Most, if not all, of the produce in your kitchen is likely to be infected with fungal illnesses. The threat looms huge for global food mainstays such as rice, wheat, potatoes, and maize. Pathogenic fungus are also targeting our coffee, sugarcane, bananas, and other commercially significant crops. Fungal diseases destroy one-third of all harvests each year, posing a serious danger to world food security.
Farmers fumigate the soil with deadly chemicals to stem the spread of fungal diseases, destroying the land and killing even the helpful bacteria that live there. Or they spray fungicides on the plants. However, fungicides are only effective in the short term, until pathogenic fungus develop resistance to these synthetic agents.
Now, a new notion is taking root: Help plants defend themselves by arming them with the tools they need to fight their own conflicts. A team led by environmental toxicologist Jason White of the Connecticut Agricultural Experiment Station in New Haven is supplementing crops with nutrients fashioned into nanosized packets, which strengthen plants’ innate protection against pathogenic fungus more effectively than traditional plant feeding. As published in the April Plant Disease, the researchers have developed numerous nanonutrient concoctions that improve the fungal resistance of soybeans, tomatoes, watermelons, and, most recently, eggplants.
The method “addresses the dilemma at its source rather than attempting to bandage the [problem],” according to Leanne Gilbertson, an environmental engineer at the University of Pittsburgh who was not involved in the research. White’s technique gives plants with the nutrients they require to stimulate enzyme production, which protects them from pathogenic attack. She claims that because no synthetic chemicals are used, the technique eliminates the possibility of malignant fungi developing resistance.
Chemicals can degrade in the soil, evaporate in the atmosphere, or leak away. Only approximately 20% of watered nutrients make it to the target parts of a plant. We can actually more efficiently deliver [nutrients] where we want it and where the plant needs it by employing the nanoscale form.
Jason White
The researchers’ nanomaterials technique is motivated by their previous discovery that nanoparticles sent up from maize roots can loop back down from the leaves. The researchers immersed half of a single maize plant’s root fibers in a copper nanoparticle mixture and the other half in clean water. The copper was found in the water-dipped roots, indicating a roundtrip from roots to shoots to roots, according to a study published in Environmental Science & Technology in 2012. This finding revealed that nanoparticles might be given directly to the leaves in the first place, even if the roots were the intended destination.
Using the leaves as an entry point avoids a long-standing issue: delivering dissolved nutrients through the soil is inefficient. Chemicals can degrade in the soil, evaporate in the atmosphere, or leak away. Only approximately 20% of watered nutrients make it to the target parts of a plant. “We can actually more efficiently deliver [nutrients] where we want it and where the plant needs it by employing the nanoscale form,” White explains.
White and colleagues tested eggplants and tomatoes to see if this strategy may give nutrients especially needed in defense against hostile fungus. The researchers sprayed metallic nanoparticles on the leaves and shoots of young plants before infecting them with harmful fungi. The scientists published in Environmental Science: Nano in 2016 that the nanoparticle-treated plants had higher amounts of nutritional metals in the roots and better product yields than the plants provided readily dissolved nutrients.
The nanoparticles weren’t harming the fungi, the researchers found: The fungi still thrived amidst nanoparticles in the environment without the host plant present. Instead, the nanoparticles’ antifungal properties stem from providing plant nourishment — equivalent to humans taking nutritional supplements — that allows plants to mount an appropriate defense on demand.
According to Fabienne Schwab, an environmental chemist who was not involved in the research, what makes nanonutrients more potent than ordinary fertilizers is the sweet spot in their sizes, which determine how quickly they dissolve. Nanonutrients are hundreds of times smaller than human hair and thousands of times larger than easily dissolved nutrient salts. Because they have a vast, exposed surface, they dissolve faster than a larger chunk of the same nutrient. However, nanonutrients are large enough that they do not dissolve all at once: they might release nutrients gradually over weeks. Plants, on the other hand, get a transient nutrient boost from readily dissolved nutrients, similar to a sugar rush.
“When you use [nutrients] at the nanoscale, you can tune the solubility pretty much the way you like,” says Schwab, of the Adolphe Merkle Institute in Fribourg, Switzerland.
It’s not just the size that can be tweaked; the shape, composition, and surface chemistries may all be altered to stimulate different levels of a plant’s reactions. For example, White and his colleagues discovered that nanometer-thin copper oxide sheets outperformed spherical copper nanoparticles in preventing Fusarium virguliforme infection in soybeans. The key to their success was the nanosheets’ faster release of charged copper atoms and greater adherence to leaf surfaces. The copper nanoparticles restored the soybean’s masses and photosynthetic rates to those of disease-free plants, the scientists reported in Nature Nanotechnology in 2020.
“It’s a highly promising technology,” says Schwab, adding that there are other factors to consider before implementing it. If agricultural nanotechnology is to become widely used, it must comply with environmental and safety standards, as well as overcoming consumer skepticism, which may be even more difficult. So far, White and his colleagues have discovered no leftover nanonutrients in their produce that would end up on consumers’ plates. However, other ramifications, such as the persistence of nanomaterials in the environment and the dangers they represent to human handlers, have yet to be completely appreciated.
“When you talk about nanotechnology and food, people get worried,” White adds. However, he claims that his organization is not using any exotic ingredients, the health effects of which are unknown. Instead, “we’re employing nutrients that plants require but can’t get enough of.”
White claims to have consumed the eggplants, tomatoes, and watermelons he grew for his studies. Perhaps the best comfort customers can get is from a toxicologist attempting the real fruit of his effort.
