Studies on the Leaf Spot Disease of Celosia Argentea Linn ('Soko") In Nigeria
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The leaf spot disease of Celosia argentea Linn was first observed by the present worker, in April 1973, in the horticultural section of the Lagos State Ministry of Agriculture and Natural Resources farm at Agege. It was shown to be caused by Fusarium lateritium Nees. The disease was reproduced by artificial inoculation in greenhouse experiments and also on hosts grew in soil from which the fungus had been isolated. The disease was observed on the host collected from various other localities in South West Nigeria. The fungus produced both leaf and stem spots. Symptoms appeared on seedlings but became more severe as the plant matured. Mycelial growth of the fungus was best on Czaoek Dox agar made up with the host extract (CDAE). Sporulation of the pathogen occurred under certain conditions and on some media. Cardinal temperatures for radial growth and sporulation were 200 and 250C. Spores of the pathogen - Fusarium Lateritium showed tolerance to changes in relative humidity but could not withstand exposure to high temperatures. The perfect stage of the pathogen was obtained by a cross of different strains of the pathogen. Sections of diseased leaves showed that the pathogen hyphae ramify the epidermal cells of host leaves growing both inter and intracellularly. Biochemical analysis of the diseased and healthy leaves showed relatively higher concentrations of carbohydrates and proteins in diseased leaves than in healthy leaves.