Inoculation and disease assessment of rice blast. An isolate of M. oryzae, Naga 69-150, virulent to Akitakomachi, was used for inoculation. For inoculum preparation, the isolate was grown on oat meal agar in petri dishes at 25°C. After mycelial mats had covered the surface of the agar plates, the mats were brushed gently with a toothbrush and then exposed to black light blue fluorescent lamps (FL20S BL-B; Hitachi) for 2 days. The surface then was washed with sterilized distilled water and filtered through two layers of tissue paper to prepare the conidial suspension. The conidial concentration was adjusted to approximately 5 × 105 conidia ml–1 and Tween 20 was added to a final concentration of 0.02% (vol/vol). Six hills of rice plants in each plot were covered with a transparent polyethylene film with a thickness of 0.07 mm and immediately inoculated with the rice blast fungus in the field just before sunset by spraying 20 ml of the conidial suspension per hill. Polyethylene film was removed just before sunrise of the next day. The film blocked wind and kept moisture inside while