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 Cara Mia (trade name as officially registered cultivar name). Unlike flowers on plants in greenhouses, cut flowers placed in water in 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 and the time to petal abscission was as in uncut flowers. In Sonia roses the symptoms of water stress varied from mild to severe, and the number of flowers in which the petals abscised varied from 100% (mild stress) to 0% (severe stress). An antimicrobial compound in the vase water of Sonia roses, or removal of the leaves, alleviated the symptoms of water stress and increased the number of stems in which the petals abscised. Cut Cara Mia roses showed severe symptoms of water stress in all experiments and petal abscission was found in only a few flowers, even when the stems were placed at 20 °C and low photon flux (15 μmol m-2 s-1). Abscission in Sonia and Cara Mia roses was low or absent when the water potential of the leaves reached values below -2.0 MPa within the first 5 d of the experiment; such low values were not reached in Frisco roses. Addition of sucrose to the vase solution, together with an effective antimicrobial compound, had no effect on the time to petal abscission, at any light intensity. Placing flowers in far- red light also had no effect on abscission, compared with flowers placed in red light or white light of the same photon fluence. It is concluded that petal abscission in the rose cultivars studied is not affected by their water status unless the plants reach a low water potential (about -2 MPa) early on during vase life. Petal abscission is not inhibited by low light intensity nor affected by the Pr/Pfr ratio