FIELD PRODUCTION OF TEXAS NATIVE EVENING PRIMROSE (OENOTHERA SPP.) AS A SOURCE OF GAMMA LINOLENIC ACID

Abstract

Gamma linolenic acid (GLA) has been recognized as a beneficial treatment for a variety of human ailments including high blood pressure, cardiovascular disease, skin disorders, and diabetic neuropathy. Oenothera biennis has been the most widely used species of evening primrose to produce GLA. Over a period of two years, native accessions of O. elata, O. jamesii and O. rhombipetala were produced as transplants in a greenhouse and mechanically transplanted to the field using three different plant spacings. Plots were harvested and analyzed to determine seed yield, oil content and GLA level. In the two years of this study, seed yield, oil content and GLA level were significantly impacted by plant spacing treatments. Generally, the higher plant populations gave the best results. INTRODUCTION Historically, evening primrose (Oenothera spp.) has been grown both as an attractive wildflower and as an herbal supplement. Increasingly, evening primrose oil has been recognized by the medical community as a legitimate health care product. Researchers have found that the high levels of gamma linolenic acid (GLA) (C18:3 ∆6, 9, 12) found in evening primrose oil can be used to treat many of the pathological conditions in humans caused by GLA deficiencies. Recent research has indicated that GLA may reduce the symptoms of diabetes mellitus and atherosclerosis (Hathaway, 1999; Keen et al., 1993). Supplementation of the diet with the GLA derived from the oil of plants such as evening primrose is thought to reduce the severity of many diseases (Mengeaud, Nano, Fournel and Rampal, 1992). Commercially, Oenothera biennis is used for GLA production; however, the best production with this crop occurs in cool moist climates. Previous research has identified the Texas natives Oenothera jamesii, Oenothera elata and Oenothera rhombipetala for their high levels of GLA and their ability to thrive in demanding climates while producing economic quantities of GLA (Balch, McKenney and Auld, 1998 and 2002). Published information on the current production of evening primrose oil involves transplanting young plants of Oenothera biennis from the greenhouse to the field in what can be an expensive and labor intensive task (Brandle, et al., 1993; Nightingale and Baker, 1995). Very little published information as to the specifics of this process are available. Plug transplanting by mechanical means is a common method for many flower and vegetable crops and appears to be a viable solution. The purposes of this study were to determine the optimal cultural management for field production of evening primrose in a semiarid climate and to attempt to reduce the seed dormancy present in these species. MATERIALS AND METHODS Accessions of O. rhombipetala (R-36 and R-46), O. elata (R-50) and O. jamesii (T-60) were seeded in the greenhouse using a peat-lite media. Water and fertility were maintained consistently throughout the process as necessary. At 11 weeks after seeding, the transplants were mechanically transplanted in the field using a Rotary One (Holland Transplanters, Holland, MI) in one meter spaced rows. Plant spacing was 30, 60, or 90 cm. Irrigation was supplied as necessary throughout the growing season. Flea beetles were a significant problem and were managed using applications of a carbaryl insecticide at the recommended rate. At maturity, adjacent plants within a 3.5 m sampling unit of the Proc. XXVI IHC – Future for Medicinal and Aromatic Plants Eds. L.E. Craker et al. Acta Hort. 629, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 284 9.14 m blocks were harvested by hand, threshed and the seed screened with 12.7 cm perforated plate soil sieves (Humboldt Mfg., Norridge, Il). Seed samples were then cleaned and final seed weight determined. The experiment was evaluated as a randomized complete block design with four replications. Each of the four accessions was evaluated in separate experiments. Data were analyzed by analysis of variance (SAS, Version 7 1998) and means separated with a Fisher’s Protected Least Significant Difference Test at the 0.05 probability level. Oil content was determined by nuclear magnetic resonance (NMR) using a canola seed sample as a standard. RESULTS AND DISCUSSION A uniform stand of the three species was successfully established using the mechanical transplanter and appears to be a viable alternative for commercial production. Development in the field for each of the four accessions (R-50, T-60, R-36, R-46) varied due to species differences, but were consistent in maturity from weeks after seeding (WAS) between the two years. R-36 and R-46 varied the least developmentally being the same species. The three different plant spacings of evening primrose were evaluated for seed yield. The seed of each accession was hand harvested when the seedpods began to shatter. Even though individual plant yields varied and often improved with increased distance between the plants, the improvement was not enough to offset the greater numbers of seed obtained with decreased spacing and increased plant populations per hectare. All spacings were sufficient to allow for normal growth. Yield data for all of the species is presented in Fig. 1. The two O. rhombipetala accessions R-36 and R-46 were harvested at 28 WAS (the beginning of September) and exhibited flower abortion along the stem, possibly due to a response to heat. The smaller number of ripened capsules resulted in a consistently smaller yield throughout the O. rhombipetala samples. O. jamesii (T-60) was harvested at 35 WAS when the pods began to shatter. This entire plant was much larger and woodier than any of the other evening primrose in the study. All of the evening primrose are indeterminate; however, the O. jamesii had much more leafy growth at the time of harvest making the determination of time of harvest more difficult. The more moderate seed yield may be due to the pods shattering and loosing seed while this indeterminate plant kept flowering. O. elata (R-50) took place 37 WAS (the last week of November). In 1999, O. elata had the highest yields; however; during 2000 excessively cold weather began early and caused a loss in seed yield for R-50. The slightly smaller capsules did not split early and were more easily threshed. Approximate weights per 100 seeds for each of the accessions were determined. O. elata (R-50) weighed 0.03 g, O. jamesii (T-60) weighed 0.06 g and O. rhombipetala (R-36) and (R-46) weighed 0.02 g each. The plant populations of 10.8 thousand plants ha (90 cm. spacing) gave significantly poorer seed yields with O. elata than 16.1 (60 cm.) and 32.3 thousand (30 cm.) plants ha for both years. O. jamesii (T-60) showed higher seed yields with 32.3 thousand plants ha than 16.1 thousand plants ha and 10.8 thousand plants ha. Seed yields for both species greatly decreased in the 2000 season. O. rhombipetala (R-46) showed no significant differences between any of the spacing treatments while O. rhombipetala (R-36) showed significant improvement when planted with the narrowest spacing but showed very little difference between the other two and over the two years (Fig. 1). The percent oil content was determined from the four highest seed yielding individual samples of each 3.5 m replication in both years. The results of the percent oil are presented in Fig. 2. Oil yield for O. elata was much higher in 1999 than 2000 while spacing appeared to have no significant affect on a percent basis (Fig. 2). Because O. rhombipetala matures much earlier in the season, the percent oil did not appear affected over both years. NMR determined the percent GLA from the four highest seed yielding individual samples in a 3.5 m harvest area. The results of this analysis are presented in Fig. 3. O.