Inspired by peaches, chemists are developing a new coating method to protect seeds from hungry insects.
Peach pits, which are hidden inside the nut-like husk, contain amygdalin, a substance that can degrade into hydrogen cyanide in the stomach. Peaches, as well as apricots and bitter almonds, use this defense system to protect the seeds from insects.
Chemists from Wendelin Stark’s research group at ETH Zurich are developing a coating for seeds that functions in the same way as this natural model and is just as effective, but doesn’t impair seed germination and is also biodegradable. They report their work in the Journal of Agricultural and Food Chemistry.
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To determine the efficacy of a coating, the researchers tested different layer sequences. The most effective sequence consists of several layers of polylactic acid (PLA), a substance that is harmless to both humans and the environment. The innermost layer contains an enzyme. On top of this lies a layer of pure polylactic acid, followed by two layers embedded with the hydrogen cyanide precursor amygdalin—the same substance found in the husks of bitter almond seeds. A final layer is composed of pure PLA.
If an insect larva chews through these layers, the amygdalin is released, followed by the enzyme. The two substances mix together and the amygdalin breaks down into hydrogen cyanide, which kills the insect larva’s appetite—or just plain kills it.
The researchers have tested the efficacy of their treatment on a variety of cereal pests. The bitter almond defense system proved very effective against the larvae of the mealworm (Tenebrio molitor), the Indian mealmoth (Plodia interpunctella), and the lesser grain borer (Rhizopertha dominica). The lesser grain borer is a beetle that causes considerable damage to wheat stores worldwide.
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Significantly fewer full-grown beetles hatched on coated than uncoated seeds. They reproduced less successfully and the larvae grew more slowly because they had eaten less.
However, the layering didn’t keep all insects from feasting on the wheat grains: the treatment was not effective against the wheat weevil (Sitophilus granarius). This type of beetle does not lay its eggs on the grain, but instead bores a hole into it for the eggs and seals it up afterwards. The larvae then eat the wheat grain from the inside out, which means that they don’t come into contact with the coating.
The researchers were able to show in laboratory and fieldwork that the treatment did not impair the germination of wheat grains. In the lab, 98 percent of the coated grains germinated. In the field, the coated grains did germinate a little later than the uncoated ones, and the seedlings developed more slowly at first. Nonetheless, the wheat plants were able to recover this initial deficit later on.
The treatment using this method is as straightforward as spraying. The new method isn’t significantly more expensive than insecticides.
The researchers are convinced that this kind of seed coating can be used on other kinds of crops too. “The method has the potential to replace certain synthetic pesticides,” says researcher Carlos Mora. “Not only is the coating biodegradable, but it also ensures that the seeds retain their quality in storage.”
Source: ETH Zurich