Abstract The aim of this work was to determine the basis of resistance in a sub-Saharan sweetpotato variety, New Kawogo, to the African sweetpotato weevil Cylas puncticollis. This insect feeds on the roots, reducing quality and yield, and is the most important production constraint of sweetpotato in Africa. Laboratory bioassays were designed to determine how the performance of weevils differed on susceptible and resistant roots. Subsequently, liquid chromatography-mass spectrometry (LC-MS) analysis of the root surface and root latex identified quantitative and qualitative differences in the chemical profiles with higher levels of octadecyl and hexadecyl esters of hydroxycinnamic acids reported in the resistant variety. The compounds were synthesized to confirm their identity and incorporated into artificial diets for bioassays on C. puncticollis. High levels of mortality and developmental inhibition were recorded for larvae feeding on treated diets, and the effect was dose-dependent. Thus, in contrast to previous work on resistant African sweetpotato cultivars, resistance in New Kawogo is not only active, but is quantifiable and manageable for breeding. Work is underway to determine what effect these compounds have on the weevils at a molecular level. The inheritance of the root latex esters will be studied in new crosses and mapped in new populations using quantitative trait loci (QTLs) that are currently being developed.
Atmospheric pressure chemical ionisation (APCI) and electrospray (ES) are compared as ion sources in the analysis of polyhydroxyalkaloids (PHAs) by liquid chromatography mass spectrometry (LC-MS) and collision induced dissociation (CID) product ion spectra, from tandem mass spectrometry (MS-MS) experiments in a quadrupole ion trap, are reported for 12 naturally occurring PHAs. APCI was found to be a more useful source than ES, as APCI could be used to generate deprotonated molecule ions in negative mode and for some isomeric PHAs the negative CID product ion spectra were more diagnostic than the positive product ion spectra. On-column detection limits were also approximately 32 times lower by positive APCI than ES. The work provides data that will facilitate screening and characterisation of this group of important natural products in plant and fungal extracts.
Oral treatment of mice, cutaneously infected with herpes simplex virus type 1 (HSV-1) (strain SC16), with the α-gluco-sidase 1 inhibitor 6-O-butanoyl castanospermine (MDL 28,574) produced a significant delay in lesion development and reduced the amount of virus recovered from the brain. Virus load in the brains of mice, whose treatment started 2 days prior to infection, was reduced ˜100-fold when compared to untreated controls. Treatment initiated at the time of infection, while less effective than pre-treatment, nevertheless reduced virus recovery from the brain by 10-fold. Consistent with its antiviral activity, orally administered MDL 28,574 was rapidly incorporated by brain tissue and mice fed with compound over extended periods maintained relatively high levels of drug at this site.
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