Management Effects on Yield and Flavonoid Content in American Skullcap (Scutellaria lateriflora)

Abstract

American Skullcap (Scutellaria lateriflora) is a member of the mint family (Labiatae or Lamiaceae), and is a medicinal herb traditionally used for its mild relaxant properties attributed to its content of flavonoids. Field and greenhouse trials were conducted to determine management effects on dry matter yield and flavonoid content in American skullcap. The field experiment was conducted on Marvyn loamy sand (fine-loamy, kaolinitic, Thermic Typic Kanhapludults) with 0-2% slope in central Alabama, to determine the effect of timing and frequency of harvest on shoot yield and flavonoid content. The experimental design was 2X2 split plot factorial in a randomized complete block design with four replications of each treatment. The main factors were number of harvests in the first season (2008) - one harvest per season and two harvests per season. The sub factors were timing of harvests in the second season (2009) - early harvest and late harvest. In the first year (2008), harvesting twice gave 36 % higher yield than harvesting once. Baicalein had higher concentration and yield than other flavonoids in 2008. In the second year, there was no difference in yield between early or late harvesting but all the parameters considered in the study were significantly higher in first harvest than in the second harvest. Baicalin was higher in concentration and yield than other flavonoids in 2009.Flavonoid yield was 58% higher in the first harvest than in the second harvest in year 2 (2009). No residual effect from first year treatment was observed on yield in second year. Greenhouse trials were conducted (September 2010 and January 2011) to determine the effects of nitrogen (N), phosphorus (P) and potassium (K) fertilizer on biomass yield and flavonoid content of American skullcap. Plants were grown in fritted clay in plastic pots in the greenhouse. Separate experiments were carried out for N, P and K. Each experiment was carried out two times and consisted of six levels of each nutrient. The levels of treatment for N experiment were: 0 kg N ha-1, 50 kg ha-1, 100 kg ha-1, 200 kg ha-1, 400 kg ha-1 and 800 kg ha-1, for P experiment were: 0 kg ha-1, 20 kg ha-1, 40 kg ha-1, 80 kg ha-1, 160 kg ha-1 and 320 kg ha-1 and for K experiment were: 0 kg ha-1, 50 kg ha-1, 100 kg ha-1, 200 kg ha-1, 300 kg ha-1 and 400 kg ha-1. Each treatment received a standard rate of micronutrient solution as needed as well as the highest level of the other two major elements. The nutrients were supplied as solution. Regression analysis gave maxima for dry matter, baicalein and chrysin yield at 446 kg N ha-1, 412 kg N ha-1 and 351 kg N ha-1 for N fertilizer respectively in greenhouse 2. Dry matter yield exhibited a linear response to P application. The yield of scutellarein, baicalin, baicalein and chrysin increased with addition of P. Regression analysis gave maximum dry matter yield at 208 kg K ha-1 for potassium fertilizer. A linear response to K fertilization was observed for scutellarein concentration. American skullcap may be harvested twice in the first year and at least twice in second year or cultivation. N, P and K increased dry matter and analyzed flavonoids yield in the greenhouse experiment. Field experiments are required to validate the finding of the greenhouse experiment and to determine if three harvests may be carried out in second and subsequent years.