Abstract
Tricyclazole [Beam®, 5-methyl-1, 2, 4-triazolo (3, 4-b)-benzothiazole], a new systemic fungicide registered recently in Japan for the control of rice blast caused by Pyricularia oryzae Cav., hardly inhibited the mycelial growth, conidial germination and appressorial formation of P. oryzae at concentrations less than 125ppm, but it protected the plants almost completely from the disease by foliage application at as low as 10 to 20ppm. Rice seedlings in a seedling box 60×30×4cm were treated with tricyclazole through the soil at a dosage of 2.5g as 75% wettable powder per box one week before transplanting. They were satisfactorily protected from the infection for about one month after transplanting; tricyclazole content was estimated to be about 3 to 8ppm. The basic fraction of petroleum extracts from the treated rice leaves was found to have considerably high inhibitory action against the conidial germination of P. oryzae, although no tricyclazole was detected. These results suggest the possibility that an antifungal substance may be produced in leaves treated with tricyclazole.
