Impacts and Use of Sub-zero Temperatures During Cut Flower Production and Postharvest Handling
Nathan Jahnke, Ph.D. Final Seminar
Under the direction of Dr. John Dole and Dr. David Livingston
Wednesday, June 17, 2020, at 10:00 am
Join Zoom Meeting:  https://ncsu.zoom.us/j/95569991034?pwd=R2M1VEkxOHh2K05HakFFcm1CeXViZz09
Meeting ID:  955 6999 1034

Abstract
Sub-zero temperatures are often avoided during the production and postharvest handling of perishable cut flowers due to the potential of freezing and injury. However, previous research suggested that using sub-zero temperatures during storage could have a positive effect on the subsequent vase life and quality of cut flowers. Storage is a vital component of the cut flower supply chain because it allows for season extension of species with constricted production, flexibility in product supply, and potentially reduces production costs. Primarily, cut Paeonia lactiflora Pall. (peony) hybrids were used to explore the use of sub-zero temperatures for long-term storage due to their high value, seasonal but worldwide production, and tolerance to sub-zero temperatures and dry storage. Freezing was confirmed using infrared cameras and cut peonies were uninjured when stems were held -2 °C for 5 h. Using a storage temperature of -0.6 °C, there was a small improvement of cut peony vase life when compared to stems stored at the industry standard temperature of 0.7 °C. Quality of dry-stored cut peonies was higher in stems stored at -0.6 °C as determined by a decrease in the number of peony flowers that failed to open, a decrease in flower deformities, larger flower diameters, and a decrease in disease incidence. Storage life was extended to an unprecedented 16 weeks with minimal impact on the vase life following storage. In a cooperative study with Washington State University, a sub-zero temperature of -1 °C minimized the development of Botrytis cinerea, a ubiquitous fungal pathogen, on cut peonies following long-term storage and shipment of stems to North Carolina State University. Sub-zero temperature storage was tested on cut Tulipa (tulips) and Iris × hollandica (Dutch iris) stems in conjunction with various other postharvest handling techniques. Three improved handling methods were developed leading to a storage life of 6 weeks for tulips and improved quality of Dutch iris following storage at -0.6 °C. Finally, sub-zero temperatures were used to simulate spring freeze events on whole plant peonies providing preliminary data on peony bud tolerance to freezing temperatures during production. These studies provide crucial data capable of improving postharvest handling guidelines of cut flowers using sub-zero temperatures while providing insight on cut flower phenology and physiology.