Home Onion Seed Disinfestation Methods

We performed initial screening of a range of methods that have been suggested in the popular media for home seed disinfestation. The goal was to identify candidate disinfestation methods that significantly reduced fungal contamination of seeds prior to sprouting and that did not adversely affect germination rates. We performed these initial tests on onion seeds because our initial assessments suggested they had consistently high surface contamination with both fungi and bacteria. Seeds were aseptically removed from the source bag, and 0.25 g (58 ± 6 seeds) were placed into sterile 2-mL Eppendorf^TM (Hamburg, Germany) microcentrifuge tubes for each of three replicates of 25 different disinfection treatments. Chemical treatments included (1) sterile deionized water (2 min), (2) sodium hypochlorite (0.6% NaOCl; 10% household Clorox bleach, 2 min), (3) hypochlorous acid (HClO; freshly prepared Force of Nature^TM Multi-purpose cleaner (Westford, MA, USA), ~800 ppm chlorine, 2 min), (4) hydrogen peroxide (3%, 2 min), (5) ethanol (70%, 2 min), and (6) glacial acetic acid (5%; similar to vinegar). Each of these six chemical treatments was performed both as a simple soak with agitation and with a 2-min suspension in a water-bath sonicator. Heat treatments were conducted as (1) boiling in sterile deionized water (1 min), (2) held at 55 °C (5, 10, and 30 min), and (3) held at 70 °C (5, 10, and 30 min). Seeds were treated (50 seeds per treatment) and then placed aseptically in 1.5% water agar in a Petri dish. We recorded the percentage of seeds from which fungi were growing after 3 days and the percentage of seeds that had germination after 7 days. The seed of origin of fungal growth could not be reliably determined after 3 days, and percent germination did not meaningfully increase after 7 days.
We compared the mean outcomes of each treatment to that of the control treatment (sterile deionized water) using a Dunnett test (DescTools package in R). A Wilcoxon paired rank test (wilcox.text, stats package in R) was used to test whether sonication significantly affected the effectiveness of the disinfectant treatments (boiling was excluded from this analysis because there was no sonication for that treatment).