Symptomless Effects of Experimental Fungicides on Wheat

Abstract

The experimental systemic rust fungicide, Hoe-6052, was 3050 F did not. Hoe-6052 also affected the photosynthesis of previously found to reduce the yield of a wheat rustwheat quite appreciably, while EL-273 and BAS-3050 F did resistant cultivar, and not to increase the yield of a susceptible not. It is suggested that tests like those of photosynthesis and cultivar, even though it controlled the rust. This compound, respiration be included at an early stage of development of as well as EL-273 affected the respiration of the wheat fungicides. cultivar F.A. 8193, while the experimental fungicide BASPhytopathology 64:812-813. Additional key words: photosynthesis, deleterious effects of fungicides. A recent development in pesticide science is the translocation of these fungicides, they are distributed introduction of systemic fungicides, i.e. chemicals highly acropetally in the various parts of the plant and thus toxic to the fungi which cause plant diseases, that are result in a long-term protection against plant diseases (1). translocated readily in higher plants. Due to It is obvious that only chemicals which are not phytotoxic to the host plant can serve as fungicides. Therefore, lack of phytotoxicity to agricultural crops is an essential z-I100 characteristic when chemicals are tested for their 0 potential use as fungicides. However, phytotoxic action I80 of pesticides is usually determined by visual symptoms zE 80 such as growth, stunting, deformations, chlorosis, necrosis, turgor decline, etc. Limited information is 6 0 available at present, on subphytotoxic effects of fungicides on plants (7), and tests for such effects are usually not included in screening programs of new 40 /-pesticides. -, We report here that some experimental fungicides for 020 the control of cereal rusts may harm the host plants by interfering with the respiration and/or photosynthesis. They might cause an invisible damage to the crop, in spite 0 of the fact that the rust is effectively controlled. 7.5 75 750 The experimental systemic fungicides tested were: 2CONCENTRATION OF Hoe-6052 [kg/mi] methyl-5,6-dihydro-4-H-pyran-3-carbonoxide anilide (Hoe-6052, 75% a.i., supplied by Farbwerke Hoechst Fig. I. The effect of Hoe-6052 on the rate of photosynthesis at AG); 0-methyl benzoic acid anilide (BAS-3050 F, 75% 21 C in detached leaves of F.A. 8193 wheat. Leaf segments a.i., supplied by Badische Anilin & Soda Fabrik AG); immersed for I h in suspension of different concns of Hoe-6052, d ai. sple b disch Io in y & Sa F AG); washed, and then tested. and oa-(2,4-dichlorophenyl)-oa-phenyl-5pyrimidinemethanol (EL-273, 4% a.i., supplied by Eli Lilly). In a previous work (6) it was found that under 0 glasshouse conditions, Hoe-6052 showed promising S1 046 results in controlling leaf and rusts of wheat. It was |l •,t • 1177 a-also found under field conditions, that in the cultivar N80oFxA o -------46, which is susceptible to rust, several of the z 750,po 9/mi 15 ,mg/ml treatments yielded less than the check plots, despite an 60 ] 7 appreciable control of the rust. In addition, it was -found that the same fungicide reduced the yield of the 40 stem rust-resistant cultivar H-1 177. These results pointed out an adverse effect of Hoe-6052 on wheat, an effect of such magnitude that it even seemed to negate the 20 -, ----.--beneficial effect of rust control. These findings led us to test possible reasons for the deleterious effect of the Hoe6052, and to compare it to other fungicides. 2 4 6 8 10 DAYS AFTER TREATMENTS We checked the effects of Hoe-6052, BAS-3050 F, and Fig. 2. The effect of Hoe-6052 on the rate of photosynthesis in EL-273 on respiration and on photosynthesis of first detached leaves of three wheat cultivars. Attached leaves were leaves of wheat cultivar F.A. 8193. The effect of H-6052 dipped in suspension of 750 and 1,500 pg/ ml ofthe fungicide and on photosynthesis was also checked on cultivars N-46, tested later at different intervals at 21 C. and H-1 177, respectively, the susceptible and resistant