Abstract
Cochliobolus miyabeanus and Pyricularia oryzae, the casual agents of brown spot and blast disease of rice respectively, acquired tolerance to the fungicide Hinosan just by one exposure. The slope of dosage response curve of Hinosan for the adapted isolates was greater than that for the parent isolates. C. miyabeanus and P. oryzae, respectively, adapted to 11 and 33 times the ED50 value of Hinosan. The acquired tolerance to Hinosan in C, miyabeanus was not of a permanent nature and was lost of maintenance in fungicide-free medium, but that acquired tolerance of P. oryzae was totally retained. However, both fungi lost their sporulating capacity when transferred to fungicide-free media. The tolerant strain of C. miyabeanus exhibited cross-tolerance towards Polyoxin-D, Cycloheximide, Difolatan and Bayleton. The tolerant strain of C. miyabeanus lost its virulence to rice plants.
