Scientists have created a long-lasting mechanism to deliver vaccines to plants – a biodegradable clay that sticks to plant leaves for a month – that could save vast quantities of food that might otherwise never get harvested. In a world facing many challenges to feed a growing population, this could prove a very important technology.

Plants have their own immune systems, and stimulating them to fight disease can work like vaccines in humans or other animals. Unfortunately, however, there are substantial obstacles to achieving this on a large scale.

Exposure of plants to double-stranded RNA from the pathogen triggers a response that enables the plant to fight off whatever is attacking it. However, “The naked RNA works very well, but it only lasts two to three days,” lead author Dr Neena Mitter of the University of Queensland told IFLScience. Reapplying RNA every few days would be ridiculously expensive in most circumstances, so Mitter went looking for something longer-lasting.

She found it in what she calls BioClay, which can bind the RNA and, when applied to the leaves of a plant, releases its cargo slowly. BioClay, formed from nanoscale particles, eventually breaks down, leaving no harmful residue. In the journal Nature Plants, Mitter reports that it sticks to the leaves for 30 days, even in heavy rain.

Mitter added double-stranded RNA from common plant viruses to the clay and applied it to plants, providing protection for at least 20 days. “Once BioClay is applied, the plant ‘thinks’ it is being attacked by a disease or pest insect and responds by protecting itself from the targeted pest or disease,” she explained in a statement.

So far Mitter has not demonstrated the technique against other plant pathogens, such as fungi or bacteria. However, she told IFLScience that appropriate RNA has been shown to have a similar protective role against each of these, and even certain insects. Mitter described the success with viruses as a “proof of principle” against other plant diseases.

Mitter added that the process of application is quite easy. “Combining the BioClay with the RNA is a fairly simple process... the clay has a positive charge and the RNA is negatively charged so they stick together.” The combination can then be sprayed onto the plant in need of protection.

With plant diseases destroying major portions of the world's food supply, and global warming expanding the range of tropical plant diseases, there is plenty of demand for a solution. Fungicides can leave toxic residues, and other methods of disease control have mixed success. 

Genetic engineering of resistance has to be done on a species by species basis, making it much slower to create than a technique such as Mitter's, which can be easily adapted to different crops.