The natural product chitosan looks promising as an alternative to synthetic fungicides for controlling postharvest diseases in cherries, research in Italy shows.
Dr. Erica Feliziani conducted a study at the Universita Politecnica della Marche in Ancona, Italy, in which she tested several natural compounds for controlling rot in cherries, table grapes, and strawberries. A commercial chitosan formulation controlled brown rot in cherries as effectively as synthetic fungicides did.
The quest for alternatives to traditional fungicides has become all the more urgent in Europe since the European Union issued a directive that made integrated pest management mandatory in all European member countries starting January 2014, Feliziani reported.
The directive states that member countries need to promote the use of products with low risk to human health and the environment for controlling pests. It also states that where there is a risk that the pathogen will develop resistance to a control measure, antiresistance strategies should be used to maintain the effectiveness of the products.
This can include the use of multiple pesticides with different modes of action or the integration of several methods, possibly including nonchemical.
Chitosan is a polysaccharide derived from treating shrimp and other crustacean shells with sodium hydroxide. It has been approved as a Generally Recognized As Safe substance by the U.S. Food and Drug Administration.
A chitosan application has a dual action, as it not only reduces growth of the decay organism, but induces resistance responses in the plant. It forms a semipermeable coating on the fruit surface that delays respiration and reduces transpiration, prolonging the quality of the fruit in storage. It could even prevent contamination by foodborne pathogens from eventually occurring on the fruit, Feliziani believes. Chitosan had no detrimental effect on the appearance of the fruit.
Cherries are susceptible to postharvest decay caused mainly by Monilinia species but also by Botrytis cinerea and occasionally by other pathogens. At present, preharvest treatments with synthetic fungicides are the main means of control.
Compared with synthetic fungicides, natural products (such as inorganic salts, plant extracts, and essential oils) might be less likely to result in fungal resistance, might be cheaper, and might be applied closer to harvest, Feliziani suggests.
Products she tested included chitosan, benzothiadiazole, laminarin, oligosaccharides, calcium with organic acids, soybean lecithin, potassium bicarbonate, potassium sorbate, nettle extract, and fir extract. Working in an experimental orchard in Ancona, she applied products three days before harvest or shortly after harvest.
The most effective treatments for controlling rots were chitosan and potassium bicarbonate, which are both resistance inducers. Potassium bicarbonate reduced decay of cherries when applied at concentrations ranging from 0.4 to 2.6 percent but at higher doses, it had phytotoxic effects on the skin and pedicels of the cherries.
Other products tested also provided some control; further studies are needed to understand their modes of action and find out how best to use them. Some of the compounds are already commercially available.
Chito Plant, which contains 99.9% chitosan, is available in Germany for control of rots in grapes, cherry, and strawberries. Pure chitosan products are available in Iceland and Thailand for use on other fruits.
In the United States, Advanced Growing Systems, Inc., produces Organisan II-YS, containing chitosan and yucca extracts as an adjuvant, and BASF Corporation manufactures its FreshSeal coating for use on a number of fruits and vegetables, but not deciduous tree fruits. •
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