Bases structurales et biochimiques de la résistance au gui dans le genrePopulus

Abstract

Summary In the poplar/mistletoe association, the resistance phenomenon was investigated using histochemistry, histofluorescence and analytical methods. Among the six poplar cultivars tested, the cv. “Fritzi Pauley” was sensitive, the cvs “Blanc de Garonne”, “Vereecken” and “Italica” were totally resistant whereas the cvs “1214” and “Bergerac” were intermediate. The different responses of these cvs. to mistletoe occurred 10 months approximatively after the beginning of the artificial infestation. Resistant cvs developed successive inner periderms. The last one could not be passed through by the growing primary haustorium. In the perihaustorial zone delimited by the inner periderm and the haustorium, a large amount of polyphenols accumulated. Their taniferous and flavonoidic nature was established by histochemistry, histofluorescence and thin layer chromatography. In the sensitive cv., the peridermic reaction was so weak that the inner periderm was rapidly torn out, allowing a rapid growth of the haustorium through the host tissues. In non parasitized poplar branches, the nature and the amount of preexisting phenols turned out to be two basic parameters highly involved in the phenomenon of resistance.