*4.1. Reagents*

Stevioside standard was purchased from Wako (Osaka, Japan). Gallic acid, silymarin, ferulic acid, curcumin, choline chloride, urea, glycerol, and silver nanoparticles (40 nm particle size (TEM), 0.02 mg·mL−<sup>1</sup> in aqueous buffer, with sodium citrate as a stabilizer) were purchased from Sigma-Aldrich/Merck KGaA (Darmstadt, Germany).

Chitosan oligomers were obtained from medium molecular weight chitosan (supplied by Hangzhou Simit Chemical Technology Co., Ltd., Hangzhou, China), dissolving 10 g in 500 mL of acetic acid (1%) under constant stirring at 60 ◦C. Once dissolved, hydrogen peroxide (0.3 mol·L−1) was added for the degradation of the polymer chains, obtaining oligomers of less than 2000 Da [60].

Liquefaction of the choline chloride and urea (1:2 *v/v*) eutectic mixture occurred at 80 ◦C under stirring in a hot-plate magnetic stirrer for 10 min, in good agreemen<sup>t</sup> with Biswas et al. [61].

#### *4.2. Microwave-Assisted Preparation of the Polyphenol Inclusion Compounds*

The aqueous biphasic system separation technique was used for the formation of the inclusion compounds. This technology is a liquid-liquid extraction system for bioseparation and is frequently used to process all types of biotechnological materials, such as proteins, enzymes, phytochemicals, nucleic acids and pigments [62]. In the case under study, the inclusion complexes formed with stevioside were recovered from the upper part of the reactor.

#### *4.3. Chitosan Oligomers (COS)-Based Composites*

In each of the four jars with screw caps, 1 g of chitosan oligomers of 2000 Da (COS), 0.06 g of stevioside and 0.01 g of one of the polyphenols (either gallic acid, silymarin, ferulic acid or curcumin) were added to 40 mL of hydroalcoholic solution (1:1 *v/v* distilled water and ethanol), followed by treatment in a microwave (Milestone Ethos-One, Sorisole, BG, Italy) at 80 ◦C for 20 min under stirring. The resulting solutions were centrifuged at 2500 rpm and stored at 4 ◦C. For the incorporation of the silver nanoparticles to the nanocomposite, 0.1 mL of commercial AgNPs (0.02 mg·mL−1) were added dropwise to 0.9 mL of the previously centrifuged microwave fractions, and the final solution (with pH 7.5) was stirred at room temperature.

#### *4.4. Deep Eutectic Solvent-Based Composites*

To prepare the DES-based composites, 20 mL of choline chloride and urea (1:2 *v/v*) DES and 10 mL of glycerol were added to each of the four jars with screw caps, together with 0.03 g of stevioside and 0.01 g of the respective polyphenol (gallic acid, silymarin, ferulic acid or curcumin). The mixture was heated at 80 ◦C in the microwave, under stirring, for 20 min. Then, 0.1 mL of AgNPs (0.02 mg·mL−1) were added dropwise to 0.9 mL of the microwave fractions (previously centrifuged at 2500 rpm). The mixture, with pH 7.5, was subjected to vigorous stirring for 5 min at room temperature.

#### *4.5. Silver Nanoparticles-Only Treatments*

Two additional treatments consisting of 0.1 mL of AgNPs (0.02 mg·mL−1) added dropwise to 0.9 mL of the dispersion medium (either COS or DES), without the polyphenol inclusion compounds, were prepared for control purposes. The mixtures were vigorously stirred for 5 min at room temperature.

#### *4.6. Characterization of the Nanocomposites*

The structure and properties of the nanocomposites obtained through the synthetic procedures described above were characterized using Fourier-Transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results were recently reported in patent P201731489 [36].

#### *4.7. Fungal Isolates and Growth Conditions*

The fungal species used in the experiment was *Phytophthora cinnamomi* isolate MYC43, supplied by Centro de Investigaciones Científicas y Tecnológicas de Extremadura—Instituto del Corcho, la Madera

y el Carbón Vegetal, Spain. The isolate was maintained in potato-dextrose-agar (PDA) slant tubes, supplied by Merck Millipore (Darmstadt, Germany), stored at 4 ◦C.

#### *4.8. Efficacy of the Nanocomposites for the Control of Phytophthora cinnamomi*

Agar disks (8 mm in diameter) were cut from the margin of a 7-day-old colony growing on PDA and were transferred to a PDA medium supplemented with the nanocomposites at final concentrations of 125 <sup>μ</sup>g·mL−1, 250 <sup>μ</sup>g·mL−<sup>1</sup> and 500 <sup>μ</sup>g·mL−1. Three replicates were performed for each treatment. For each active ingredient and concentration, inhibition of radial mycelial growth (mm) compared with the untreated control was evaluated after 7 days of incubation at 24 ◦C, in the dark. The relative growth inhibition (%) of each treatment compared to untreated control was calculated as follows: Growth inhibition (%) = [(*dc* − *dt*)/*dc*] × 100, where *dc* stands for the average diameter of the fungal colony in the control and *dt* is the average diameter of the treated colony [63]. Results were expressed as effective concentrations EC50 and EC90 (i.e., the concentrations which reduced growth inhibition by 50% and 90%) by regressing the inhibition of radial mycelial growth values (% control) against the values of the antifungal nanocomposite concentrations.
