INCIDENCE AND SEVERITY OF FUNGAL AND COMMON VIRAL DISEASES OF SOME SOYBEAN LINES IN A DERIVED GUINEA SAVANNAH AGRO-ECOLOGY

Nigeria is the largest producer and consumer of soybean in Sub-Saharan Africa with a low yield of less than 1 ton per hectare. Plant diseases play a major role in yield reduction for the crop. The study was to investigate the incidence and severity of fungal and common viral diseases of some soybean lines and determine their effects on soybean yield. Nineteen newly developed soybean lines with two local checks were evaluated. Fungal isolates were identified using cultural and morphological characteristics while Antigen Coated Plate-Enzyme-Linked Immunosorbent Assay was used for detecting viruses. Data were subjected to Analysis of Variance and means were separated at P = 0.05 using Duncan’s Multiple Range Test. Eight fungi isolated from diseased soybean plants were Fusarium oxysporum, Choanephora infundibulifera, Colletotrichum gloeosporioides, Culvularia spp., Fusarium verticilloides, Aspergillus flavus, Lasiodiplodia theobromae and Pestalotia spp., while the common viral symptom on the field was mosaic and mottling. F. oxysporum recorded the highest frequency of occurrence of 40.91% and 22.30%, in both years. F. oxysporum and C. infundibulifera showed characteristics symptoms of blight when used for pathogenicity on both checks. The soybean lines differed significantly [P = 0.05] in disease incidence and severity for both fungi and viral diseases. All lines were positive for Cowpea mild mottle virus [CPMMV] in 2016. All the lines evaluated were moderately resistant to leaf blight disease. The study concluded that these lines were tolerant to all observable diseases occasioned by their abilities to produce higher grain yield compared with the local checks, despite the high disease incidence and severity.