 37%, 21%, 16%, 13.3% and 13.3% respectively.