Exploring the Soil Myrosinase-Glucosinolate System in Plant Protection.

Biofumigation using glucosinolates (GSLs) can suppress soil-borne pests due to the biofumigant properties of the highly toxic isothiocyanates present in Brassica vegetables. The objectives of this investigation were to: 1) assess variation in total GSLs concentrations among collard plants grown under three soil management practices: sewage sludge (SS) mixed with native soil, chicken manure (CM) mixed with native soil, and no-mulch (NM) native soil used for comparison purposes, and 2) quantify GSLs concentrations in collard roots, leaves, and stems. Separation of total GSLs was accomplished by adsorption on DEAE-Sephadex ion exchange resin of 40-125 µm bead size using disposable pipette tips filled with DEAE that has a net positive charge when ionized and therefore bind and exchange anions (anion-exchange resin). Quantification of total GSLs was based on inactivation of plant endogenous myrosinase and liberation of the glucose moiety from the GSLs molecule by addition of standardized myrosinase and colorimetric determination of the liberated glucose moiety. Across all treatments, SS and CM increased soil organic matter content from 2.2% in native soil to 4.2 and 6.5%, respectively. GSLs concentrations were significantly greater in collard leaves (30.9 µmoles g^-1 fresh weight) compared to roots and stems (7.8 and 1.2 µmoles g^-1 fresh weight, respectively). Collard grown in soil amended with SS contained the greatest concentrations of GSLs compared to CM and NM treatments. Accordingly, leaves of collard plants grown in soil amended with SS could play a significant role in sustainable agriculture as alternative tools for control of soil-borne diseases.  In addition, soil amendments might reduce the biomass needed to produce significant concentrations of isothiocyanate-generating GSLs in Brassica plants for greater fumigant potential.