Impacts of carbohydrate pulses and short-term sub-zero temperatures on vase life and quality of cut Paeonia lactiflora Pall. hybrids

Authors: JAHNKE, NATHAN - North Carolina State University; DOLE, JOHN - North Carolina State University; Livingston, David; BERGMAN, BEN - North Carolina State University

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2019
Publication Date: 12/30/2019
Citation: Jahnke, N., Dole, J., Livingston, D.P., Bergman, B. 2019. Impacts of carbohydrate pulses and short-term sub-zero temperatures on vase life and quality of cut Paeonia lactiflora Pall. hybrids. Postharvest Biology and Technology. https://doi.org/10.1016/j.postharvbio.2019.111083.
DOI: https://doi.org/10.1016/j.postharvbio.2019.111083

Interpretive Summary: Peony is an important plant for the cut-flower industry. Extending the longevity of the cut flower can increase the value of the plant for growers. We subjected cut flowers to temperatures below zero to see if they would be damaged and to see if we could extend the life of the flower. In addition we pulsed the stems with sugar solutions to see if sugars pulled up by the stems would reduce the freezing point of the flower. Stems were frozen in a controlled environment freezer and monitored with an infrared camera to confirm (or not) that stems had frozen. Pulsing the plants with sugars had no effect on freezing point or longevity of the flower. Stems frozen to -4C showed some damage and the longevity of the flowers were reduced. However, stems frozen at -2C showed no damage even though infrared analysis indicated that stems had frozen. This suggests that storage temperatures below zero (but not as cold as -4C) would be a good option to extend the life of peony flowers.

Technical Abstract: Flower quality of cut Paeonia lactiflora (peony) Pall. hybrids is best preserved between 0 and 1 °C. However, cut flower traits such as vase life and flower size often decline following 4 or more weeks of storage. While the use of sub-zero temperatures is avoided in the cut flower industry due to fears of freeze injury, sub-zero temperatures may allow extended storage of cut flowers. Peonies are a candidate for sub-zero storage due to their natural cold tolerance, exposure to spring freezes before harvest, and limited seasonal availability. Three cultivars: Karl Rosenfield, Monsieur Jules Elie, and Sarah Bernhardt were used to evaluate freeze tolerance of cut peonies by holding cut stems at three temperatures: 0, -2, -4 °C for 5 h. Pre-cold treatment pulses consisting of 24 h in either 100 g·L-1 sucrose, 100 g·L-1 fructose, or tap water did not improve total vase life, summation of the time spent as a bud and time open. Total vase life was 10.5, 7.1, and 9.3 d for ‘Karl Rosenfield’, ‘Monsieur Jules Elie’, and ‘Sarah Bernhardt’, respectively. Sucrose-pulsed stems of ‘Karl Rosenfield’ and ‘Sarah Bernhardt’ had the lowest total vase life. Pulses and cold-treatments decreased bud time for ‘Karl Rosenfield’ and ‘Monsieur Jules Elie’ by 2 to 3 d and 0.5 to 1 d, respectively. Petals were the only tissue to develop water-soaked spotting (freeze injury) following 5 h at -4 °C. Stems kept dry (not pulsed) prior to cold treatment were uninjured. Fructose-pulsed stems of ‘Karl Rosenfield’ and ‘Monsieur Jules Elie’ had the highest injury ratings when held at -4 °C. Carbohydrate -pulsing did not influence injury ratings on ‘Sarah Bernhardt’. Supercooling and multiple freeze events were observed with infrared video in all tissues when held at -4 °C. Typically, ice nucleation started at the base of the cut stems and propagated throughout the stem, leaves, and bud within 3 to 5 min of initiation. Stems that were not pulsed remained in a supercooled state longer than those that were pulsed. These findings indicate that storage temperatures between 0 and -2 °C may be a good option for longer periods of dry storage for peonies and other cold tolerant cut flower species.