Peróxido de hidrogênio (H2O2) para controle de Pythium myriotillum em alface (Lactuca sativa L.) cultivada em sistema hidropônico

Abstract

The cultivation of lettuce in a hydroponic system, which began in the 90s in Brazil, has been expanding ever since, due to the advantages it presents to the farmer and the quality of the product offered to the end consumer. This system is greatly affected by the occurrence of Pythium spp., which causes root rot in lettuce, especially in hot and humid climate conditions. In this context, the objective was to evaluate the use of hydrogen peroxide (H2O2) to controlPythium myriotillum in lettuce grown in a hydroponic system under climatic conditions in the Central Amazon. To this end, the vegetative growth of lettuce plants was evaluated by applying increasing doses of H2O2 in the nutrient solution inoculated and not inoculated with P. myriotylum. Experiments (1 and 2) were carried out between the months of June and October 2024, corresponding to the Amazonian summer period. A randomized block design (DBC) was used, consisting of four blocks and six treatments. In experiment 01, H2O2was applied every two days, using dosages (mL 1000 L-1) of 0.3; 0.6; 0.9. In experiment 02, doses (mL 1000 L-1) of 6, 24, 42 were evaluated, applied daily. At the end of the cultivation cycle, the plants were harvested, and the response variables were measured: fresh and dry mass of the roots and aerial parts, stem length and number of leaves and number of dead plants. Data were subjected to the Shapiro–Wilk test, ANOVA and Scott-Knott test of means. From an extensive literature review, it was found that this is the first report of P. myriotylum in Amazonas. The symptoms that this species triggered were necrosis at the ends of the roots, progressing to the entire root system, and intensification of wilting of the aerial part during the hottest hours of the day. In experiment 1, cross-contamination occurred between treatments, probably due to contaminated equipment, while in experiment 2, with revised methodology, the pathogen was re-isolated only from the inoculated plants. The abrupt changes in pH, dosage and frequency of H2O2 applications apparently interfered with its performance in controlling the symptoms of the disease. Thus, there was no total reversal of symptoms, but the dosage of 42 mL 1000 L-1 promoted an increase in height, root and aerial part dry mass of lettuce plants, equaling them to non-inoculated treatments. The use of H2O2 also reduced plant mortality. 6 doses; 24 and 42 mL 1000 L-1 showed an average of 20% mortality compared to 60% in the inoculated control that did not receive application of H2O2."