Abstract

Amongst the most important agricultural products in Brazil, the soybean stands out, mainly as an export good. One of the end-of-cycle diseases, Anthracnose, caused by the fungus Colletotrichum truncatum (Schwein.) leads to severe damage to grain quality and yield. The use of natural products as a substitute for conventional pesticides for plant diseases control is an alternative found to reduce food contamination and environmental impacts. However, despite the progress made, much work still needs to be done to enable the safe and effective use of alternative products. Thus, this study aimed to test efficacy of noni essential oil (EO), combined with adjuvants, in the control of anthracnose in soybean plants. Gas chromatography was performed to identify the chemical profile of the EO. In vitro mycelial growth inhibition tests and analyzes on the stimulation of phytoalexin production were also performed. In the field trial, two soybean cultivars submitted to EO were used combined with orange and mineral oils as adjuvants. Octanoic acid (OA) was identified as the major component of EO. There was efficacy in the control of C. truncatum by EO and OA in vitro, as well as the induction of the production of the phytoalexin gliceolin in soybean seedlings with an increase of almost 80% with OA but with no impact on the growth of Trichoderma sp. Between the soybean cultivars tested, Coodetec 2728 IPRO presented lower severity to anthracnose symptoms, however, the cultivar Brasmax Foco demonstrated good tolerance to pathogen’s attack maintaining high productivity. Application of fungicides on the cultivar Coodetec 2728 IPRO resulted in a detrimental effect on yield possibly due to induction of the green stem syndrome formation in plants and a harvest delay of 15 days.

Key words: Morinda citrifolia L., Glycine max L.; Colletotrichum truncatum, Trichoderma sp, alternative control.