The osmotic and matric water potential characteristics of Phytophthora cinnamomi and Alternaria tenuis, fungi of widely different tolerance to water stress, were evaluated using agar media of varying nutritional status and three texturally different soils. The water potential of the agar media was controlled osmotically with KCl or sucrose. For the osmotic soil system, soil water content was maintained approximately constant and the desired water potential range was achieved by adding KCl solutions of different concentrations to air‐dry soil samples at a level equivalent to the water content of the field moist soils; for the matric system, decreases in water potential were achieved by adding decreasing volumes of water to air‐dry soil according to the moisture retention characteristics of the soils. Fungal growth was determined by measuring changes in colony diameter with time.Osmotic water potentials for optimum fungal growth in agar and soil systems were similar to the water potentials for optimum growth in soils of matric‐controlled water potential. However, with decreasing water potential both fungi were much less tolerant to matric than to osmotic stress, emphasizing that fungal response to decreasing soil water cannot be explained solely on a water potential basis, but must include consideration also of changes in other water‐related soil properties such as solute transport. Fungal responses to matric and osmotic water potential differences were not related to soil texture.From a practical standpoint, the matric potentials at which growth extinction occurred were numerically one‐half to two‐thirds of the corresponding osmotic potentials at which growth ceased. If this relationship holds for other fungi and other soils, fungal growth responses to water potential obtained using simple agar systems of osmotic‐controlled water potential should provide useful approximations of the matric water potential relations of fungi in soil, thereby facilitating prediction of the maximum soil water potential range within which specific fungi may develop competitively in natural soils.

No abstract

The antibacterial activities and bioactive constituents of ethanolic and aqueous extract of parts of the tuber against ten (10) clinical pathogens were determined, using agar well diffusion and standard techniques respectively. The proximate profile of this tuber included moisture content, ash, crude protein, fat, fibre and carbohydrate with varying percentages. The tuber was recorded to contain higher amount of saponin with the average of 24 mg/g, followed by cardiac glycosides with 13.13 mg/g, terpenoid with 8.48 mg/g, flavonoids followed with 5.36 mg/g and tannin with 4.21 mg/g was the least among the bioactive ingredients. Except for Proteus vulgaris, Serratia liquefaciens, Micrococcus luteus, Bacillus cereus and Citrobacter freundii, other test isolates were susceptible to the effect of the ethanolic extract of the peel of D. bulbifera at 500 µg/ml. High inhibition zones (between 17 and 22 mm) were recorded against 80% of the test organisms at 1000 µg/ml, except for 15 mm zone recorded against Bacillus cereus. The MIC and MBC of extract of D. bulbifera ranged in respect to the parts from 125 µg/ml to 500 µg/ml; and 250 µg/ml to 1000 µg/ml for peels and bulbils respectively. Antibacterial activity of the ethanolic and aqueous extracts of the bulbils of D. bulbifera was however, not profound in this present study compared to that of the peel. This study therefore, affirmed that D. bulbifera is a novel source of bioactive compounds which do not only enhance the antibacterial properties, but also ascertain its health promoting qualities.

No abstract

Aquaculture, the process of raising aquatic animals in ponds, is gaining more attention in recent times. The feeding system is an important aspect of aquacultural practice. A simple, relatively inexpensive automatic fish feeder was designed, constructed and evaluated. The operation of the feeder does not require highly technical expertise. This paper reports the design considerations, materials used and the effectiveness of the device, based on analysis of manual feeding and automatic feeding. The main features of the device are: hopper (stainless steel), bi-directional motor, feed platform and electrical control box. The design was based on specific parameters which included capacity of culture tank, stocking density, fish biomass, diameter of the feed, angle of repose and bulk density (of the feed). The total cost of the device was 17,000 naira (approx. 106 U.S. dollars). The device was tested under two culture tanks (0.75 m 3 each) with 10 kg-33 juvenile cat fish (Clarias gariepinus) placed in each tank with one feeding automatically and the other, manually. The feeder evaluation was based on feed conversion ratio (FCR) and feeding efficiency (FE).The total average gain in weight per fish was higher in the automatic feeding (89.50 g) than in manual (78.50 g). An FE of 20.9% was obtained in the automatic feeding and 18.6% in manual, in relation to their FCRs. A t-test, conducted at 5% significance level, indicated a significant difference in the two feeding methods.