Submitted to: Acta Horticulturae
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/4/2003
Publication Date: 12/1/2003
Citation: PLOTTO, A., ROBERTS, R.G., ROBERTS, D.D. EVALUATION OF PLANT ESSENTIAL OILS AS NATURAL POSTHARVEST DISEASE CONTROL OF TOMATO (LYCOPERSICON ESCULENTUM). ACTA HORTICULTURAE. 2003. v. 628. p. 737-745. Interpretive Summary: The postharvest decay of fruits and vegetables requires the use of fungicides, but consumers are becoming concerned about chemical residues. In addition, chemical fungicides are becoming increasingly limited and regulated. Alternative non-chemical methods that include the use of natural essential oils were investigated in this study. These oils were tested for their anti-fungal activity in petri dishes and then on fungi-inoculated tomato fruit. Thyme and oregano oils controlled two postharvest decay organisms on tomato, although in some cases, there was damage to the tomato fruit at the high levels of oil needed to inhibit decay.
Technical Abstract: Essential oils with fungicidal activities were identified in vitro; these were oregano, thyme, lemongrass, and cilantro. Essential oil components in those plants with antimicrobial activity were carvacrol, thymol, citral, and trans-2-decenal, respectively. Vapors of thyme, oregano and lemongrass, and their respective major component showed complete growth inhibition of Botrytis cinerea and Alternaria arborescens. Geotrichum candidum was more sensitive to citral and citral-containing oil vapors than to thyme or oregano oils. Only vapors of thyme oil, oregano oil, thymol and carvacrol inhibited Rhizopus stolonifer. When incorporated into the activity on all four fungi at 500 mg/L. Lemongrass oil had only an effect at 1,000 mg/L, and no inhibition of Rhizopus. Trans-2-decenal was fungicidal to Botrytis, Alternaria and Geotrichum as vapor, but lost its activity when incorporated into the growth medium. Essential oil vapors were not successful in stopping disease development in inoculated tomatoes. Additionally, some oil vapors appeared to induce phytotoxicity on treated fruit under long periods of exposure. Emulsions of oils of thyme and oregano at 5,000 ppm and 10,000 ppm as dip treatments reduced disease development in tomatoes inoculated with B. cinerea and A. arborescens.