Nanoscale Nutrients Protect Plants from Fungal Infection

Chances are, most — if not all — of the produce in your kitchen is threatened by fungal diseases. The threat looms large for food staples of the world such as rice, wheat, potatoes, and maize. Pathogenic fungi are also coming for our coffee, sugarcane, bananas and other economically important crops. Annually, fungal diseases destroy a third of all harvests and pose a dire threat to global food security.

To stop the spread of fungal diseases, farmers fumigate the soil with toxic chemicals that lay waste to the land, sparing not even the beneficial microbes teeming in the earth. Or they ply plants with fungicides. But fungicide use is effective only in the short run — until the pathogenic fungi evolve resistance against these synthetic chemicals.

Now, a new idea is taking root: Help plants stand their ground by giving them the tools to fight their own battles. A science team is fortifying crops with nutrients fashioned into nanosized packages, which boost plants’ innate immunity against pathogenic fungi more efficiently than traditional plant feeding. Over the past few years, the researchers have devised various nano nutrient concoctions that boost the fungal resistance of soybeans, tomatoes, watermelons and, recently, eggplants. The scientist's strategy provides plants with the nutrients they need to trigger enzyme production to guard against pathogenic attacks. Without any synthetic chemicals introduced, the strategy sidesteps an opportunity for malignant fungi to develop resistance.

The researchers’ nanomaterials approach is inspired by their earlier discovery that nanoparticles transported up from the roots of maize can loop back down from the leaves. The researchers dipped half of the root fibers of a single maize plant in a copper nanoparticle formulation and the other half in pure water. The copper showed up in the water-dipped roots, pointing to a roots-to-shoot-to-roots roundtrip. That finding suggested that nanoparticles can be applied directly to the leaves in the first place, even when the target destination was the roots.

Using the leaves as an entrance point gets around a perennial problem: Delivering dissolved nutrients through the soil is hardly efficient. Chemicals may break down in the soil, vaporize into the atmosphere or leach away. Only about 20 percent of watered nutrients eventually reach the target areas in a plant. To see if this approach could deliver nutrients specifically needed in defense against hostile fungi, scientists carried out tests in eggplants and tomatoes. The team sprayed metallic nanoparticles onto the leaves and shoots of young plants, then infected the plants with pathogenic fungi. The nanoparticle-treated plants had elevated levels of nutritional metals in the roots and higher produce yields compared with the plants fed 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.

W.H. Elmer et al. Influence of single and combined mixtures of metal oxide nanoparticles on eggplant growth, yield, and verticillium wilt severity. Plant Disease. Vol. 105, April 2021, p. 1153. doi: 10.1094/PDIS-07-20-1636-RE.

Y. Shen et al. Copper nanomaterial morphology and composition control foliar transfer through the cuticle and mediate resistance to root fungal disease in tomato (Solanum lycopersicum). Agricultural and Food Chemistry. Vol. 68, October 14, 2020, p. 11327. doi: 10.1021/acs.jafc.0c04546.