Culture filtrates of 13 isolates of Macrophomina phaseolina, the causal of charcoal rot of soybean differing in their pathogenicity, differed in the effect on seed germination and length of radical roots.
Cut soybean seedlings immersed in un-autoclaved and undiluted crude culture filtrates of the different isolates showed necrosis m stem and leaf tissues commenoed as small brown necrotic speck's (N) which first appeared on the lowest leaves.
Unautoclaved as well as autoclaved culture filtrates isolates induced symptoms in cut seedlings similar to those produced on potted plants artificially inoculated with the different isolates. Symptoms induced by autoclaved filtrates appeared later and their progress was lower as compared to those induced by the autoclaved ones. Toxin(s) from culture filtrates and extracts from inoculated seedlings were dialyzable, insoluble in organic solvent soluble in water and heat stable.
The highly pathogenic isolate was highly productive of toxin(s) and yielded 935mg/liter of culture filtrate, while the least pathogenic isolate was least productive of toxin(s) (380 mg/litre).
Five distinct bands were observed for the different components of the gel. The Rf values of these bands were 0.30, 0.37, 0.47, 0.85 and 1.0 indicating differences between the components of the toxin(s). Cut seedlings immersed in different concentrations of the toxin(s) showed necrosis in the leaf tissues first appeared in the lower-most leveas, as small increased with increasing the concentration of toxin(s) and time of immersion.