Ação de óleos essenciais no controle de Sclerotium rolfsii Sacc. em feijão-caupi

Abstract

Caused by the fungus Sclerotium rolfsii, the sclerotium wilt in cowpea has in chemical control an inefficient option, being the use of Essential Oils (OEs) an alternative to the control of the disease. The objective of this study was to evaluate the OEs of native plants of the Middle North Region (Lippia sidoides, Lippia lasiocalycina, Lippia origanoides, Lippia origanoides - Jatobá, Mesosphaerum suaveolens, Croton sonderianus and Croton zehntneri) in reducing S. rolfsii in in vitro and in vivo, and chemically characterize the evaluated OEs. The chemical composition of the OEs identified 73 compounds. Considering each species, the major constituents were thymol (L. sidoides); piperitenone oxide (L. lasiocalicyna); borneol (L. origanoides); carvacrol (L. origanoides - Jatobá); sabinene (H. suaveolens); β-sabinene (C. sonderianus); and estragol (C. zehntneri). The mycelial sensitivity of S. rolfsii in the presence of OEs in vitro at concentrations of 0.0313; 0.0625; 0.125; 0.2500 e; 0.500 ml kg -1 in Petri dishes with PDA medium. The S. rolfsii fungus was highly sensitive to the OEs of L. sidoides, L. origanoides - Jatobá and C. zehntneri. Identifying the most promising OEs, these were evaluated from seed treatment and biofumigation. In the treatment of seeds, seeds of the cultivar BRS Tumucumaque were used in concentrations 0.5; 1.0; 2.0; 4.0 e; 8.0 ml kg-1 of seed, conducted in Petri dishes with PDA medium and in pots, with infested soil. The effect of the treatment on the germination of the seeds was obtained with the standard germination test with paper roll. All oils reduced the mycelial growth of S. rolfsii in vitro. In vivo treatment, the use of seed treatment with OEs is effective at the concentration of 4.0 ml kg-1. Larger concentrations, despite having excellent levels of control, negatively interfere with seed germination. To evaluate the effect of biofumigation, oils were used at concentrations 3.18; 6.46; 12.8; 25.62 and; 51.25 μL plate-1 at different times (0; 24; 48 and; 72 h) of biofumigation. Concentrations of 3.18 μL plaque-1 completely inhibited sclerotia germination in vitro assays. In pots, with previously infested soil, the concentrations used were: 24.4; 48.8; 97.5; 195 e; 390 μl pot-1 at times of 0; 24; 48 e; 72 hours of biofumigation. The viability of S. rolfsii sclerotia was completely annulled when submitted to biofumigation with all OEs evaluated at concentrations equal to and greater than 3.18 μl plate-1. Sclerotium wilt is controlled by soil biofumigation with all OEs tested, being the best control obtained with L. sidoides.