Prohexadione-Ca application modifies flavonoid composition and color characteristics of rose (Rosa hybrida L.) flowers

The effect of foliar application of prohexadione-calcium (ProCa) on the expression of color and the content of secondary metabolites was observed in two rose cultivars: an orange-red cultivar ‘KORcrisett’ and a dark red cultivar ‘KORikis’. The study aims to describe the induced accumulation of specific flavanones in rose by ProCa sprayings and the effects on the content levels of major flavonoids and anthocyanins in rose petals important for their ornamental value. Plants were sprayed once with 300 ppm Regalis® solution in bi-distilled water and the control plants with bi-distilled water only. Color parameters were colorimetrically evaluated, and individual phenolic compounds were identified with the use of HPLC–MS. A significant visual change in red petal coloration was observed and recorded as a decline of the color parameter a* after the application of Regalis® on day 9 and particularly on day 15. Similarly, lightness (L*) increased and chroma (C) decreased in both analyzed cultivars as expected in paler petals. The content of major anthocyanins in rose petals, cyanidin-3,5-di-glucoside, pelargonidin-3,5-di-glucoside, cyanidin-3-glucoside, pelargonidin-3-glucoside and peonidin-3-glucoside, was drastically reduced after Regalis® application in both analyzed roses. Also, the content of quercetin and kaempferol compounds generally decreased to the point of detection; however, newly formed eriodictyol was identified in the petals of the treated ‘KORikis’ flowers 15 days after application and in the petals of ‘KORcrisett’ flowers 9 and 15 days after application. Foliar application of ProCa thus altered visual properties of red rose flowers, which has been directly correlated to the content of anthocyanins, and also induced the formation of 3-deoxyflavonoids, normally not present in roses under natural conditions. Different shades of red and light pink flowers were present on a single rose plant which can potentially present an interesting marketable product for the consumers.

► Color changes of rose flowers due to prohexadione-Ca application.
► Decrease in individual and total anthocyanin content levels.
► Phase-dependant effect of prohexadione-Ca foliar application.
► Temporal effect on color and phenolic composition.