Acquired Tolerance to Blasticidin-S in Pyricularia oryzae

HWANG, B. K., and H. S. CHUNG. 1977. Acquired tolerance to Blasticidin-S in Pyricularia oryzae. Phytopathology 67: 421-424. Thirteen naturally-occurring isolates of Pyricularia oryzae transfers on fungicide-free media. Successive monoconidial varied in tolerance to Blasticidin-S [l-(1'-cytosinyl)-4-[L-3'cultures of Bu7 were genetically homogeneous for tolerance. amino-5-(l"-N-methylguanidino) valeryl amino]-1,2,3,4The tolerant isolate Bu7 sporulated more profusely and tetradeoxy-f3-D-erythro-hex-enuronic acid benzylaminoshowed a higher percentage of germination of conidia on benzene sulfonate]. Isolates tolerant to 500, 700, 900, and media with or without fungicide than did the parental isolate. 1,300 ug/ml of Blasticidin-S were obtained using ultraviolet The Blasticidin-S-tolerant isolate also was tolerant to the (UV) irradiation and a high concentration of Blasticidin-S. antibiotic, Kasugamin, but not to the organophosphorus Tolerance to Blasticidin-S was unstable in all isolates except fungicides, Hinosan and Kitazin. Isolate Bu7 was more Bu7, which was obtained from UV-irradiated conidia; that virulent on seedlings of some rice cultivars than was the isolate retained a high level of tolerance even after 20 parental isolate. Additional key words: rice blast, antibiotics. Rice blast, which is caused by Pyricularia oryzae to grow on a medium containing both fungicides. Cavara, is one of the most important limiting factors in Investigations on the genetic and physiologic aspects of rice production in rice-growing countries. Recently, the tolerance to Blasticidin-S, which might have occurred in agricultural antibiotics and organophosphorus nature, could lead to a better understanding of the fungicides were found to be very effective against rice mechanisms of tolerance development. This paper blast. The antifungal antibiotic, Blasticidin-S [1-( 1'reports on the tolerance of field isolates of P. oryzae to cytosinyl)-4[L-3'-amino-5(l"-N-methylguanidino) Blasticidin-S and on the genetic and physiologic valeryl amino]-l, 2, 3, 4-tetradeoxy-/3-D-erythro-hexcharacteristics of tolerant isolates originating from both enuronic acid benzylaminobenzene sulfonate], has been UV-irradiated and nonirradiated conidia. widely used for the control of rice blast in Asia. As Blasticidin-S becomes more extensively used, the MATERIALS AND METHODS development of tolerance to it in P. oryzae may pose a serious practical problem. Isolates of P. oryzae were collected from the rice blast Mutants of Ustilago hordei, tolerant to benomyl and nursery at the College of Agriculture, Seoul National carboxin, were induced by ultraviolet (UV) irradiation University, where no fungicides have been applied since and were used to study the genetic and physiologic in 1972. In preliminary experiments, a large number of aspects of tolerance in the fungus (1). Yamasaki et al. (10) pathogenic races were identified on the basis of the obtained copper-tolerant isolates of P. oryzae by repeated international set of differential host cultivars (9). Thirteen exposure of cultures to copper, although some cultures pathogenic races were selected for this study. failed to adapt to certain copper concentrations. Monoconidial cultures of each isolate were used Similarly, tolerance to Blasticidin-S has been observed in throughout. The isolates used (race designation in P. oryzae, whereas development of tolerance to phenylparentheses) were: 2A2 (ID-15), 2A10 (IC-31), 2A15 (IAmercury acetate was inconclusive (5, 8). 65), 3A1 (IH-1), 3A5 (IA-79), 3A12 (IA-95), 3A13 (lAThe lack of a sexual stage in P. oryzae limits the testing 109), 3AI4(IA-127), 3A17(IE-3), 3AI9(IG-1), 3A20(IAof the genetic aspects of fungicide tolerance by sexual 125), 3A25 (IC-19), and 3A29 (IF-3). crosses. Dutta and Garber (2) claimed a genetic origin of The principal antibiotic used was Blasticidin-S, tolerance to acriflavine and filipin in Colletotrichum formulated as an emulsifiable concentrate with 2% active lagenarium by observing that the tolerance was ingredient (2% EC). Fungicides tested for cross-resistance maintained even after serial transfers were made on included the antibiotic Kasugamin (kasugamycin) at 2% fungicide-free media, and that the heterokaryon was able BC; and two organophosphorus fungicides, namely Hinosan (O-ethyl-S-S-diphenyldithiophosphate) at 30% Copyright © 1977 The American Phytopathological Society, 3340 EC and Kitazin (O,O-diisopropyl-S-benzylthioPilot Knob Road, St. Paul, MN 55121. All rights reserved, phosphate) at 48% EC. The fungicides were added to