No abstract

The incidence and severity of the Rice Yellow Mottle Virus (RYMV) was monitored in various rice environments in West Africa. Its presence or absence being determinded through symptomatology and serological tests. RYMV was found in all the rice growing environments at different levels of incidence and severity which appear to be dependent on the type of variety planted, the rice environment and the climatic factors under which the rice is cropped. RYMV has been shown to cause losses ranging from 19.5% to 95.5%. Graminaceous weeds including some wild rices have been confirmed as alternate hosts for RYMV. Twenty five rice cultivars consisting of local and locally developed cultivars showed tolerant reactions to RYMV. Most of these varieties showed stable resistance to rice blast in an earlier study. The manifestation of RYMV symptoms on the uninoculated test rice varieties indicated the possibility of the virus being transmitted either through the virus vector or might be seedborne.

The ability of Pyricularia oryzae to grow and sporulate under various artificial environmental conditions was investigated. The pathogen grew best on Potato Dextrose Agar and sporulated best on one percent Soluble Starch Yeast Extract Agar. Ammonium chloride medium as nitrogen source favoured its growth and conidia production. The pathogen utilized xylose, arabinose, starch, glucose and inulin for growth and conidia production. The minimum, optimum and maximum temperatures for growth and conidia production were 10°, 25° and 37°C. The humidity treatment increased conidia production from 8.0 × 103 to 18.4 × 103 conidia/ml. The optimal pH range for growth was 5.5–10.5 and 5.5–7.0 for conidia production. Exposing cultures to continuous artificial illumination enhanced conidia production.

The occurrence of dermatomycoses and the in-vitro therapeutic efficacy of some antifungal agents on dermatomycotic organisms were investigated. Of the 550 primary school children screened, the incidence was one hundred (18%), 70 were males (representing 20% of the males screened) and 30 females (15% of the females sampled). The differences between male and female prevalence were insignificant. Three species of dermatophytes were isolated and identified. These were Microsporum canis, Trichophyton tonsurans and Epidermophyton floccosum. The antifungal agents tested on E. floccosum were griseofulvin, terbinafine and ketoconazole. They produced different sized zones of inhibition against the growth of E. floccosum. Griseofulvin exhibited a 50% inhibition of growth on E. floccosum at 63.00 mg/L. Terbinafine on the other hand exhibited varying levels of inhibition of growth at varying concentrations, at 0.07 mg/L, terbinafine achieved 46% inhibition of growth on E. floccosum. The drug achieved 100% inhibition of growth on the isolate at 61.81 mg/L. In the case of ketoconazole, 50% inhibition of growth was achieved at 100 mg/L while 100% inhibition of growth was achieved at 200 mg/L. The antifungal effects of the three drugs were confirmed by broth dilution tests where terbinafine was found to be fungistatic on the growth of E. floccosum at concentrations ranging from 0.013-1.700 mg/L and was fungicidal at concentrations ranging from 0.027-1.700 mg/L. Ketoconazole was found to inhibit the growth of E. floccosum at 0.003-1.700 mg/L and was fungicidal at concentrations ranging from 0.027-1.700 mg/L. It however did not succeed in killing the isolate under the same range of concentrations. Griseofulvin exhibited fungistatic effects on the growth of E. floccusum at 0.013-1.700 mg/L. In conclusion, ketoconazole and griseofulvin were found to be fungistatic and not fungicidal while terbinafine was both fungistatic and fungicidal on the pathogen. Terbinafine was found to be the most effective drug in inhibiting E. floccosum.