Fungitoxic activity of 12 essential oils against four postharvest citrus pathogens: Chemical analysis of Thymus capitatus oil and its effect in subatmospheric pressure conditions

The fungitoxic activity against Penicillium digitatum, Penicillium italicum . Botrytis cinerea, and Alternaria citri of 12 essential oils (EOs) distill ed from medicinal plants is reported. The results of the in vitro trials sh ow strong fungitoxic activity of Thymus capitalus (L.) Hofmgg EOs, which in hibited the growth of the four fungi at a concentration of 250 ppm (vol/vol ). The other 11 essences reduced the development of the fungi from 95 to 9% at 250 ppm (vol/vol). The fungitoxic activity of T. capitatus EOs (75, 150 , and 250 ppm) on healthy orange fruits, inoculated with P. digitatum (10(8 ) conidia ml(-1)) by spraying and placed in 10-liter desiccators, was weak at atmospheric pressure (3 to 10% inhibition at all three concentrations), while in vacuum conditions (0.5 bar), conidial mortality on the exocarp was high (90 to 97% at all three concentrations). These data proved not to be statistically different from treatments with thiabendazole-TBZ (2,000 ppm). Scanning electron microscope observations showed that T. capitatus EO vapo rs altered the morphology of P. digitatum hyphae and conidia. The gas-chrom atographic analyses of thyme EO indicated that carvacrol was present at 81 to 83%, p-cymene at 4.5 to 5%, gamma -terpinene at 2.6 to 3.3%, caryophylle ne at 1.5 to 1.6%, beta -myrcene at 1.6%, and linalool at 1.1 to 1.2%. Carv acrol proved to be the most important fungitoxic compound among the thyme E O constituents, but, unlike thyme EO, it caused alterations to the fruit at the concentration of 75 ppm.