Resistência ao glifosato em biótipos de Digitaria insularis e nível de dano econômico em soja e milho

Abstract

The Digitaria insularis has been distinguished by glyphosate resistance, biological alterations, difficult control and also the damage caused to soybean and corn. Therefore, if there is a change in the biological factors that act as resistance mechanisms in resistant D. insularis populations, there may be a change in the of Economic Threshold Level of this biotype in soybean and safrinha corn crop. Given the above, the objective of this work was to evaluate the absorption and translocation of glyphosate herbicide, the accumulation of shikimic acid, the anatomical characteristics of the leaves and the Economic Threshold Level in soybean and safrinha corn of two populations of D. insularis (resistant and susceptible) collected in agricultural areas in Paraná state. First the test was performed to prove the resistance and the Resistance Factor (FR80). In the study of the absorption and translocation of glyphosate herbicide and the accumulation of shikimic acid, a randomized complete block design in a 2x9 factorial scheme with four replications was used. The first factor was D. insularis biotypes (resistant and susceptible) and the second factor was the time of herbicide contact with the leaves of D. insularis plants m-2 (0; 2; 4; 8; 12; 24, 36, 48 and 72 hours). To determine the absorption, the percentage of control of the plants was verified. Shikimic acid accumulation in D. insularis biotypes was determined on harvested leaves that did not receive spraying. For the Economic Threshold Level experiments on soybean and safrinha corn, a randomized complete block design was used, in a 2x5 factorial scheme, with four replications. The first factor corresponded to D. insularis biotypes (susceptible and resistant) and the second factor, the densities of 0; 7; 14; 28 and 56 D. insularis plants m-2. The preliminary test to confirm the degree of resistance of D. insularis biotypes indicated the resistance of the biotype collected at PUC Toledo - PR experimental station, with FR80 equal to 19.3. The control of the resistant biotype observed at 28 DAA was considered satisfactory (80%) when the herbicide remained for 48 hours in contact with the applied leaf. In the susceptible biotype, satisfactory control occurred after eight hours of herbicide contact with the leaf. In resistant biotype, shikimic acid accumulation increased by 1.8 times from 0 to 12 HAA. In the susceptible it was verified that the accumulation increased twice. There was no change in the Economic Threshold Level on soybean crop among glyphosate resistant and insects susceptible D. insularis biotypes. Considering the low cost of D. insularis control and the high selling price of soybean for the 2017/18 crop, it was possible to determine the Economic Threshold Level of 0.86 plants m-2 of D. insularis. In safrinha corn crop, Economic Threshold Levels were different for glyphosate resistant and susceptible D. insularis biotypes. The differences may have occurred mainly due to the environmental conditions verified between the evaluated years. Therefore, considering the average values of grains and control cost for the year 2017 the Economic Threshold Level was 17.4 and 22.9 plants m-2 of the resistant and susceptible biotype, respectively and in 2018 the Economic Threshold Level. It was 13.7 plants m-2 for the resistant biotype and 11.6 plants m-2 for the susceptible biotype.