Variation in Sensitivity Among Anastomosis Groups of Rhizoctonia solani to the Antibiotic Gliotoxin

Abstract

Considerable variation in sensitivity to gliotoxin was found among anastomosis groups (AG) of Rhizoctonia solani. In broth culture, gliotoxin at 2 or 4 ppm was fungistatic to fungicidal toward the mycelium disks of AG-1 (sasakii), AG-2-1, AG-2-2, and AG-3. Isolates of AG-1 (microsclerotial [ms]), AG-4, and AG-5 were much less sensitive, requiring gliotoxin concentrations of 8 ppm for complete inhibition. Sclerotia of AG-1 (ms), AG-1 (sasakii), and AG-2-2 showed reduced viability after submersion in gliotoxin solutions of 20 and 40 ppm. Sclerotia of AG-3, AG-4, and AG-5 were much less sensitive. Linear growth of Rhizoctonia mycelium toward gliotoxin in wells cut in agar plates did not differ greatly among anastomosis groups, but growth was generally reduced compared with check treatments.