Effect of Shade, Irrigation and Nutrients on Dry Matter Yield and Flavonoid Content of American Skullcap

Abstract

Growing interest in medicinal herbs results in a need to domesticate medicinal plants traditionally harvested in the wild. American skullcap (Scutellaria lateriflora), native to moist habitats in eastern North America, has sedative properties associated with the flavonoid, baicalin, and also contains baicalein, chrysin, wogonin and lateriflorin which have multiple uses. Information on how growing conditions affect dry matter yield, concentration and flavonoids yield is lacking. A field experiment was conducted at the EV Smith Research Center near Shorter Alabama in 2007 and 2008 to explore the effect of light, irrigation and nutrient application on dry matter yield and flavonoid concentration and yield of American skullcap. The field experiment was a 2 x 2 x 3 split vi plot factorial in a randomized complete block design with shade as the main factor and irrigation and nutrients as subplots. Treatments were: shade (40% vs. no shade), irrigation (applied at 30 kPa vs. no irrigation and nutrients (no nutrients vs. fertilizer: 100 kg N, 68 kg P and 42 kg K ha-1) vs. (chicken litter: 100 kg N, 50 kg P and 123 kg K ha-1). Four harvests were carried out in 2007 and 2008 to determine dry matter yield and flavonoid content. Extraction of plant material was performed using the Accelerated Solvent Extraction method and extracts were analyzed by the HPLC method to determine flavonoid concentration. All parameters considered in our study, except percent dry matter, performed better under shade than in full sun. Higher density was observed in 2008 due to spreading after removal of mulch fabric, however a decrease in stand was observed in the nonirrigated treatments in full sun. Powdery mildew was a problem encountered mainly under shade. Dry matter yield was 45% higher under shade, 61% higher with irrigation and 22% higher with added nutrients. Dry matter yield was not different according to nutrient source. A significant interaction of irrigation by nutrients was also observed. The highest dry matter yields were obtained with the irrigation + manure and irrigation + fertilizer treatments under shade and the lowest yield with fertilizer and the control treatments in full sun. Shade decreased baicalin concentration but did not affect baicalein, wogonin and chrysin concentration. Irrigation increased baicalin, baicalein and wogonin concentration but had no effect on chrysin concentration. Nutrient application slightly increase baicalin and chrysin but did not affect baicalein and wogonin concentration. Total flavonoid concentration was 26% higher in full sun, 20 % higher with irrigation and 29% lower vii with added nutrients. Significant interactions of shade by irrigation and shade by nutrient were observed for baicalin and baicalein concentrations. The highest concentrations were obtained with the irrigation + manure and irrigation in full sun and the lowest with manure under shade. Shade, irrigation and nutrients increased yield of all four flavonoids. Total flavonoid yield was 26% higher under shade, 97% higher with irrigation and 44% higher with added nutrients. Significant interactions of shade by irrigation, shade by nutrients and irrigation by nutrients were also observed for flavonoid yield. The highest flavonoid yields were observed with the irrigation + manure and irrigation + fertilizer treatments under shade and the lowest with the control and fertilizer treatment in full sun. Higher dry matter and flavonoid yields were obtained with the same treatments, suggesting that increasing dry matter yield had a direct effect on flavonoid yield. Based on our results, we can recommend irrigation and added nutrients for higher dry matter and flavonoid yield and irrigation with added nutrients in full sun for higher flavonoid concentration.