Influence of PAR flux and temperature on the flower bud abortion of rose (Rosa hybrida cv. Frisco) and the carbon balance of the shoot

The occurrence of flower bud abortion for rose, especially during winter, is attributed to a disequilibrium between the carbohydrate production in the sources and the demand for the assimilates in the sinks, caused by a low light intensity or a limitation of the translocation pattern. Manipulating the source and the sink strength by the light intensity and the translocation by temperature may lead to a reduction of flower abortion and an improved flower stem quality. An experiment was set up for roses (cv. Frisco) in 3 growth chambers of the Laboratory of Plant Ecology, including a control treatment (day/night temperature of 18116 degrees C and 300 mu mol-PAR), a low night temperature combined with high light intensity (18/12 degrees C; 300 mu mol PAR) and a low night temperature and low light intensity (18/12 degrees C; 100 mu mol-PAR). Measurements of the photosynthesis rate at shoot level (for a shoot length of 6 cm, 10 cm and 15 cm) and the carbohydrate content of several plant parts (also for different shoot lengths, corresponding with different developmental stages of the apex), as well as observations of the degree of abortion and the flower stem quality were performed. From the results, it was shown that the treatments influenced the rate of development of the shoot. The low night temperature, combined with the non-limiting light intensity enhanced the quality of the flower stem and decreased the abortion rate. Moreover, for a shoot length of ca. 10 cm (the critical stage of flower bud abortion), the quantum efficiency of the shoot and the carbohydrate content of the most mature leaf on the shoot were significantly higher than in the other treatments. The results support that a sufficient supply of carbohydrates during the critical stage for abortion, in combination with a high light intensity, which is known to enhance the sink strength, leads to a reduction of flower abortion and better flower stem quality.