Petal Abscission in Rose Flowers: Effects of Water Potential, Light Intensity and Light Quality

Petal abscission was studied in roses (Rosa hybrida L.), cvs.Korflapei (trade name Frisco), Sweet Promise (Sonia) and CaraMia (trade name as officially registered cultivar name). Unlikeflowers on plants in greenhouses, cut flowers placed in waterin the greenhouse produced visible symptoms of water stress,depending on the weather during the experiment and on the cultivar.Cut Frisco roses showed no visible signs of water stress andthe time to petal abscission was as in uncut flowers. In Soniaroses the symptoms of water stress varied from mild to severe,and the number of flowers in which the petals abscised variedfrom 100% (mild stress) to 0% (severe stress). An antimicrobialcompound in the vase water of Sonia roses, or removal of theleaves, alleviated the symptoms of water stress and increasedthe number of stems in which the petals abscised. Cut Cara Miaroses showed severe symptoms of water stress in all experimentsand petal abscission was found in only a few flowers, even whenthe stems were placed at 20 °C and low photon flux (15 µmolm^-2s^-1). Abscission in Sonia and Cara Mia roses was low or absentwhen the water potential of the leaves reached values below-2.0 MPa within the first 5 d of the experiment; such low valueswere not reached in Frisco roses. Addition of sucrose to the vase solution, together with an effectiveantimicrobial compound, had no effect on the time to petal abscission,at any light intensity. Placing flowers in far-red light alsohad no effect on abscission, compared with flowers placed inred light or white light of the same photon fluence. It is concluded that petal abscission in the rose cultivarsstudied is not affected by their water status unless the plantsreach a low water potential (about -2 MPa) early on during vaselife. Petal abscission is not inhibited by low light intensitynor affected by the Pr/Pfr ratio. Abscission; light intensity; petals; phytochrome; Rosa hybrida L.; rose; sugars; water potential