SAMPLING A POISONOUS PLANT-POPULATION - QUANTIFYING TOXIC ALKALOIDS IN TALL LARKSPUR (DELPHINIUM-BARBEYI) LEAVES

Poisonous plants and noxious weeds are often chemically examined to de termine concentrations of secondary metabolites which are responsible for their toxic or biological activity. This study examined sample siz e requirements and sample methods necessary to quantify accurately the concentrations of individual and total toxic alkaloids in two tall la rkspur populations. A high performance liquid chromatography analytica l method was utilized to determine toxic alkaloid concentrations in al l leaves from three individual plant stems and leaves from the remaini ng stems (remainder) from each of 50 plants in each population, To obt ain high precision in quantifying toxic alkaloids in the larkspur popu lations (within 2.5 to 5% of the population mean, 0.95 confidence), ve ry large numbers of samples (>50-200) were required. However, lower pr ecision (within 10% of the population mean, 0.90-0.95 confidence) requ ired only 20 samples. Similarly, testing parameters relating to toxin concentration in tall larkspur populations within 5 or 10% of the popu lation mean also required hundreds of samples at power levels of 0.95 and alpha-levels of 0.05. Relaxing power and a-level requirements to 0 .80 and 0.1 respectively, reduced sample size to about 30. The means o btained by four different sampling methods were similar (P > 0.05). Al kaloid concentrations in leaf samples from single stems were highly co rrelated to whole-plant leaf (remainder) samples (r(2) greater than or equal to 0.76), indicating that harvesting leaves from single stems p rovided representative samples of the entire plant. The results indica te the difficulty in obtaining accurate information about toxins in po isonous plant populations for risk assessment by livestock producers o r extension agents and demonstrate the necessity for efficient analyti cal methodology. Researchers evaluating concentrations of plant compou nds in other weeds or toxic plants should consider variability, sampli ng procedure, and sample size before experiments begin.