Measurement of Fungitoxicity using the Filter Paper Disk Method

Abstract

The main objective in using this method was to determine the concentration of each of some six important fungicides used in African Agricultural and Horticultural practices, but which lacked information on their action against isolates of Sarocladium species that was necessary to prevent the radial growth (mm) of these pathogenic fungi. In this study experiments involving the quantitative measurement of organism response to the toxic compounds were conducted. The method of bioassay used in this study did not distinguish between merely inhibiting the fungus growth, a fungistatic action, and the outright killing of it, a true fungicidal action. From studies on the effect of fungicide concentration on radial growth of two isolates of Sarocladium species, Difolatex, Ortho Difolatan, Benlate, Dithane M-45 and Calixin M (Tridemorph), in that order, were found effective at different concentrations in preventing the radial growth of S. attenuatum (I_3). The actions of Calixin M and Bordeaux mixture were, however, generally poor. In a similar test against S. oryzae (I4), Ortho Difolatan, Difolatex and Benlate, in that order, were the best three fungicides against this isolate. S. oryzae (I_4) was found to be more resistant to the fungicides tested than S. attenuatum (I_3). The results showed that the most economical and effective concentration of a given fungicide depended on (1) the fungus, (2) the fungicide, and (3) the fungus-fungicide combination. The two isolates did not rate the fungicides in the same order, suggesting inherent variation in the chemical behaviour, the two isolates, or both groups. From the filter paper disk method used to measure the fungitoxicity of these fungicides it was found that (1) Difolatex and Ortho Difolatan were the best two fungicides against the two isolates of Sarocladium species tested. (2) Considering the six fungicides tested, the isolates did not rate these chemicals in like order, suggesting that (a) the recommendation for the best chemical depends on the causal organism of the disease, and (b) careful identification of the causal pathogen is very important in a control programme that seriously considers the use of chemicals. The implications of these studies are two-fold: (1) farmers like those of the European Development Fund financed Upper Noun Valley Development Project headquartered at Ndop, Cameroon, who changed from cocoa and coffee to rice farming will already be familiar with these chemicals from their previous use for protection against the cocoa pod and coffee berry diseases, (2) the fungicides Difolatex and Ortho Difolatan may ^therefore be included in an integrated pest management (IPM) programme in the African rice farming systems for the control of important diseases like the grain discoloration and sheath rot caused by Sarocladium species.