*2.1. Accelerated Photo-Degradation*

Assessment of resistance to accelerated photo-degradation included four treatments groups each with six replicates. These included the MBCC treatment, with and without peroxide post-treatment, the iron oxide-based colorant as a reference product, and untreated red pine sapwood as a control. Specimen size was 75 mm long × 75 mm tangential × 12 mm radial wood fiber direction.

The sample color was evaluated with a SP60 spectrophotometer (X-Rite, Grand Rapids, MI, USA) using CIE *L*\**a*\**b* color space. *L*\* represents lightness on a scale from 0 to 100. Negative *a*\* values indicate degree of greenness, while positive values indicate degree of redness. Negative *b*\* values indicate degree of blueness, while positive values indicate degree of yellowness. CIE *L*\**a*\**b*\* data were used to calculate Δ*L*\* (change in lightness), Δ*a*\* (change in green-red color), Δ*b*\* (change in blue-yellow color), and Δ*E*\* which represents the total color change according to Equation (1).

$$
\Delta E^\* = \sqrt{(L\_2^\* - L\_1^\*)^2 + (a\_2^\* - a\_1^\*)^2 + (b\_2^\* - b\_1^\*)^2} \tag{1}
$$

A small amount of vinyl polysiloxane (Aquasil Ultra Smart Wetting®, Dentsply Caulk, Montreal, QC, Canada), approximately 10 mm × 20 mm, was stuck to three samples from each treatment group. This was used to provide an unexposed reference patch from which to measure erosion following Q Sun exposure. After Q-Sun exposure, the silicone was removed from the surface. A 3D profilometer, Contour GT-K1, (Veeco Instruments, Plainview, NY, USA) was used to measure the erosion of the exposed area compared to the unexposed sections. A total of six measurements were taken per sample (three samples/series of treatment) for a total of eighteen replicates per series of treatment.

Samples were placed in a Q-Sun chamber (Q-Lab Corporation, Westlake, OH, USA) for accelerated photo-degradation. The samples were exposed using the ASTM G-155 cycle 1 method [16]. This cycle includes 102 min of exposure to light at 0.35 <sup>W</sup>/m<sup>2</sup> irradiance at 340 nm and 63 ◦C for black panels. The chamber air was maintained at 43 ◦C and 30% relative humidity. This was followed by 18 min of exposure towater andlight at 0.35W/m<sup>2</sup> irradiance at 340 nm and 63 ◦C for black panel. Colormeasurements were repeated after 1000 h of exposure.

#### *2.2. Black-Stain Fungal Resistance*

After inspection at 1000 h of exposure, samples from the accelerated photo-degradation experiment were exposed to an additional 500 h of exposure in the Q-Sun. These samples (exposed for a total of 1500 h in the Q-Sun chamber) were cut into four 35 mm × 35 mm × 12 mm subsamples. In addition, red pine sapwood that had not been exposed in the Q-Sun was included as control, and red pine sapwood pressure impregnated with a solution of 1% propiconazole, and 0.5% 3-iodo-2-propynyl butyl carbamate (IPBC) was included as an additional reference known to control black-stain fungi [17]. Twenty-four replicates (6 replicates of each treatment × 4 subsamples) were produced for each treatment. Group A included two isolates with typical *Aureobasidium pullulans* morphology that were isolated from coated wood in Vancouver, BC, Canada. Group B included two isolates with darker and more yeast-like colony morphology that were slower growing on nutrient plates than group A and were isolated from coated wood in eastern Canada. Group C, isolated from both western and eastern Canada, included a mix of ten isolates of various colony types collected from coated wood affected by black stain after only 2 years of in service exposure. Group D was sprayed with distilled water and used as an uninoculated reference. All subsamples were edge sealed with a marine epoxy (Intergard 740, International Marine Coatings, Singapore) and sterilized by ion beam irradiation with two passes at 17 kGy (Iotron Industries, Port Coquitlam, BC, Canada). Prior to inoculation, the samples were aseptically placed in test chambers with 2 mL of sterile distilled water and left to incubate at 22.5 ◦C for 48 h to ensure a moist surface for inoculation. Test chambers are described in [17].

To prepare a spore suspension for inoculum groups A and B, a solution of distilled water with Tween® 20 (Sigma-Aldrich, Oakville, ON, Canada), a polysorbate-based non-ionic surfactant, was used to gently remove spores from the surface of two actively growing plates by gently shaving the sporulating mycelium using a sterile scalple of each chosen isolate and making up to a final volume of 200 mL. For inoculum C, the solution of sterile water with Tween® 20 was again used to remove spores from the surface of one actively growing plate of each of the ten chosen isolates and the final volume made to 400 mL. The solutions were blended with three short pulses in a Waring commercial blender. The inoculum was then filtered through a prewashed sterile glass wool-lined glass funnel to remove large particles that could plug the air brush. Haemocytometer average counts of spore suspensions for inoculum A, B and C were 1.1 × 106, 0.54 × 10<sup>6</sup> and 2.2 × 10<sup>6</sup> spores per millilitre of the 200 and 400 mL spore suspensions, respectively. The inoculum was applied using an IWATA Eclipse (Anest Iwata-Medea, Inc., Portland, OR, USA) HP-BCS airbrush, 5 mL of inoculum was used to evenly coat twelve test pieces at a time. Inoculum sprayed on control plates (1% malt extract agar) developed a healthy growth of black-stain fungi for each inoculum group after a few days of incubation, while plates sprayed with just water inoculum had no growth. Test samples were incubated at 22.5 ◦C in the dark for six weeks. A weekly in situ spritzing with sterile distilled water was applied by a gentle spray over the sample surface to maintain a suitable moisture content.

Samples were inspected after two, four and six weeks of incubation based on the visual inspection scale described in [18]. However, it was noticed that some fungi altered the color of the surface but had no visible growing mycelia or sporing structures on the surface. For such samples, the discoloration observed on the surface was compared to uninoculated control samples, and a rating was given based on the amount of discoloration present and not only on visible fungal growth on the surface. Ratings of 0 indicated no stain, while ratings of 5 indicated intense and widespread staining of the sample.
