Controle de plantas daninhas e seletividade a culturas pela aplicação de isolados fúngicos

Abstract

The incorrect use of herbicides for the control of weeds has caused several environmental problems and the emergence of species resistant to several mechanisms of action. In this sense, bioherbicides stand out as an alternative to conventional control. In this work, we collected systematic weeds that showed symptoms of diseases caused by fungi. The collected samples were taken to the agroecology laboratory of UFFS - Erechim campus where the parts of the plants that presented disease symptoms were isolated in BDA culture medium to develop the possible microorganism. Afterwards, successive repetitions were carried out until obtaining pure cultures. Once the pure cultures were obtained, they were grown in Shaker at 28 °C and 120 rpm, remaining in these conditions for three days. Then the fermented was removed from the Shaker, sieved and allocated in spray cans until the moment of application. The obtained microorganisms were submitted to Screening to evaluate the cultures with phytotoxic potential. The test plants chosen were papaya (Urochloa plantaginea), dairy (Euphorbia heterophylla), black pickle (Bidens pilosa) and buva (Conyza bonariensis). The design was completely randomized with 3 replicates. The evaluations were visual, being attributed notes of injury on the weed leaves. After the preliminary tests were selected three fungi that presented greater phytotoxic potential and were used in later tests. For the later tests the same experimental design of the Screening was used, however with the addition of Aureus adjuvant to the extracts. The extracts were also applied on the soy, beans and corn cultures in order to verify the selectivity to cultures. The three selected microorganisms were identified as Fusarium oxysporum, F. ploriferatum and Trichoderma koningiopsis. The extracts obtained from these microorganisms were submitted to enzymatic activity analysis of cellulase, lipase, peroxidase and amylase. Among the test plants, the most sensitive to the biological control was the milkman, presenting symptoms for the three selected microorganisms. Among the microorganisms, T. koningiopsis showed the most effect on dairy plants, and also showed the highest activity for cellulase and lipase, showing values of 11.455 and 9.84 U/mL, respectively. The observed symptoms were foliar necrosis, in addition to shading and chlorosis. From the tests performed, the microorganism T. koningiopsis stands out with the highest phytotoxicity scores on the milkman, up to 60% in the highest doses with addition of adjuvant and should be submitted to further tests to confirm the results observed in this work. For the other weed species, the microorganisms had no control effects. In relation to the crops that showed the greatest sensitivity was the bean presenting leaf necrosis, followed by soybean and finally corn, in which the microorganisms did not present phytotoxicity.