| Abstract
| - Cultivated and wild species of the genus Vigna were screened for their flavonoid content. FlavonoidHPLC analyses clearly showed that cultivated lines of cowpea (Vigna unguiculata L. Walp.) arevery similar from a qualitative point of view, always showing three flavonoid aglycons: quercetin,kaempferol, and isorhamnetin. In addition, a positive relationship between resistance/susceptibilitycharacteristics against aphids and flavonoid glycoside content of cowpea lines was found. Theresistant lines showed a flavonoid content higher than that of susceptible ones. In vitro bioassaysproved that, among endogenous flavonoids, quercetin and isorhamnetin possess a good inhibitoryaphid reproduction rate. Flavonoid HPLC analyses of wild Vigna species supported evidence forthe existence of different flavonoid chemotypes in some species of section Vigna. There are kaempferolchemotypes, kaempferol being the main aglycon detected, quercetin chemotypes, containing quercetinglycosides only, and two isorhamnetin chemotypes. When the resistance characteristics to aphidsin different chemotypes of the same species were tested, it became evident that quercetin orisorhamnetin chemotypes showed a higher level of resistance compared to kaempferol chemotypesin the same species, thus demonstrating a direct involvement of quercetin or isorhamnetin in theresistance mechanism. These results can provide useful information for further studies on geneexpression of resistance factors. Keywords: Plant phenolics; flavonoids; bioassay; aphid resistance; Vigna species
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