Disinfection of Seed Surfaces with Sodium Hypochlorite

Abstract

Surface disinfection for the purpose of determining the presence of internal fungi in grains or seeds gave variable and sometimes erroneous results. Aspergillus glaucus grew from as many as 100% of wheat kernels that were free of viable internal fungi but that had been heavily surface-inoculated before being treated with sodium hypochlorite (NaOCl) and plated on agar. Spores of Aspergillus spp. were killed almost instantaneously by 1-5% solution of NaOCl, so the problem appeared to be lack of contact between spores and NaOCl because of air bubbles, cracks, surface hairs, debris, etc., on seed surfaces. Rinsing seeds in wetting agents or detergents before treating with NaOCl did not improve effectiveness, but rinsing in ethanol before NaOCl was effective in reducing surface contamination, especially with wheat. One brand of NaOCl with lower pH and lower total alkalinity than others was the most effective surface disinfectant. Reducing the pH of NaOCl solutions from pH 11-12 to about pH 8 increased effectiveness, but such solutions were unstable. Destruction of spores on seed surfaces depends on the kind and condition of seeds; the amount of surface contamination; the brand, pH, and concentration of NaOCl; and exposure time. Some literature reports on growth of storage fungi in grain may be inaccurate because of failure to eliminate surface contaminants.