Antifungal Activity of Spearmint and Peppermint Essential Oils against Macrophomina Root Rot of Cotton

Abstract

Essential oils as natural antifungal substances one of the alternative methods for plant disease control. The present study was conducted during 2015 and 2016 to investigate the antifungal activity and oil constituents of volatile oils from spearmint (Mentha viridis L.)and peppermint( Mentha piperita L.) against cotton root rot pathogen (Macrophomina phaseolina). Gas chromatographic analysis revealed that spearmint volatile oilwas constituted by carvone (60.16%) as a major component followed by 1,8 cineole (8.67%), limonene (7.40 %), dihydro carvone (5.86 %), β- ocimene (4.29%) and pulegone (3.23%). While peppermint volatile oilwas rich in menthone (46.52%), menthol (25.88%), limonene (7.72%) menthyl acetate (3.90%), iso menthol (2.10%) and sabinene (2.03%). Both essential oils with different concentrations were evaluated in vitro against three fungus isolates. The two tested oils exhibited 89.55 inhibition percent for the crude oils, against all the tested fungal isolates. Moreover, it was noticed that as oil concentrations decreased, the inhibitory effect also decreased. At the same time, a highly significant effect of oils at all concentrations was observed during sclerotial formation (number and size). The use of essential oils as seed treatment exhibited a highly significant reduction in disease incidence of cotton which has been artificially infested with root rot patho­gen, compared to fungicide and untreated control treat­ments under the greenhouse conditions. This reduction was calculated to be between 4.56 and 100% compared with a 26.67% reduction with the utilization of Topsin M treatment at the pre-emergence stage. At the post-emergence stage, all applied treat­ments were able to decrease the percentage of root-rot incidence. Reduction ranged between 66.67 and 100% over the untreated control. Reduction in disease incidence was reflected in a survival plants increase of 34.62–96.17% and 73.09–126.9% for spearmint and peppermint volatile oils, receptively. Results in the current study demonstrated, that application of peppermint essential oils has an observer influence on the plant growth (plant height), which differ significantly from this of spearmint oil.