Biological Frost Control Strategies Developed

 

Ice formation on orange leaf (dark area) initatied by bacteria

Frost damage is a persistent limitation to the production of many important crops and costs California agriculture up to one billion dollars annually. Flowers of deciduous fruit and nut trees, vegetables, and subtropical crops are damaged when temperatures drop even slightly below freezing. Existing methods of frost protection, such as overhead sprinklers, heaters, and wind machines, are very expensive to use, limited by water supplies, and relatively ineffective. For many crops, no methods of frost control are currently available or practical.

 

 
Research undertaken at UC Berkeley's College of Natural Resources has shown that frost-sensitive plants are damaged only when ice forms in the plant and not by cold temperatures per se. Furthermore, certain bacteria commonly found on plants trigger ice formation by a process called ice nucleation. In the absence of these bacteria, plants do not freeze until faced with relatively cold temperatures. This research has shown that ice nucleation active bacteria can be prevented from growing on plants by inoculating crops early in their seasonal development. In the field, researchers demonstrated that both the altered bacteria and other, naturally occurring bacteria successfully competed with the ice nucleation active bacteria on the potato plant. This represented the first field use of genetically engineered microbes in the world. Both reduced the freezing temperature of crops from two to six degrees Fahrenheit and reduced plant frost damage during typical frosts of a temperature of about 28 F by an average of about 80 percent.
 

 
A naturally-occurring bacterial strain from a pear tree in Healdsburg, California, was found to have superior ability to control frost damage when sprayed onto crops. This bacterium also controls fire blight, a devastating disease of pear and apple trees. The bacterium has been commercialized as a freeze-dried preparation of live bacteria that can be sprayed onto crops with standard agricultural spray equipment. This product, Blightban A506, can provide considerable control of frost damage and is registered by the US Environmental Protection Agency for use on a wide variety of crop plants, including pear, apple, strawberry, peach, and potato. In the western US and other regions, a large percentage of the acreage of crops, such as pear and apple, is treated with this antagonistic bacterium for both frost and disease control. The use of this biological control agent provides an environmentally-safe and economical means of frost protection, ensuring crop productivity even when cold temperatures strike.
 

Supporting Unit: UC Berkeley College of Natural Resources, Department of Plant and Microbial Biology
 
Steven Lindow
Department of Plant and Microbial Biology
University of California
111 Koshland Hall
Berkeley, CA 94720-3102
Phone: 510-642-4174
Fax: 510-642-4995
icelab@socrates.berkeley.edu