Organic amendment tested in the present experiment against Sclerotium rolfsii were mustered oil cake, sawdust and rice husk. Each of them was used @ 30,40,50,60, and 70g/1 of potato dextrose agar (PDA). The medium was prepared by mixing water extract of 200g potato slice, 15g dextrose and 20g agar per liter. It was autoclaved at 121° C temperature under lkg/cm2 pressure for 20 minutes, Tuite (1969). The organic amendments tested in the present study were mustered oil cake (MOC), saw dust (SD) and rice husk (RH). A mixture of rice husk and mustered oil cake were also used in combination. All of the materials were used @ 30, 40, 50, 60 and 70 g/liter of the basic medium. Water agar (1.5%) was used as basic medium. A pathogenic strain of S. rolfsii was isolated from stem and root rot infected root of cotton following tissue planting (Tuite, 1969). It was multiplied potato dextrose agar medium in petridishes. The water agar (WA) at 15g/liter and PDA (200 g peeled potato, 20g dextrose 17g agar/liter of water) were prepared following standard procedure (Anonymous, 1968; Tuite, 1969). Poison food technique was followed for testing the organic materials (Grover and Moor, 1962). To prepare inocula of S. rolfsii, the fungus was grown on PDA. Mycelial block was cut from a 3 days old culture using a 5mm cork borer. The blocks were uses as inocula.
Water extract of each of the materials was used for testing their efficacy to inhibit mycelial growth. To prepare water extract 30, 40, 50, 60and 70g of mustered oil cake, saw dust, and rice husk were soaked in water separately for 24 hours. At the end of the soaking period, each of the materials was filter through whatmann-2 filter paper. The residues were discarded and the filtrates were used as extracts. To prepare water extracts mustered oil cake and saw dust, 10, 20, 30, 40, and 50g of sawdust taken in 1500m1 beaker containing 1000m1 water. Mustered oil cake was added to the beakers @20g per beaker. Two materials were thoroughly mixed and soaked for 24 hour. Water extract of the mixture was taken after filtration. Agar was added to each of the extract at 15g/1000m1 of the mixture were cooked until melting of the agar and autoclaved at 121° C under lkg/cm2 pressure for 20 minutes. Melted amended extract agar was poured into 90mm glass petridishes at 20m1/dish. Plates of water agar plates used for control treatment. The plates were inoculated with 5mm mycelial disk of S. rolfsii cut from 3 days old PDA culture. The inoculated petridishes were incubated in an incubator at 26± 2° C for 4 days.
Measurement of radial mycelial growth After 4 days of incubation, radial mycelial growth (mm) of Sclerotium rolfsii in petridishes was recorded. Radial growth (mm) was measured by taking average of two diameters taken at right angles for each colony. The plates were kept in the incubator for 15 days for sclerotia formation. Inhibition of radial mycelial growth was computed based on colony diameter on control plate using a standard formula.
% Inhibition =( x - y / x) x 100
Where, x = Average growth (mm) of S. rolfsii in control petridishes y = Average growth (mm) of S. rolfsii on amended extract agar.
After 15 days of incubation numbers of sclerotia produced in each petridishes were counted manually. The data were analyzed statistically for ANOVA using MSTAT-C computer program. The means were compared by Duncan's Multiple Range Test (DMRT) at 1.0% probability level.