Role of Essential Oils in Control of Rhizoctonia Damping-Off in Tomato with Bioactive Monarda Herbage

Abstract

Plants in the genus Monarda produce complex essential oils that contain antifungal compounds. The objectives of this research were to identify selections of monarda that reduce Rhizoctonia damping-off of tomato, and to determine relationships between essential oil composition of 13 monarda herbages (dried and ground leaves) and disease suppression. Herbages were grouped into five chemotypes, based on essential oil composition and effective concentrations for reducing growth by 50% for Rhizoctonia solani. Replicated and repeated disease control assays were conducted with monarda herbages in greenhouse medium, with or without Rhizoctonia. Percent survival, seedling height, and stem diameter were evaluated at 8 weeks. Survival, seedling height, and stem diameter in herbage-only treatments were not different from the control (no-herbage, no-pathogen) for most herbage treatments. In the pathogen control (no-herbage + Rhizoctonia), seedling survival was 10% that of the control. In pathogen-infested media, seedling survival ranged from 65 to 80% for treatments with thymol chemotypes and 55 to 65% for carvacrol chemotypes. Effective control of Rhizoctonia damping-off was correlated with phenolic monoterpenes; herbages classified as carvacrol chemotypes effectively protected tomato seedlings from Rhizoctonia damping-off disease without phytotoxicity. This study provides evidence that monarda herbages have potential as growing media amendments for control of Rhizoctonia damping-off disease.

Natural Fungicides Obtained from Plants

“…and peppermint (Mentha x piperita L.), also reduced growth of R. solani. Growth of R. solani was completely suppressed by the phenolic monoterpene, carvacrol at a concentration of 100 mg mL -1 and by its structural isomer, thymol, at a slightly higher concentration (150 mg mL -1 ) (Gwinn et al, 2010). Carvacrol was the major constituent of essential oils collected from Thymbra spicata L., a member of the mint family that grows wild in the eastern Mediterranean; oil extracted from T. spicata completely suppressed growth of R. solani.…”

“…Growth of R. solani was reduced when grown on culture medium amended with oils of Monarda didyma or when exposed to the vapours in a microatmosphere test (Gwinn et al, 2010). When dispersed in fungal culture media, oils from thyme (Thymus vulgaris L.), Salvia fruticosa Mill.…”

“…Carvacrol was the major constituent of essential oils collected from Thymbra spicata L., a member of the mint family that grows wild in the eastern Mediterranean; oil extracted from T. spicata completely suppressed growth of R. solani. Fungicidal activity of thyme oils has been correlated with thymol content (Gwinn et al, 2010).…”

“…Losses due to Pythium myriotylum were reduced when monarda herbage (ground, dried leaves) from some varieties of Monarda didyma L., M. clinopodia L. and M. menthifolia L. were added to greenhouse growing medium at a rate of 10% (v/v) (Gwinn et al, 2010). Thymol was the major essential oil component of 'Croftway Pink', the most effective monarda herbage treatment for reducing losses due to P. myriotylum.…”

Antifungal Studies of Selected Essential Oils and a Commercial Formulation against Botrytis Cinerea

“…Similarly, plants in the genus Monarda produce complex essential oils that contain antifungal compounds and are reported to inhibit the growth of Rhizoctoniasolani K. (Fraternale at al., 2006;Gwinn et al, 2010) and Sclerotiniasclerotionum (Gwinn, Greene, Trently, & Ownley, 2006). However to date, no study has been done to investigate the effect of essential oils of Monardaon B. cinerea.…”