A Simple Analytical Method for Dhurrin Content Evaluation in Cyanogenic Plants for Their Utilization in Fodder and Biofumigation

Cyanogenic plants have some potential as biocidal green manure crops in limiting several soilborne pests and pathogens. Sorghum (Sorghum bicolor (L.) Moench) and Sudangrass (Sorghum bicolor subsp. sudanense (P.) Stapf), in fact, contain the cyanogenic glucoside p-hydroxy-(S)-mandelonitrile-β-d-glucoside (dhurrin) as a substrate of its secondary defensive system able to release hydrogen cyanide following tissue lesions due to biotic or abiotic factors. Given that dhurrin content is correlated with the biofumigant efficacy of the plants, a high dhurrin content could be a positive character for utilization of sorghum and Sudangrass as biocidal green manure plants. For chemical characterization of the available germplasm, a simple, safe, and accurate method is necessary. In this paper, a new method for dhurrin analysis, based on methanol extraction and high-performance liquid chromatography, is reported and discussed. The feasibility of this analytical procedure was tested by evaluating dhurrin level in roots and stems during cultivation of four different sorghum and Sudangrass varieties in agronomic trials performed in 2008 in the Po valley (Italy). The dhurrin content ranged from 0.16 ± 0.04 to 7.14 ± 0.32 mg g–1 on dried matter (DM) in stems and from 1.38 ± 0.02 to 6.57 ± 0.09 mg g–1 on DM in roots, showing statistical differences among the tested germplasms that could be linked to the efficacy of their utilization as biofumigant plants. The method also opens new perspectives for the characterization of sorgum plants as fodder, for which the presence of dhurrin is considered to be negative for its well-known toxicity.