Improving media pH Management by Developing a Model of the Interacting Factors in the pH System
Dr. Paul Fisher, University of New Hampshire, $20,000
Annual Progress Report
June 1, 2006
James E. Faust, Scott Whiteside, and Kay Cooksey
Clemson University
John M. Dole and Sylvia M. Blankenship
North Carolina State University
Industry Needs Addressed.
Current shipping procedures require that cuttings be harvested from the stock plants in Mexico, Guatemala, Costa Rica, Columbia, Kenya, Israel and China and delivered to customers in the United States within 48 to 72 hours. Significant losses occur annually due to damage or death of cuttings in transit and poor cutting performance after receipt. These losses negatively affect both the suppliers and the grower customers.
We are studying the effects of the post-harvest environment on the longevity of unrooted cuttings. Our objectives are to: 1) understand the basic physiology of unrooted cuttings, e.g., effects of temperature on respiration rates, ethylene production rates and ethylene sensitivity. 2) determine the potential benefits of modified atmospheres on cutting longevity, e.g., high carbon dioxide and low oxygen environments. 3) design and develop packaging materials and methods that provide the optimum post-harvest environment and atmosphere. 4) evaluate the feasibility of applying modified atmosphere packaging to the storage and/or shipping of unrooted cuttings.
The results of this project will have the following impacts: 1. We will develop “best management practices” for the shipment of unrooted cuttings. These practices include environmental management and package design. The result will be an improvement of cutting survival during shipment and a reduction in subsequent crop losses in propagation. 2. We will identify the limits of unrooted cutting longevity. This will provide growers with the knowledge required to make decisions to improve the economics of harvesting, storing and shipping unrooted cuttings. 3. We will identify potentially improved materials and methods used for packaging, storing and shipping unrooted cuttings. 4. We will determine the cause of various physiological disorders. The array of post-harvest treatments provided during these experiments will allow us to document the symptoms and causes of a wide array of physiological disorders of unrooted cuttings, which will aid in the diagnosis of problems that occur during shipping and storage.
Summary of Work Completed.
Identifying optimal storage temperatures and durations.
Unrooted poinsettia ‘Prestige’ cuttings were placed in plastic bags and stored at 0, 5, 10, 15, 20, and 25°C for 0, 2, 4, 6, 8, 10, 12, and 14 days. Cuttings were evaluated upon removal from storage and again after 3 weeks in propagation. The optimal storage temperature for poinsettia cuttings was between 10 and 15°C. Cuttings could be stored between 10 and 15°C for 10 days without serious detrimental effects on either shoot appearance or rooting performance in propagation. Temperatures above and below this temperature range significantly shortened storage life by approximately half. Cuttings stored at cooler temperatures (≤ 5°C) had chilling damage. Cuttings stored at warmer temperatures (≥ 20°C) dehydrated in storage. Optimal storage temperatures and durations have also been identified for dahlia, diascia, geranium, double impatiens, New Guinea impatiens, lantana, lavender, perilla, and portulaca unrooted cuttings.
Measuring the respiration rates (CO2 production) and ethylene production rates of unrooted cuttings at constant temperatures. Unrooted poinsettia ‘Prestige’ cuttings were placed at 5, 10, 15, 20, and 25°C. Respiration rates were evaluated at 2, 6, 10, 24, 48, and 72 hours of storage. After 72 hours, cuttings were propagated and evaluated after 3 weeks in propagation. As storage temperature increased, respiration rates increased. Respiration rates declined rapidly over the first 24 hours for cuttings stored at 20-25°C. Cuttings stored at 5-10°C had fairly constant respiration rates over the entire storage duration. By 24 hours, all respiration rates were relatively constant and did not vary between storage temperatures.
Respiration rates are also an indication of carbohydrate depletion in the cuttings. Depletion of carbohydrate levels below a minimum threshold could have implications on success in propagation (e.g., delayed rooting). No significant differences (after 72 hours in storage) were observed for cuttings stored at 5, 10, 15, and 20°C. However, cuttings stored at 25°C for 72 hours were below acceptable quality following 3 weeks in propagation. Respiration rates at constant temperatures have also been determined for New Guinea impatiens, double impatiens, and petunia cuttings.
Ethylene production rates were measured during storage. At warm storage temperatures (20-25°C), ethylene accumulates quickly in the plastic bags resulting in cutting deterioration, i.e., leaf yellowing and abscission. At cooler storage temperatures (10-15°C), accumulation of ethylene is slower, and cuttings can be held for a long duration without detrimental effects. For New Guinea impatiens, a chilling-sensitive species, ethylene production increased when cuttings are stored at damaging cold temperatures, e.g., <7.5°C. Ethylene production rates have also been determined for lantana, poinsettia, and portulaca unrooted cuttings.
Interaction of carbohydrate status and ethylene sensitivity The carbohydrate status of the unrooted cutting affects the cutting sensitivity to ethylene. Ethylene is produced by cuttings as a result of the wounding procedure and the postharvest environment. If a cutting is relatively healthy, as indicated by the carbohydrate status (sugar and starch concentration), it is relatively insensitive to the ethylene; however, if the cutting carbohydrates are low, then the cutting is much more sensitive to the ethylene and subsequent leaf yellowing and/or abscission will occur. 1-MCP (1-methylcyclopropene) reduced the ethylene sensitivity of cuttings regardless of the cutting carbohydrate status. This work has been conducted on lantana, portulaca, and zonal geraniums.
Ethylene sensitivity.
Unrooted cuttings of 59 taxa representing 28 genera were tested for sensitivity to treatment with 0.1 or 1.0 ppm exogenous ethylene for 24 hours. Cuttings of begonia, lantana, and portulaca showed leaf abscission when treated with ethylene. With all affected species the defoliation due to ethylene was prevented by MCP treatment.
Ethylene produced other effects on alternanthera ‘Party Time’ in that the ethylene treated cuttings were shorter than those not treated with ethylene. Due to the relatively low number of cuttings tested, other species may have been similarly affected by ethylene but symptoms were too subtle to be detected.
Previous work has shown that MCP may slow rooting of hibiscus, chrysanthemum and geranium cuttings. In the current study most species were unaffected by MCP. However, the rooting of angelonia ‘Lavender Carita’, begonia ‘Miss Murry’, and begonia ‘Snowcap’ cuttings may have been reduced by MCP. The rooting of geranium ‘Rocky Mountain White’ was reduced by ethylene exposure and that of fuchsia ‘Honeysuckle’ was increased by ethylene. In all of these instances, however, the actual change in rooting was slight and should be investigated further.
MCP treatment effects on root development. Significant differences in root length were observed between MCP-treated and control zonal geranium cuttings. Root area also was reduced by MCP treatment. MCP-treated cuttings grew roots that were shorter and thicker than untreated cuttings. Leaf yellowing during rooting was reduced by the use of MCP; however, number of leaves abscised was greater.
There are clear effects of MCP on the quality of subsequent root development in zonal geranium. Though MCP cuttings are less likely to develop yellow leaves, the reduced root development may offset this advantage. Further experimental replication, data collection of ethylene response, and dry weight will likely help clarify the MCP response. The next step is to find an MCP dosage that delays senescence, while minimally impacting root development.
Modified atmosphere storage of cuttings. Unrooted zonal geranium and New Guinea impatiens cuttings were harvested, placed in glass jars, flooded for 10 minutes with nitrogen, then with varying combinations of O2 and CO2, sealed and placed at 20 °C for 8 days in the dark. The following combinations of O2/CO2 (%) were used: 21/0, 10/10, 10/5, 10/0, 5/10, 5/5, 5/0, 1/20, 1/10, 1/5, 1/0. Some treatments, generally those with 5% oxygen, produced results similar to what has been seen on some shipments of commercial cuttings - mushy, brown and water-soaked within 24 to 48 hours. However, cuttings treated with 1% oxygen were held for a full eight days with successful subsequent rooting.
Current experiments have identified modified atmosphere conditions that may prove useful in storage and shipping of unrooted cuttings. The 1% O2/20% CO2 treatment also appears to slow respiration in both zonal geranium and New Guinea impatiens. Further replications of these experiments will substantiate the significance of these early results.
Summary and Promotion of Work.
Our work has determined the optimal storage temperatures and durations for dahlia, diascia, geranium, double impatiens, New Guinea impatiens, lantana, lavender, perilla, poinsettia, and portulaca unrooted cuttings. Respiration rates during storage, an indicator of propagation success after storage, were determined for double impatiens, New Guinea impatiens, petunia, and poinsettia cuttings. Ethylene production rates have also been determined for lantana, poinsettia, and portulaca unrooted cuttings as ethylene can damage cuttings during storage. We have determined that the carbohydrate status of the unrooted cutting affects the cutting sensitivity to ethylene. Storing zonal geranium and New Guinea impatiens cuttings with a 1% O2/20% CO2 atmosphere appeared to slow respiration in both species.
Of 59 taxa, representing 28 genera, cuttings of begonia, lantana, and portulaca showed leaf abscission when treated with 0.1 or 1.0 ppm ethylene. Effects of ethylene could be prevented with MCP treatment. However, MCP may be negatively affecting rooting.
Results were disseminated to cutting producers at the 2005 International Plug and Cutting Conference in Dearborn last year. In addition, presentations will be made at the OFA Shortcourse in July.
