Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/31/2013
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Plants from the Brassica family contain glucosinolate-derived compounds (GDC) which may act as natural antimicrobials in soil. Consequently, Brassica cover crops planted after harvest of the primary crop in the fall, and/or ntercropped during the growing season, could provide benefits derived from secreted antimicrobial compounds, released during plant growth but primarily at the time of residual corporation (till over). The antimicrobial effect of various GDC: isothiocyanates, isothiocyanates, indole methyl oxazolidinone, and methyl propyl pyrazole carboxylic acids against E. coli O157:H7 and Salmonella was determined. Sterile filter disc (6 mm) impregnated with 10-20 µL of GDC (10 mg/ml) were placed on Tryptic soy agar (TSA) plates seeded with the respective pathogen. After 48 h incubation at 37°C, the inhibitory zone (mm) around the disc was recorded. In general, Salmonella was more sensitive to these GDC than E. coli O157:H7, while benzyl isothiocyanate (BIT) exhibited the strongest antimicrobial activity as observed by the disc diffusion assay. A field study was conducted to evaluate the antimicrobial affects of broccoli. Six-week old broccoli seedlings (Packman cultivar) were planted in a 1/2 acre field. After reaching full maturity, broccoli florets were harvested and the remaining plants were tilled over with a tiller set at 4 in depth. The tilled over soil was sprayed with a non-pathogenic E. coli O157:H12 strain (7 log CFU/ml, 1 L per 25 sq ft) enriched in fecal slurry. Soil samples were analyzed periodically for surviving populations of E. coli O157:H12 using spiral plating on selective media and by Most Probable Number (MPN) enrichment procedures. Populations of E. coli O157:H12 decreased gradually in soil with time. At 28 days after inoculation, E. coli O157:H12 were significantly lower in broccoli-tilled soil than in the control soil. Broccoli cultivars (Arcadia, Bellstar, and Diplomat) grown in the greenhouse were harvested into three fractions (roots, leaves and stems, and florets) and freeze dried. Qualitative evaluation of intact glucosinolate in these fractions was conducted using HPLC and mass spectrometry. Glucotraopaeolin was higher in roots of Diplomat and Bellstar cultivars whereas sinigrin content was higher in roots of the Arcadia cultivar. These results indicate that Brassica plants can be used as a cover crop (green manure) to effectively control enteric pathogens in soils.