Potencial alelopático de resíduos de Bidens pilosa e Eragrostis plana na emergência e crescimento de Lactuca sativa

Abstract

In the allelopathy science the secondary metabolites produced by one plant can cause positive or negative effects in the development of another, these substances are called allelochemicals. The aim of this work was to evaluate possible allelopathic effects of Bidens pilosa and Eragrostis plana extracts on emergence and growth of Lactuca sativa. For the extracts young plants were collected in the vegetative phase and adults in the reproductive phase of Bidens pilosa and leaves in the vegetative phase of Eragrostis plana, which were dried in draying oven and crushed obtaining an extract of these plants. Two different experiments were carried out with Lactuca sativa: experiment 1 with the Letuce may queen (butter) variety from ISLA Seeds, using soil as substrate and experiment 2 with the TE70 (robust) variety from TECNOSSEED Seeds on commercial substratum Carolina Padrão. Experiment 1 was seeded in control treatment with soil only. The treatments with Bidens pilosa extract were considered a high population of plants at the reproductive stage and high population of young plants at the vegetative stage; treatments with Eragrostis plana, it was considered high and low population of plants in the reproductive stage. In experiment 2, the soil was replaced by commercial substratum following the same previous treatments, but also treatment with low population of Bidens pilosa at the reproductive stage, later the plants were transplanted to pots with soil. The extracts were proportional to the amount of dry matter found in one hectare infested with the plants under study. The variables evaluated were emergence of seedlings in days after sowing (DAS), length of the root system, emergence of seed bank plants; for experiment 2, the same variables of experiment 1 were evaluated, further leaf quantity and green and dry matter weights. In the experiment 1, the control treatment reached 100% emergence of plants, while the other treatments, besides prolonging for a greater number of days, varied in percentage, with the high population of Bidens pilosa 17% emergence. Treatment 2 was 100% emergency in all treatments. Seed bank emergence occurred in all treatments that used soil, with incremental increase as the possible allelopathic effects diminished. The root system of experiment 1 differed at 20 DAS. For experiment 2 did not differ at 20, but at 49 DAS there was difference between treatments. Regarding leaf production, green matter weight and dry matter of experiment 2, the control treatments and low population of Eragrostis plana presented higher mean values in relation to the other treatments. Based on the results obtained it is concluded that Bidens pilosa and Eragrostis plana can cause negative allelopathic effects at the early development of the lettuce culture.