Chemical components of the Brassicaceae that suppress plant-parasitic nematodes

Isothiocyanates are released through enzymatic degradation of glucosinolates produced by plants in the Brassicaceae. Glucosinolate profiles differ among plant species and the isothiocyanate derivatives differ in their toxicity to nematodes. Field experiments conducted in California demonstrated that the control of plant-parasitic nematodes in soil by isothiocyanates released from incorporated brassicaceous plant material can be unpredictable. Success might be improved with a better understanding of the chemical components of the Brassicaceae responsible for nematode suppression. A stepwise and iterative experimental process was developed to improve the effectiveness of using the Brassicaceae for nematode management. Laboratory assays were conducted to determine lethal concentration values of commercially-available isothiocyanates against Tylenchulus semipenetrans and Meloidogyne javanica. Isothiocyanates varied greatly in their toxicity towards the plant-parasitic nematodes with benzyl and 2-phenylethyl isothiocyanates, and to a lesser extent allyl isothiocyanate, being the most toxic. Tylenchulus semipenetrans was more sensitive than M. javanica to most of the tested isothiocyanates. In subsequent laboratory experiments, plant materials, containing glucosinolate-precursors to the most toxic isothiocyanates to M. javanica and T. semipenetrans , were selected and applied based upon isothiocyanate lethal concentration values. Glucosinolate profiles, in combination with isothiocyanate lethal concentration values, were reliable and repeatable basis for application rates of Brassica hirta for both nematodes and B. juncea for M. javanica. These same factors underestimated additions rates of B. juncea. Major contributors to nematode suppression were: glucosinolate to isothiocyanate conversion rates, the distribution of amendment material in the soil profile, and potentially anaerobic conditions in the soil created by plant biomass. Application of brassicaceous amendments for plant-parasitic nematode management initiates dynamic and complex biological and chemical processes. Despite this inherent complexity, we find that brassicaceous amendments can be applied for consistent and repeatable nematode suppression when based upon the chemistry of the incorporated material.