Suppression of Verticillium dahliae by glucosinolate-containing seed meal amendments

Abstract

The biofumigation potential of glucosinolate (GSL)-containing seed meals to Verticillium dahliae was systematically evaluated. Cultivars of four different species of Brassicaceae were assessed using a standardized bioassay with microsclerotia-infested sterile quartz sand amended with defatted seed meals at a rate of 0.4 % (vol/vol). Additionally, the GSL profile and isothiocyanate (ITC) release of the meals were determined. Brassica napus and Sinapis alba seed meals failed to reduce the number of viable microsclerotia significantly due to low concentrations and/or toxicity of the ITCs released. Amendments with B. juncea and B. carinata seed meals eliminated all microsclerotia in the sterile sand. The meals had 2-propenyl GSL concentrations between 82.8 and 108.1 μmol g−1. ITC release efficiencies ranged between 62.5 and 100 %. The expected amounts of 2-propenyl ITC released by the amendments suggest that the elimination of microsclerotia by the sinigrin-containing seed meals was predominantly an ITC-related effect. But in natural infested soils the efficiencies of B. juncea seed meal amendments were reduced. Depending on soil characteristics practical meal amendment rates of 4.0 t ha−1 or higher may be necessary to achieve sufficient Verticillium control. Additionally, the temporal pattern of ITC release of the amended B. juncea seed meal in two natural soils compared to sterile sand was determined. Maximum ITC concentrations were measured between 3 and 6 h after application, before concentrations decreased continuously and reached a minimum after 48 h. In summary, the findings suggest that sinigrin-containing seed meal amendments can be a useful tool in the management of Verticillium, especially on sandy soils with low organic carbon contents.