|GIESBRECHT, FRANCIS - NC STATE UNIVERSITY
Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2004
Publication Date: 9/1/2004
Citation: Whitaker, T.B., Dorner, J.W., Giesbrecht, F.G., Slate, A.B. 2004. Variability among aflatoxin test results on runner peanuts harvested from five-foot field plots. Peanut Science. 31:59-63.
Interpretive Summary: Aflatoxin is a cancer-causing compound produced by fungi found in production fields. The U.S. Food and Drug Administration and the U.S. Department of Agriculture have aflatoxin inspection programs to identify and remove contaminated peanut shipments from the market chain. Scientists are attempting to breed peanuts that are resistant to fungal infection, which should reduce aflatoxin contamination in peanut shipments. To determine if peanut breeding lines are resistant to fungal infection, aflatoxin is measured in peanut samples taken from fields where various breeding lines are grown. It is difficult to know the true effect of a breeding line on aflatoxin reduction because of the large variability of aflatoxin values among the samples taken from a production field. To help the breeder get a better understanding of whether specific breeding lines effectively reduce aflatoxin, a study was developed to (1) measure the variability of aflatoxin among peanut samples taken from a production field and (2) determine the effect of increasing sample size on reducing variability. Equations were developed for the breeder to compute the size sample needed to reduce variability. Knowing the effect of sample size on variability, breeders can design experiments to get a more accurate estimate of the effect of a breeding line on reducing aflatoxin in peanuts.
Technical Abstract: An experiment was conducted to determine the variability associated with aflatoxin contamination among peanuts taken from plants grown in specified row lengths. Runner peanuts (cv. Georgia Green) were planted in ten 250-foot rows (6 seed/foot) and grown using standard production practices. Plants were exposed to natural late-season drought conditions making the peanuts susceptible to preharvest aflatoxin contamination. Plants were mechanically dug, inverted, and separated into 500 five-foot sections (plots). Peanuts from each numerically identified plot were harvested with a mechanical picker, dried to 8% kernel moisture (w.b.), shelled, and analyzed for aflatoxin by HPLC. The average kernel mass and weighted average aflatoxin concentration for all 500 plots was 131.4 g and 2,277.6 ng/g, respectively. The kernel mass varied among the 500 plots from a low of 4 g to a maximum of 283 g. The aflatoxin concentration among the 500 plots varied from a low of 0 ng/g to a maximum of 32,142 ng/g. The standard deviation among the 500 plot aflatoxin values was 4,061. The standard deviation among sample concentrations for this field study is very similar to previous studies that measured the standard deviation among samples concentrations taken from bulk farmers' stock lots. Increasing plot length by combining plots, using weighted aflatoxin concentrations, decreased the standard deviation among plot aflatoxin values as predicted by statistical theory. For example, increasing plot row length by a factor of four, or from five to 20 feet, decreased the standard deviation by a factor of two, or from 4,061 to 2,031. A regression equation was developed to predict the effect of plot row length on the variability among aflatoxin plot values. This information is useful for designing field plot experiments to test various strategies for reducing or preventing preharvest aflatoxin contamination.