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- Author or Editor: David A. Francko x
Freezing temperatures present major constraints for palm cultivation in temperate regions. As a result of their landscape value, there is a constant need for appropriate species and cultivars for freeze-prone areas. The objective of the present study was to evaluate the suitability of the chlorophyll fluorescence technique for quantitative assessment of freezing injury in palms. Five palm species known to differ in their freezing tolerance were selected: Copernicia alba, Washingtonia filifera, Sabal palmetto, Trachycarpus fortunei, and Rhapidophyllum hystrix. Leaf segments were frozen at –5, –10, –15, and –20 °C for 1 h. Repeated freezing–thawing cycles were additionally performed in young and older leaves of R. hystrix. Depending on the species and temperature, significant differences in the ratio of variable-to-maximal fluorescence (Fv/Fm) were detected 3 h after the freezing treatment, whereas visual symptoms appeared after 24 h. A strong positive correlation (r 2 = 0.94) was found between the injury index calculated from Fv/Fm values and the index of injury based on the electrolyte leakage technique. Although both indices provided similar information, the nondestructive chlorophyll fluorescence method allows monitoring the progression of damage as well as the eventual recovery taking place in the leaf tissue after freezing.
A novel topical spray was developed to increase resistance to both cold damage and cold mortality in plant foliage, flowers, and fruits. In environmental chamber experiments, application of the spray to monocot and dicot foliage lowered the environmental temperatures associated with the first onset of cold injury and with cold mortality from 2.2 to 9.4 °F, compared with controls sprayed with tap water, over an effective temperature range (depending on species) of ≈0 to 32 °F. The threshold temperature for flower mortality was lowered from 2.2 to 3.2 °F depending on species. Mature fruit suffered significantly less freeze damage when pretreated with the spray formulation. The spray is composed of ingredients that are non-toxic to plants, humans, and other animals. The patent-pending formulation has been commercialized under the trade name FreezePruf.