Isolation and partial purification of toxin from colletotrichum falcatum: the causal agent of red rot in sugarcane

The red rot fungus (Colletotrichum falcatum) spores were isolated from infected stalk pieces of sugarcane and grown on Czapek Dox agar medium to obtain pure culture. Spores were obtained from the pure culture and grown in Czapec Dox liquid medium for further studies. It was observed that the fresh and dry weights of fungal mycellial mat significantly increased with time. In addition, fungal growth resulted in a significant change in the pH of the Czapec Dox growth medium over a period of 35 days and gradually increased from 6.5 in the control medium to 8.4. The fungal toxin was extracted from the growth medium and used to treat cell suspension of a red rot resistant sugarcane cultivar HSF-240. The maximum toxin was produced after 28 days of fungal growth in the growth medium which was ascertained by the dry weight of residue obtained from the ethyl actate fractions, as well as percent mortality of sugarcane cells in suspension. The LD50 value (50% cell mortality) of toxin in ethyl acetate (ETA) fraction was 22.03 days while in water it was 30 days. The fungal toxin extracted in ETA fractions was more effective than the one extracted in water. It was mainly due to high solubility and potency of the toxin in ETA than in water. In general, the maximum toxicity was noted at the 4th week (28 days) which decreased at 5th and 6th week of mycelial growth. (author)