Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 3, 2001
Publication Date: February 11, 2002
Interpretive Summary: In the United States, frost damage is common in many states every year, and sometimes occurs repeatedly. The consequence of these frost episodes can be very costly and losses have been estimated to be over two billion dollars in Florida alone in 1983. Existing methods of frost protection are ineffective, too costly, or environmentally unfriendly. Therefore, a key mission for USDA-ARS is to develop a better understanding of freezing in plants in order to develop new methods of frost protection. In the present study, we examined the ability of hydrophobic (water-repelling) particle films to provide a barrier on the outside of the plant preventing external ice crystals from growing into the plant and inducing it to freeze. We used an infrared video camera to monitor the freezing process in a non- intrusive manner. Our results indicate that some species of plants, such as tomato, can have the temperature of their tissues be several degrees below 32 F without freezing. Thus they remain uninjured. It is only when ice crystals present on the leaf surface can penetrate into the plant tissue that the freezing of the plant occurs. The hydrophobic particle film was able to prevent, for a significant period of time, these external ice crystals (which form during natural frost episodes) to induce the tomato plants to freeze. The use of hydrophobic particle film represents a new method of frost protection and has been patented by the USDA-ARS. Further field research will be conducted in order to determine the potential of this technology as a practical and economical method of frost protection.
Technical Abstract: In herbaceous plants, extrinsic ice nucleating agents significantly limit the ability to supercool below 0 C. We have used infrared video thermography to study freezing in young tomato (Lycopersicon esculentum, 'Rutgers') plants and to determine if a hydrophobic barrier on the plant surface could prevent the action of extrinsic nucleating agents from initiating freezing within a plant. Tomato plants were grown in a greenhouse in individual pots and used when they were 4-6 weeks old. Freezing tests were conducted in a programmable freezing chamber, a radiative frost chamber, and outdoors. Freezing of the plants was extrinsically induced by the application of droplets of water containing Pseudomonas syringae (strain Cit7). To provide a barrier to the action of extrinsic ice nucleating agents, an emulsion of hydrophobic kaolin was applied to the plant surface prior to application of an extrinsic nucleating agent. Results show that dry, young tomato plants can supercoo to as low as -6 C whereas plants having a single droplet of Cit7 freeze at -1.5 to -2.5 C. Application of the hydrophobic barrier blocked the effect of Cit7 and allowed whole plants to supercool to -6C. When whole plants were sprayed with water and Cit7 using an aerosol sprayer and exposed to -3C, plants coated with the hydrophobic particle film exhibited a significant increase in survivability over untreated plants. Similar results were obtained using the radiative frost chamber. Experiments in natural frost conditions also resulted in less injury in the coated plants. The hydrophobic kaolin particle film performed better preventing plants from freezing due to extrinsic ice nucleation than unaltered kaolin alone or anti-transpirants with putative frost protection properties.