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Valtcho D. Zheljazkov, Vasile Cerven, Charles L. Cantrell, Wayne M. Ebelhar, and Thomas Horgan

Peppermint is an aromatic plant grown for essential oil production, which is a major aromatic agent. Peppermint is also grown for production of dry leaves, which are used in herbal teas. The essential oil is used in a number of consumer products

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Weiguang Yi and Hazel Y. Wetzstein

members of the family have high phenolic and antioxidant content such as basil ( Ocimum basilicum ), lemon balm ( Melissa officinalis ), sweet marjoram ( Origanum majorana ), oregano ( Origanum vulgare ), peppermint, rosemary, sage ( Salvia officinalis

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Kelly J. Vining, Q Zhang, C.A. Smith, and T.M. Davis

Verticillium dahliae Kleb., is the most damaging disease of commercial peppermint ( Green, 1951 ; Lacy and Horner, 1965 ). With the goal of isolating genetic determinants of verticillium wilt resistance, we have identified highly resistant and susceptible M

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A.R. Mitchell, E.A. Rechel, and R.L. Dovel

Because peppermint (Mentha piperita L.) grows anew from rhizomes each spring, methods to measure the energy stored in the peppermint rhizomes would be useful. Our objective was to compare three methods of measuring carbohydrate in peppermint samples taken throughout a growing season. Total nonstructural carbohydrate (TNC) is a measure of the water- and acid-soluble sugars. Etiolated growth measurements of nonstructural biomass (NSB) are a reliable method for alfalfa (Medicago sativa L.) taproots. Near infrared spectroscopy (NIRS) is another method that has been used to determine TNC of alfalfa. Rhizomes were sampled monthly from four locations within a field. The NSB was correlated (r = 0.74) with the TNC means from each sampling date. The NIRS calibration was highly correlated with the TNC of all samples (R 2=0.96). Both NSB and TNC decreased in summer and increased in the fall as the plant stored carbohydrate for winter survival and regrowth. Any of the three methods could be used to study energy storage, although NIRS is the quickest, and NSB the least technologically sophisticated. Based on the positive results of NIRS, a more comprehensive calibration is warranted.

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Brent M. Chapman, James E. Barrett, and Terril A. Nell

Catharanthus roseus `Cooler Peppermint' were grown under four different watering regimes [well-watered (WW), wilt plus 1 day (W+1), wilt plus 3 days (W+3), and wilt plus 1 day during the last 2 weeks only (L W+1)] and two different light levels [1100 and 750 μmol·m–2·s–1]. Stress treatments affected finished plant size and leaf area as well as stomatal conductance, water potential and time to wilt during two dry-down periods imposed at the end of an 8-week production cycle. W+3 plants were 50% smaller with 50% less leaf area compared to WW plants. During the second dry-down period, WW plants in high light wilted in 2 days vs 4 days for the W+3 plants. Similarly, WW plants in low light wilted in 3 days vs 6 days for the W+3 plants. The W+3 plants maintained significantly higher water potentials and greater stomatal conductances than the other treatments throughout both dry-down periods.

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T.E. Bilderback, D.J. Cagle, and P.R. Fantz

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A.L. Fenwick and S.M. Ward

Seventeen mint accessions representing the three species grown for commercial oil production in the United States were characterized using randomly amplified polymorphic DNA (RAPD) analysis. The RAPD profiles readily identified the different Mentha species; calculation of genetic distance, based on the number of shared bands, indicated that M. spicata L. is more closely related to M. × gracilis than to M. × piperita. The RAPD profiles also distinguished among eight peppermint accessions of different geographical origin. However, only limited polymorphism was observed among the most widely grown peppermint and Scotch spearmint cultivars. These results indicate a potential lack of genetic diversity in mint cultivars grown for oil in the United States.

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Nan Wang and Barbara M. Reed

Roots of greenhouse-grown mint plants and in-vitro-grown shoot cultures were inoculated with Verticillium dahliae Kleb. conidial suspensions to study wilt symptom development and detection and elimination of the fungus. There were significant differences in the symptom expression between control and infected shoot cultures at all conidia concentrations for the four mints tested. Disease-symptom ratings were proportional to the V. dahliae inoculum density. Infected shoot cultures were stunted when inoculated with ≥ 103 conidia/mL. Verticillium dahliae was re-isolated from infected shoot cultures at all levels of inoculum, but not from any control cultures. Verticillium infections were easily detected by plating mint stems on potato dextrose agar. Shoot tips (0.5 to 15 mm) from infected in-vitro- and greenhouse-grown plants were isolated and screened for fungus. The most effective shoot length for fungus elimination was 3-5 mm. Shoot tips isolated from in vitro spearmint cultivars infected at 102 and 103 conidia/mL were 100% Verticillium free, but only 42% of `Black Mitcham' and 54% of `Todd's Mitcham' peppermints were free of the disease. Shoot tips from infected greenhouse plants produced Verticillium-free cultures from 79% of `Black Mitcham' and 90% of `Todd's Mitcham' plants. These results indicate the utility of testing for Verticillium and the safety of micropropagated mint shoots for certified planting stock programs.

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B.H. Alkire and J.E. Simon

An experimental steam distillation unit has been designed, built, and tested for the extraction of essential oils from peppermint and spearmint. The unit, using a 130-gal (510-liter) distillation tank, is intermediate in size between laboratory-scale extractors and commercial-sized distilleries, yet provides oil in sufficient quantity for industrial evaluation. The entire apparatus-a diesel-fuel-fired boiler, extraction vessel, condenser, and oil collector-is trailer-mounted, making it transportable to commercial farms or research stations. Percentage yields of oil per dry weight from the unit were slightly less than from laboratory hydrodistillations, but oil quality and terpene composition were similar.

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Stanley Ries, Rebecca Baughan, Muraleedharan G. Nair, and Robert Schutzki

Several plant species that are not consumed by animals were collected, extracted with organic solvents, and tested at different venues for their effectiveness as animal feeding repellents. Species with the most repellent activity were daffodil (Narcissus pseudo narcissus), bearded iris (Iris sp.), hot pepper (Capsicum frutescens), catnip (Nepeta cataria) and peppermint (Mentha piperita). Considerable effort was expended to isolate and identify compounds from these species responsible for repellent activity. Eight chemicals have been isolated and purified, and four of them have been identified. Both daffodil and catnip contain more than one repellent, but none of the four compounds identified were common to both species. Combinations of extracts from more than one plant species proved to have more repellent activity than extracts from individual species used alone. In several tests these plant extracts proved to be as effective or better than available commercial repellents. A plethora of additives and surfactants were tested to increase repellent activity by enhancing the spreading, penetration or persistence of the extracts.