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Valtcho D. Zheljazkov, Charles L. Cantrell, Tess Astatkie and Ekaterina Jeliazkova

‘Native’ spearmint (Mentha spicata L.) is a widely grown essential oil crop worldwide and in the midwest in the United States. There is interest in expanding spearmint production to Wyoming and other states. However, there is no information to determine if spearmint would perform well under the Wyoming high-altitude and short-growing season and if its productivity and oil quality would be affected by fall frosts. The objective of this study was to evaluate the effect of fall frosts at the end of the cropping season on ‘Native’ spearmint productivity and oil profile. Spearmint plants were harvested at the following harvest dates (HDs): 14 Sept., 21 Sept., 28 Sept., 5 Oct., 12 Oct., 24 Oct., and 1 Nov. 2011. The HDs were selected to coincide with the fall frosts in northern Wyoming. Indeed, during that time, frost occurred on the following dates: 21 Sept., 10 Oct., 13 Oct., 15 Oct., 19 Oct., 20 Oct., 24 Oct., 25 Oct., 26 Oct., 27 Oct., 28 Oct., 29 Oct., 30 Oct., 31 Oct., and 1 Nov. 2011. The first heavy snow occurred on 3 Nov. Fresh herbage yields were higher at the 1 Nov. HD relative to the 14 Sept. HD, whereas the yields at the other HD were not significantly different. Generally, the oil content was high at 14 Sept., 21 Sept., and 5 Oct. HD and low at the 24 Oct. and 1 Nov. HD. Carvone concentration (42% to 75% range) in the oil reached a maximum at the 12 Oct. HD. The concentration of limonene was low at the first HD (14 Sept.) and higher at the other HDs. The yield of carvone (a function of the fresh herbage yields, oil content, and the concentration of carvone in the oil) was high at the 12 Oct. HD and low at the other HDs. In the spring of 2012, spearmint emerged in late April and was unaffected by the Wyoming winter or by the early spring frosts. This preliminary study suggests ‘Native’ spearmint may be a viable crop for northern Wyoming at elevation of ≈1170 m.

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Valtcho D. Zheljazkov, Charles L. Cantrell, Mateus Augusto Donega, Tess Astatkie and Bonnie Heidel

Podophyllotoxin is used for the production of the anticancer drugs etoposide, etopophos, and teniposide. Currently, podophyllotoxin is extracted from the Himalayan mayapple (Podophyllum hexandrum Royle). Some junipers and other species also contain the same natural product and have been explored as a domestic source for this compound. The objective of this study was to screen junipers in the Big Horn Mountains in Wyoming for podophyllotoxin. Twenty junipers (18 accessions of Juniperus horizontalis Moench. and two accessions of J. scopulorum Sarg.) were sampled in Mar. 2012 and analyzed for podophyllotoxin. Podophyllotoxin concentration in the samples varied from 0.058% to 0.673% with five accessions having podophylloxin concentration above 0.5%. This study demonstrated wide variation of podophyllotoxin in J. horizontalis and J. scopulorum in the Big Horn Mountains. Some of the accessions had greater than 0.5% podophyllotoxin making them a feasible source for podophyllotoxin extraction.

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Valtcho D. Zheljazkov, Charles L. Cantrell, William B. Evans, M. Wayne Ebelhar and Christine Coker

Sweet basil (Ocimum basilicum L.) and holy basil (Ocimum sanctum L.) are the most widely grown basil species in the world either for the fresh market or for essential oil production. Both species are considered to be promising essential oil crops in the southeastern United States; however, research on oil production and composition of these species in Mississippi and the southeastern United States is lacking. The objective of this study was to evaluate biomass productivity, oil content, and oil composition of sweet basil (Ocimum basilicum L.) cvs. German and Mesten and holy basil (Ocimum sanctum L.) cv. Local grown at four locations in Mississippi. Overall, the three basil cultivars grew well; the fresh herbage and essential oil yields at three of the locations were high and comparable to basil yields reported in the literature. Essential oil content in air-dry herbage and the essential oil yields were as follows: 0.07% to 0.50% and 0.7 to 11.0 kg·ha−1 in sweet basil cv. Mesten, 0.2% to 0.5% and 1.4 to 13.0 kg·ha−1 in sweet basil cv. German, and 0.08% to 0.40% and 0.6 to 5.3 kg·ha−1 in holy basil cv. Local, respectively. The main constituent of sweet basil cultivars was (–)-linalool with other constituents being (–)-camphor, α-humulene, eucalyptol, eugenol, (–)-bornyl acetate, methyl chavicol, (–)-trans-caryophyllene, α-trans-bergamotene, and cadinol. The main constituents of holy basil were methyl chavicol, eugenol, and eucalyptol with other constituents being α-humulene, humulene-epoxide II, (–)-trans-caryophyllene, α-trans-bergamotene, and γ-cadinene. Our results suggest sweet and holy basils have a potential as new essential oil crops for Mississippi and possibly the southeastern United States and can provide oil yields and composition typical for the respective species.

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

Peppermint (Mentha ×piperita) is currently not a common crop in the southeastern United States. Recently, there has been an interest in peppermint as an essential oil crop for this region. In 2007, a field experiment was conducted in Mississippi to determine the effect of nitrogen (N) (0 and 80 kg·ha−1), location (Verona and Stoneville), and harvesting stage (bud formation and flowering) on peppermint productivity, oil content, and composition. Peppermint biomass yields were higher at Verona (8.12 t·ha−1) than at Stoneville (6.12 t·ha−1). However, the essential oil content was higher at Stoneville (1.1%) than at Verona (0.6%). Generally, N rate at 80 kg·ha−1 did not affect oil yield and composition compared with 0 kg·ha−1. The concentrations of the major essential oil constituents were: (-)-menthol at 26% to 30%, (-)-menthone at 14% to 21%, (+)-menthofuran at 5% to 11%, and eucalyptol at 3% to 4% of total essential oil (wt/wt) and were generally within the values previously reported. The concentrations of (-)-menthone and (+)-menthofuran were significantly higher at Stoneville, 21% and 11%, respectively, than at Verona (14% and 6%). The (-)-menthol, (-)-menthone, and (+)-menthofuran yields/ha were higher at Stoneville than at Verona. Overall oil content and yields were higher at bud formation than at flowering, 1.3 and 1.8 times, respectively. In addition, the concentration of (-)-menthone and eucalyptol and the yields of (-)-menthone, (+)-menthofuran, and eucalyptol were higher at bud formation than at flowering. The results from this study demonstrated peppermint can be successfully grown in Mississippi and provide essential oil yields and composition comparable to those in the northwestern United States, the traditional peppermint-growing region.

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Valtcho D. Zheljazkov, Charles L. Cantrell, M. Wayne Ebelhar, Christine Coker and William B. Evans

Baikal skullcap (Scutellaria baicalensis) is an important medicinal plant with proven bioactivity. Commercially available products in the United States containing extracts or derivatives from this plant species have been shown to lack consistency of chemical composition and bioactivity. In the United States, these issues could be solved through domestic production of skullcap. The hypothesis of this study was that Baikal skullcap grown in the Mississippi climate would accumulate sufficient bioactive flavonoids, baicalin, and baicalein in the roots to justify domestic production, and that shoots of these plants might also contain the flavonoids of interest. A replicated field experiment was conducted at four locations in Mississippi (Beaumont, Crystal Springs, Stoneville, and Verona) to test the hypothesis. The concentration of the main flavonoid, baicalin, in the roots ranged from 8.1% to 15.6%, whereas the concentration of baicalein varied from 0.2% to 1.2%. The flavonoid concentrations in the roots were similar to that of commercially available skullcap roots, and to concentrations reported in the literature. Chrysin was detected in the roots from one location. Furthermore, the flavonoids apigenin, baicalein, baicalin, chrysin, and scutellarein were detected and quantified in the skullcap shoots. Overall, yields of dry roots tended to increase from southern to northern locations. This is the first report on flavonoid accumulation in Baikal skullcap roots and shoots grown in the United States. The results from this study are promising and suggest that 1) Baikal skullcap grown in Mississippi accumulates similar amounts of baicalein and baicalin to skullcap grown in other regions and can provide up to 128 kg·ha 1 of baicalin and up to 2.32 kg·ha 1 of baicalein; 2) flavonoid concentration in Baikal skullcap roots and shoots, yields, and mineral concentration of roots might depend on climatic and growing conditions; and 3) Baikal skullcap could be developed as a high-value crop for Mississippi and possibly other regions of the United States. Further research is needed on skullcap production methods and economic feasibility.

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Valtcho D. Zheljazkov, Charles L. Cantrell, M. Wayne Ebelhar, Dennis E. Rowe and Christine Coker

Nitrogen (N) and sulfur (S) were believed to be important nutrient management tools for the production of sweet basil (Ocimum basilicum L. ‘German’) with desirable oil content and composition and acceptable herbage yields. A multilocation research study was initiated to evaluate the effect of N (0, 60, 120, and 180 kg·ha−1 N) and S (0, 20, 40, and 80 kg·ha−1 S) rates on biomass production, oil content, and oil composition for sweet basil. The three locations in Mississippi (Stoneville, Poplarville, and Verona) were selected based on soil type, geographic, and climatic variation. Location, N rate, and their interaction were significant on basil dry herbage yields. The herbage yield means were 4967 kg·ha−1, 2907 kg·ha−1, and 2122 kg·ha−1 for Poplarville, Verona, and Stoneville, respectively. Oil content was significantly affected by location with means of 0.69%, 0.80%, and 0.64% for Stoneville, Poplarville, and Verona, respectively. Location, N, and S had significant effects on oil yields with means of 14.7, 38.7, and 18.5 kg·ha−1 for Stoneville, Poplarville, and Verona, respectively. The significant quadratic response of essential oil yields to N fertilization rates showed oil yields were maximized for fertilization between 50 and 60 kg·ha−1 N. In contrast, the response to S fertilization appeared to continue to increase beyond the maximum fertilization rate evaluated of 80 kg·ha−1 S. Location and N application rates had a significant effect on the yields of the major basil oil constituents (–)-linalool, eugenol, (–)-bornyl acetate, and eucalyptol, whereas S had a significant effect on eucalyptol yield only. Eucalyptol concentration was positively correlated to the concentration of (–)-bornyl acetate. This is the first study to quantify (in real concentration) the response of the major sweet basil oil constituents (–)-linalool, eugenol, (–)-bornyl acetate, and eucalyptol as a function of N and S application rates. Also, it is the first study to demonstrate a strong response of basil oil yield to S. The results from this study demonstrated that N and S applications can be used as management tools with respect to sweet basil production, oil content, and oil composition.

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Santosh Shiwakoti, Henry Y. Sintim, Shital Poudyal, Jennifer Bufalo, Charles L. Cantrell, Tess Astatkie, Ekaterina Jeliazkova, Lyn Ciampa and Valtcho D. Zheljazkov

Japanese cornmint, also known as menthol mint (Mentha canadensis L. syn M. arvensis L.), is an essential oil crop cultivated in several countries in Asia and South America. The plant is currently the only commercially viable source for natural menthol as a result of the high concentration of menthol in the oil compared with other crops. The hypothesis of this study was that harvesting at regular intervals within a 24-hour period would have an effect on essential oil concentration and composition of Japanese cornmint grown at high altitude in northern Wyoming. Flowering plants were harvested every 2 hours on 7 to 8 Aug. and on 14 to 15 Aug. and the essential oil was extracted by steam distillation and analyzed by gas chromatography–mass spectroscopy (GC-MS). The effects of harvest date (Harvest 1 and Harvest 2) and harvest time (12 times within a 24-hour period) were significant on oil concentration and yield of menthol, but only harvest date was significant on the concentration of menthol in the oil. The interaction effect of harvest date and harvest time was significant on water content and on the concentrations of menthol and menthofuran in the oil and on the yield of limonene, menthol, and menthofuran. Overall, the oil concentration in grams per 100 g dried material for the two harvests (1.26 and 1.45, respectively), the concentration of menthol in the oil (67.2% and 72.9%, respectively), and menthol yield (1066 to 849 mg/100 g dried biomass) were higher in plants at Harvest 2 as compared with plants at Harvest 1. The oil concentration was higher in plants harvested at 1100 hr or at 1300 hr and lowest in the plants harvested at 1500 hr. Menthol yield was the highest in plants harvested at 1300 hr and lowest in the plants harvested at 0700 hr, 1900 hr, or at 0300 hr. This study demonstrated that harvesting time within a 24-hour period and harvest date (maturity of the crop) may affect essential oil concentration and composition of Japanese cornmint grown at high altitude in northern Wyoming.