A potential alternative to fungicides using actives-free (meth)acrylate polymers for protection of wheat crops from fungal attachment and infection

Abstract

Fungicidal compounds are actives widely used for crop protection from fungal infection, but they can also kill beneficial organisms, enter the food chain and promote resistant pathogen strains from overuse. Here we report the first field crop trial of homopolymer materials that prevent fungal attachment, showing successful crop protection via an actives-free approach. In the trial, formulations containing two candidate polymers were applied to young wheat plants that were subject to natural infection with the wheat pathogen Zymoseptoria tritici. A formulation containing one of the candidate polymers, poly(di(ethylene glycol) ethyl ether acrylate) (abbreviated DEGEEA), produced a significant reduction (26%) in infection of the crop by Z. tritici, delivering protection against fungal infection that compared favourably with three different commercially established fungicide programmes tested in parallel. Furthermore, the sprayed polymers did not negatively affect wheat growth. The two lead polymer candidates were initially identified by bio-performance testing using in vitro microplate- and leaf-based assays and were taken forward successfully into a programme to optimize and scale-up their synthesis and compound them into a spray formulation. Therefore, the positive field trial outcome has also established the validity of the smaller-scale, laboratory-based bioassay data and scale-up methodologies used. Because fungal attachment to plant surfaces is a first step in many crop infections, this non-eluting polymer: (i) now offers significant potential to deliver protection against fungal attack, while (ii) addressing the fourth and aligning with the eleventh principles of green chemistry by using chemical products designed to preserve efficacy of function while reducing toxicity. A future focus should be to develop the material properties for this and other applications including other fungal pathogens.

Fig. 1. Certain homopolymers of interest reduce attachment of a diverse panel of filamentous fungi. Fungal attachment (according to XTT-reduction activity following removal of non-adhering spores) to photo-polymerised (A) or thermal polymerised (B) homopolymers, relative to uncoated polystyrene control (grey). An arbitrary threshold of 25% attachment relative to control is signified by the red dotted line. Fungi were tested in technical (n = 3) and biological (n = 3) replicates, with error bars denoting standard error of the mean (SETM) between biological replicate values.

Fig. 2. Absence of toxic effects of the homopolymers on fungal growth. Fungal growth after 14 days in PDB medium in wells coated with the different polymers, relative to control growth in uncoated wells. Fungi were tested in technical (n = 3) and biological (n = 3) replicates, with error bars denoting standard error of the mean (SETM) between biological replicate values. *p < 0.05 and ****p < 0.0001 according to the Kruskall–Wallace test.

Fig. 3. Wheat infection by Z. tritici in polymer- or fungicide-treated plants. (A) Representative images of wheat plants at 10 weeks after first treatment. From left to right: Untreated, and mMAOES-, DEGEEA-, or fungicide programme 3-treated. (B) Percentage leaf-area infected (left panel) and green leaf areas (GLA; right) in leaves 3 and 4, measured 8 weeks post-application of first treatments. (% infected and GLA values do not necessarily add up to 100% due to effects of other factors, such as leaf senescence with aging or insect damage). Wheat leaves were either untreated (control) or sprayed using treatments indicated in the mini-legend (as detailed in Table 1). (C) The same parameters as in (B) for leaves 1 and 2 measured after 10 weeks. (D) Wheat plant height measured 13 weeks after first treatments, as indicator of potential phytotoxicity. *p < 0.05; ***p < 0.001; ****p < 0.0001, according to the Kruskall–Wallace test. Mean values are shown ± SETM.