SUPPRESSION OF BOTRYTIS BLIGHT IN ROSE FLOWERS WITH GIBBERELLIC-ACID - POSSIBLE FORMATION OF ENDOGENOUS INHIBITORY COMPOUNDS

Elongation of conidial germ tubes as well as linear growth of colonies of the fungal pathogen Botrytis cinerea were inhibited when growth me dia in vitro were supplemented with leachates from GA(3)-treated petal s of-rose (Rosa x hybrida cv. Mercedes) flowers. Content of phenylic s ubstances extracted from petals 6 days after the GA(3) treatment was h igher than that in the control petals whereas no differences in conten t of phenols were found between the GA(3)-treated and the control peta ls examined 8 days after the GA(3) treatment (9 days after harvest). S pore germination, germ tube elongation and mycelium growth were also i nhibited when growth media in vitro were supplemented with phenolic ex tracts from petals treated with GA(3) 6 days prior to extraction but n ot when they were extracted 8 days after the GA(3) treatment. Botrytis blight development in vivo was almost completely inhibited by phenoli cs extracted 6 days after GA(3) treatment and was also practically inh ibited by extracts From older petals. The content of sugars and amino acids in leachates from GA(3)-treated petals was lower than that in le achates from control petals. The inhibition of germ tube elongation in leachates from GA(3)-treated petals was eliminated when the growth me dia were supplemented with excessive amounts of-glucose. The inhibitio n of Botrytis blight development in GA(3)-treated flowers in vivo was also eliminated when conidial suspensions were supplemented with gluco se. The possible GA(3)-imposed formation of inhibitory compounds with a phenolic moiety is discussed.