Biomimetic surfaces can prevent fungal diseases

Researchers at the University of Adelaide, Australia, propose treating foliar fungal diseases as a biointerface problem. The approach seeks to identify the physical and chemical signals used by pathogens to recognize the leaf surface. This knowledge can guide preventative strategies based on genetic improvement and products capable of modifying the properties of the plant cuticle (doi 10.1116/6.0005533).

The concept stems from a step common to foliar pathogens. Before infection, the fungus needs to come into contact with the leaf and recognize the host. Surface characteristics can stimulate spore germination and the advancement of colonization. Interruption of this recognition can prevent or reduce disease development.

First interface

The cuticle covers the aerial parts of plants and forms the first interface with the environment. This layer comprises a matrix of cutin and cuticular waxes. The epicuticular waxes occupy the outer region and define properties such as chemical composition, hydrophobicity, roughness, and topography.

The composition varies between species, cultivars, tissues, developmental stages, and environmental conditions. Waxes include long-chain aliphatic compounds, as well as terpenes, polyphenols, and volatile substances. On the surface, these materials can form crystalline structures with plate-, fiber-, or tubular-like morphologies.

Host recognition

Evidence gathered in the study indicates a biological function of these waxes in host recognition. Fungal spores can detect specific compounds and adjust steps prior to penetration. Barley powdery mildew, caused by Blumeria graminis subsp. hordei, responds to the aldehyde hexacosanal, with a 26-carbon chain. Wheat powdery mildew, associated with Blumeria graminis subsp. tritici, uses octacosanal, with a 28-carbon chain. These compounds occur in the epicuticular waxes of the respective crops.

Traditional infection models use whole leaves. They allow for the assessment of susceptibility in species and cultivars, but make it difficult to separate the effects of surface chemistry, morphology, physiology, and immune responses, the scientists explain. Natural tissue variation also reduces the reproducibility of the assays.

Many studies evaluate metabolic, proteomic, or transcriptomic changes after disease establishment. These methods describe subsequent responses, but do not isolate the factors responsible for the pathogen's success in its first contact with the plant.

Artificial surfaces

To overcome this limitation, the researchers propose artificial surfaces coated with leaf waxes. The system deposits wax extracts onto inert substrates and forms films with a known composition. The spin coating technique spreads a solution over a moving surface and produces a thin, uniform layer.

The model preserves the chemistry found in the leaf and removes some of the complexity of living tissues. The rotation speed, solvent, volume, and solution concentration allow control of film thickness and hydrophobicity. Tests can relate these properties to spore germination.

Preliminary data

Preliminary data presented by the scientists show germination of two subspecies of Blumeria graminis on surfaces coated with waxes from different plants. The integration between the biological results and the characterization of the films may reveal compounds or properties capable of stimulating the disease.

Early models produce smooth surfaces. They don't reproduce the full natural morphology of waxes, but they allow for the separation of the effect from chemical composition. Future systems may incorporate roughness, topography, chemical gradients, temperature, and humidity. Other deposition and microfabrication techniques may also expand the control over surface characteristics.

The proposal includes the evaluation of different crops and pathogen groups. Much of the available research focuses on biotrophic powdery mildews. The inclusion of rusts, rots, spots, and other agents could support the construction of susceptibility databases. These databases would gather information on the crop, fungus, and surface variable.

Plant selection

The results may guide the selection of plants with wax profiles less favorable to recognition by the pathogen. Breeding and gene editing programs could exploit this diversity. Another alternative involves cuticle-inspired sprays, formulated to modify the leaf surface and confuse the fungi's detection mechanisms.

These strategies still require validation in plants and under field conditions. The goal is to shift management from post-treatment to preventing infectious contact. This approach does not replace fungicides or resistant cultivars, but offers a new line of investigation to reduce the incidence of diseases.