The toxic effect of fernasan (containing 25 % thiram) was tested on Rhizoctonia solani and Fusarium solani in liquid and agar media. The fungicide was more effective in liquid (at 100 p.p.m.) than in solid media, where 400 p.p,m. checked the growth of R. solani, but was ineffective against F. solani. Both fungi exhibited a zone of inversion growth in liquid culture whereby certain intermediate concentrations were less inhibitory than lower or subsequently higher doses. Similar reaction was recorded for F. solani alone in fungicide-containing agar media. Sclerotimn formation by R. solani was highly significant, in relation to controls, at 40 p.p.m. The abundance of chlamydospores of F. solani was coupled with cessation of conidium formation with increasing fernasan doses.
effective. Vaartaja (1954), on the other hand, described the influence as 'outstanding giving good protection at widely varying concentrations' against R. solani and Pythium. Later, in 1960, he reported the suppression of R. solani, F. solani (Mart). Sacc. and Rhizopus stolonifer (Fr.) Linder by low concentrations of thiram. Rushdi & Jeffers (1955) found that 20 p.p.m, arasan (50 % thiram) completely inhibited R. solani in liquid media.
The purpose of the present work was to examine the effect of femasan upon two common soil-borne pathogens in the Sudan, namely R. solani and F. solani, in culture media for their degree of tolerence to fernasan and its impact upon mycelial and propagule development. Also the probability of detecting virulent strains that might resist future seed-dressing treatments with fernasan was evaluated.