Physiological responses of garden roses to hot and humid conditions

Garden roses do not grow well under hot and humid conditions. The objective of this study was to investigate the physiological responses of 'Marie Curie' and 'Lapjau' to high temperatures and relative humidity. The study included temperatures of 25/18 degrees C (day/night) and 35/28 degrees C (day/night), and relative humidity of 70% and 100%. 'Marie Curie' was more tolerant to heat stress than 'Lapjau' based on relative electrolyte leakage (REL), malondialdehyde (MDA), and activities of superoxide dismutase (SOD). The heat tolerance of cultivars also was confirmed by the levels of chlorophyll content and the net photosynthesis rate. Both cultivars were more stressed under more water vapour deficit than saturated vapour at 35/28 degrees C (day/night), while at 25/18 degrees C (day/night) the cultivars were more stressed under saturated humidity condition than at 70% relative humidity. In conclusion, combined hot and saturated humidity does not necessarily result in increased stress over separated heat or humidity elevations to the garden roses. Rose growers can use this information in regions where hot and humid conditions concur.