Novel approaches for visualising and characterising micro roughness of surfactant treated leaf surfaces

Vittal LVM1, Jones PW3, Killick AR3, Boyd BJ2 and Cahill DM1

  1. Schools of Life and Environmental Sciences, Deakin University, Geelong Waurn Ponds Campus, Victoria, Australia,.
  2. Drug Delivery Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University Parkville Campus, Victoria, Australia.
  3. Victorian Chemical Company, Coolaroo, Victoria, Australia.

Surfactants are agrochemical additives that enable penetration of active ingredients into foliar surfaces. Surfactants interact with epicuticular waxes (EW) on foliar surfaces and cause structural change which can compromise surface integrity. Surface structural changes are usually visualized using electron microscopy (EM) and are recorded by visually inspecting and allotting a ’phytotoxicity’ score, subject to confirmation bias. The purpose of this study was to characterize changes in EW post treatment with four commercial surfactants on the leaf surfaces of canola (Brassica sp.), wild radish (Raphanus sp.), wheat (Triticum sp.) and wild oats (Avena sp.). Two different methods were used to analyse the leaf surfaces: 1) Treated/ untreated surfaces were imaged using EM and their lacunarity (fractal dimension) was calculated using FracLac, a 2D approach and, 2) surfaces were profiled using an optical profilometer, a 3D approach. Changes in the wax morphology was clearly observed using both techniques. Leaves treated with a high concentration of surfactant showed higher lacunarity. Change in profile roughness was measured for a section, Ra, as well as for the whole area of the profile. Sa. The optical profiler also doubled as a microscope allowing visualization of waxes in their native state without any sample preparation steps. We propose that these two techniques when used in tandem are reliable methods to physically evaluate surfactant phytotoxicity on leaf surfaces. The methods will also find use more broadly for plant surface analysis.