RELATION BETWEEN FUNGICIDES AND FLOWER ABORTION IN DISEASE-FREE SOYBEAN PLANTS: PHYSIOLOGICAL, REPRODUCTIVE AND PRODUCTION ASPECTS

Abstract

Fungicides are essential inputs to the profitability of soybean crops, and foliar spraying of these pesticides has significantly expanded in recent decades. However, in addition to controlling and eliminating diseases, these pesticides can interfere with the physiology, reproduction and productivity of disease-free plants. Thus, we aimed with this research to evaluate the effects of three commercial fungicides on the photosynthetic process, the viability of the pollen grain and the yield components of disease-free soybean plants, applied in the vegetative and/or reproductive phases of the crop. In the first experiment, disease-free soybean plants of the cultivar SYN 1378C, were treated in the pre-bloom (V8) and bloom (R1) stages of development, with the application of three commercial fungicides: cyproconazole 150 g L-1 + difenoconazole 250 g L-1 (CPZ + DFZ; 250 ml ha-1; no adjuvant); azoxystrobin 300 g Kg-1 + benzovindiflupyr 150 g Kg-1 (AZB + BZP; 200 g ha-1; Nimbus® adjuvant (Syngenta)); propiconazole 250 g L-1 + difenoconazole 250 g L-1 (PPZ + DFZ; 150 mL ha-1; no adjuvant). In parallel, a control treatment was carried out, without the application of fungicide. The study was carried out in independent duplicates, and each experiment was carried out in randomized blocks, with four replications. The characteristics of phytotoxicity, gas exchange and chlorophyll a fluorescence, pollen grain viability and germination, flower abortion and yield components were evaluated. A second experiment was carried out, using the same soybean cultivar, treated with the application of three other commercial fungicides: epoxiconazole 50 g L-1 + fluxapyroxade 50 g L-1 + pyraclostrobin 81 g L-1 (EPZ + FLX + PYR; 800 mL ha-1; Assist® adjuvant 500 mL ha-1 (BASF Ltda.)); trifloxystrobin 150 g L-1 + prothioconazole 175 g L-1 (TFX + PRZ; 400 mL ha-1; Aureo® adjuvant (Bayer Ltda.)); and trifloxystrobin 150 g L-1 + prothioconazole 175 g L-1 + bixafen 125 g L-1 (TFX + PRZ + BXF; 500 mL ha-1; Aureo® adjuvant (Bayer Ltda.)) and a control treatment without application of fungicide. The plants received one (in the R1 stage) two (in the R1 and R2 stages) or three (in the R1, R2 and R3 stages) fungicide applications. The experimental design was in a factorial scheme (4 treatments x 3 applications), in randomized blocks, with eight replications. In both experiments, the six fungicides evaluated did not affect gas exchange, pollen grain germination and crop yield. However, the fungicide EPZ + FLX + PYR negatively affected the photochemical characteristics of soybean plants, while TFX + PRZ reduced the number of soybean plant pods after one application, which may have reflected in a higher weight of one thousand grains as a form of compensation. The fungicides TFX + PRZ and TFX + PRZ + BXF affected the germination of soybean pollen in this study, but without changing the yield components of the soybean plants. The application of fungicides at different stages of development and different numbers of applications did not alter the metabolism and production of disease-free soybean plants under controlled conditions.