Water relations of cut roses as influenced by vapor pressure deficits and temperatures

Abstract

Freshly harvested 'Bridal Pink' roses (Rosa hybrida L.), with their stem bases in test tubes containing deionized water, were placed in a glass tank and held in a controlled environment room at 14, 20, or 30 °C. The vapor pressure deficit (VPD) in the tank was maintained at nearly 0 kPa (no VPD: NVPD) or 0.9 kPa (intermediate VPD: IVPD). At all temperatures and VPDs, the fresh weight of cut roses increased initially and then decreased; the decrease occurred earlier in IVPD than in NVPD and at higher temperatures. Necks of all flowers placed in IVPD became bent within 48, 144, and 312 hr of postharvest at 30, 20, and 14 °C, respectively; whereas, bent neck did not develop in NVPD. Irrespective of temperature, transpiration and water uptake rates of the roses placed in IVPD were markedly higher than those in NVPD. In IVPD, these rates increased initially, but decreased after 48, 72, and 96 hr at 30, 20, and 14 °C, respectively. Petal water potential gradually decreased during the first 36 hr at 30 °C in IVPD, but did not change at 14 °C. The osmotic potential increased with time and was higher at 30 °C than at 14 °C. Fructose, glucose, and sucrose were the major sugars in petals. Concentrations of these sugars decreased during the first 36 hr, the decrease being greater at 30 °C than at 14 °C. The contribution of these sugars to the petal osmotic potentials was only 10%. These data indicate that the water relations of cut roses, immediately after harvest, was greatly influenced by high VPD by hastening the transpiration rate, and subsequently by increasing temperature through rise in the osmotic potential which was partly attributable to the consumption of respiratory substrate.