By Muhammad Shahid
Winter freeze is the main threat to the emerging citrus industry in North Florida, South Georgia and Southeast Alabama. Growers use microsprinkler irrigation as a freeze-protection strategy to protect the graft union of young trees, but it is not very effective in protecting aboveground plant parts in established trees.
Use of stress-mitigating substances could be an effective approach to improve a plant’s tolerance to freezing. Potassium (K+) can enhance the plant’s ability to cope with stress. High concentrations of K+ lower the freezing point of the plant’s cell solutions. Furthermore, adapted cytosol K+ concentration is essential for enzyme activities that are involved in frost resistance.
Silicon (Si) is also an important micronutrient that can protect plants from freeze damage by modification of the cell wall and prevention of membrane damage. In addition, Si can enhance the stability of cuticles on the leaves and help plants protect against heat and cold stress.
University of Florida Institute of Food and Agricultural Sciences researchers have examined the role of exogenous applications of Si (50 ppm + 100 ppm) and K+ (50 ppm + 100 ppm) on Owari satsuma under different freezing temperatures from 32 degrees to 14 degrees Fahrenheit in a programmed freezing chamber and on farm trials under field conditions. Overall, the Si alone and in combination with K+ enhanced the freezing tolerance.
Field trials are ongoing to determine the best Si application rate and application frequency for getting the optimum cold hardiness in satsuma mandarin and red navel orange.
- Silicon alone or in combination with potassium is effective in improving the cold hardiness in satsuma mandarin and red navel orange.
- Silicon at 150 ppm is the safe level for use in citrus production systems, but more research is needed to refine the application rate for different species.
- Silicon is an ecofriendly and economical substance to add in the citrus nutrition program.
Muhammad Shahid is an assistant professor at the UF/IFAS North Florida Research and Education Center in Quincy.