POLYPHENOLS AND RESISTANCE OF POPLAR (POPULUS SPP.) TO MISTLETOE (VISCUM ALBUM L.)

Flavonoid compounds were studied in healthy and parasitized poplar branches following mistletoe attack (Viscum album L.). Four poplar cultivars showing different degrees of resistance to mistletoe were used : "Fritzi Pauley", FPL, sensitive ; "Vereecken", VER, "Blanc de Garonne", BDG, and "Italica", ITA, resistant ones.
Flavonoids were specifically detected and localized by histofluorescence after treatment of frozen sections by Wilson’s reagent.
Their total amounts were estimated in non-parasitized branches by spectrophotometry whereas their chemical nature was determined by thin layer chromatography.
These investigations indicated that non-parasitized branches of resistant cultivars were enriched in flavonoid compounds, i.e. flavonols, flavones and flavanones as compared to the sensitive one, FPL.

Induced mechanisms of defence appeared during the primary haustorium penetration.
They consisted of numerous inner periderm development and flavonoid accumulation.
These reactions were much more weaker in the FPL cultivar than in the resistant ones, VER and BDG. In the resistant cultivars, the growth of the primary haustorium and the establishment of direct connections between the host living cells and the parasite failed.
The resistance of poplar cultivars to mistletoe involved, at least, two types of barriers: a chemical barrier (the polyphenolic synthesis) and mechanical ones (thickness of phellem, fibers and inner phellems).

International Symposium on Natural Phenols in Plant Resistance

G.C. Sallé, E.B. Hariri, C. Andary

https://doi.org/10.17660/ActaHortic.1994.381.109