Production Of Rhizoctonia Solani Toxin And Relationship Between The Toxin And Its Virulence

the crude toxin of Rhizoctonia solani in improved Richard's medium was extracted when the cultured filtrate was absorbed by active carbon with methanol as eluant and then the methanol was evaporated by rotavapor. The biological activity assay of the crude toxin showed that it could induce the characteristic symptom of rice sheath blight and inhibit the growth of rice radicle and make the seedling wilting. The experimental results revealed that the higher the concentration was, the more virulent the crude toxin was. When the crude toxin was 200 times diluted, it still had some biological activity.The culture condition for the production of Rhizoctonia solani toxin was studied. It was appropriate for the toxin production as follows: The optimum medium was improved Richard's medium, in which pH value was 7. The strains was cultured for15-20 days at 25~30℃, with darkness and shake in hand two times every day.It was found that the ability of toxin production was obviously different among the isolates. There was a significantly positive correlation between the ability of toxin production and the virulence of R. solani with r value of 0.8255, which indicated that the toxin of R. solani played an important role in the infection process.The seeds of rice varieties with different resistances were treated with the crude toxinof R. solani. It was found that the radicles of resistant rice varieties (TEQIN and J-85) were more tolerant to the toxin than those of the susceptible variety (LMNT). The seeds of LMNT could not nearly germinate and its leaves became curling and wilting after the treatment of R. solani toxin. So the resistances of rice varieties could be primarily identified by the treatment of rice radicles and seedlings with the crude toxin of R. solani.The inoculation tests showed that all isolates of R. solani and R. cerealis and their crude toxins had virulence on the plants of rice, maize and wheat. R. solani and its crude toxin was more virulent on rice and maize than R. cerealis and its crude toxin. On the contrary, R. cerealis and its crude toxin was more virulent on wheat than R. solani and its crude toxin.