Similarities Between the Fungicidal Action of Isoprothiolane and Organophosphorus Thiolate Fungicides

Abstract

KATAGIRI, M., and Y. UESUGI. 1977. Similarities between the fungicidal action of isoprothiolane and organophosphorus thiolate fungicides. Phytopathology 67:1415-1417. A similarity in the mode of action of isoprothiolane and correlated cross resistance also were found between organophosphorus thiolate (PTL) fungicides in Pyricularia isoprothiolane and phosphoramidate (PA) compounds as in oryzae is suggested because cross resistance was found the case of the PTL fungicides and PA compounds. between them, and synergistic joint action and negatively Rice blast caused by Pyricularia oryzae is an important contained five 20 W fluorescent tubes (FL 20 BL), and the disease in Japan. Several types of fungicides are used to plates were placed about 40 cm below the tubes. control this disease. The organophosphorus thiolate Fungicides.--Samples of IBP, edifenphos, and (PTL) fungicides which includes compounds such as Sisoprothiolane were kindly supplied by Kumiai Chemical benzyl diisopropyl phosphorothiolate (IBP, Kitazin P, Industry Co., Ltd., Nihon Tokushu Noyaku Seizo K. K. Fig. 3) and edifenphos (ethyl S, S-diphenyl phosphorodiand Nihon Nohyaku Co., Ltd. respectively. Dihexyl Nthiolate, EDDP, Hinosan) are one major group used for methyl-N-phenylphosphoramidate (HPA) and dibutyl this purpose. N-methyl-N-phenylphosphoramidate (BPA) were preRecently another fungicide, isoprothiolane pared and purified as reported previously (3). (diisopropyl 1,3-dithiolan-2-ylidenemalonate, Fuji-One, Selection of isoprothiolane-resistant mutants.-Plates Fig. 3) was developed and brought into practical use for containing PSA amended with 100 /MM (29 g!g/ml) of control of rice blast. This paper deals with the cross isoprothiolane were inoculated uniformly with about 10' resistance of P. oryzae to PTL fungicides and isoprothiolane and with other similarities between these compounds such as negatively correlated cross resistance and synergism with N-alkyl-N-phenylphosphoramidate (PA) compounds. I 'I MATERIALS AND METHODS ! Test fungus and growth conditions.-Two wild-type tstrains of Pyricularia oryzae, Hoku-373 and Ken-6019, and PTL-resistant mutants, selected from these strains as - reported previously (2), were used throughout these experiments. Wild-type strains were transferred twice a year to potato sucrose agar (PSA) slants, whereas PTL.... _ resistant mutants were similarly transferred to PSA slants amended with 0.3 mM IBP. Tests were carried out at 27 C C D on PSA medium unless otherwise stated. Conidia of test % strains used in the selection of mutants resistant to isoprothiolane and in evaluation of fungitoxicity were u produced by the method previously reported (2); i.e., by placing a mycelial mat grown on a thin PSA plate onto another agar plate containing 0.2% yeast extract and 3% s soluble starch followed by 4 days irradiation with nearultraviolet light. Irradiations were performed with fluorescent black light with peak intensity at Fig. 1-(A to D). Four typicaljoint actions as demonstrated by approximately 360 nm. The irradiation chamber the crossed-paper technique. Paper strips impregnated with test fungicides are shown by solid lines and the resultant growthCopyright © 1977 The American Phytopathological Society, 3340 inhibitory zones are shown by dotted lines: A) independent Pilot Knob Road, St. Paul, MN 55121. All rights reserved, action, B) additive action, C) synergism, and D) antagonism.