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Seven resistant varieties of sweetpotato were compared with three susceptible varieties in field trials and laboratory bioassays and showed that resistance was an active process rather than an escape mechanism, as field resistant varieties also had reduced root damage and oviposition compared with susceptible varieties in the laboratory. Liquid chromatography-mass spectrometry (LC-MS) of root surface and epidermal extracts showed significant variation in the concentration of hexadecyl, heptadecyl, octadecyl, and quinic acid esters of caffeic and coumaric acid, with higher concentrations correlated with resistance. All compounds were synthesized to enable their positive identification. Octadecyl coumarate and octadecyl caffeate applied to the surface of susceptible varieties in laboratory bioassays reduced feeding and oviposition, as observed on roots of resistant varieties, and therefore are implicated in weevil resistance. Segregating populations from breeding programs can use these compounds to identify trait loci for resistance and enable the development of resistant varieties.

Securidaca longepedunculata Fers (Polygalaceae) is commonly used as a medicine in many parts of Africa and shows promise for protecting stored grain against insect pests. Analysis of a methanol extract of the root bark by gas chromatography linked to mass spectrometry (GC/MS) showed a major component accounting for over 90% of the volatile material. This was identified as methyl 2-hydroxybenzoate (methyl salicylate) by comparison of the GC retention times and mass spectrum with those of synthetic standards. This conflicts with an earlier report that the major component is methyl 4-hydroxybenzoate. Two minor components had mass spectra characteristic of 2-hydroxybenzoate esters and were identified as methyl 2-hydroxy-6-methoxybenzoate and its benzyl analogue, again conflicting with an earlier report., (Copyright 2002 John Wiley & Sons, Ltd.)