Estimation of film antitranspirant spray coverage on rapeseed (Brassica napus L.) leaves using titanium dioxide

Abstract

Film antitranspirant (AT) forms a physical layer to block stomata on the leaf surface and thus improve plant water status under drought. There is little understanding of how leaf coverage relates to the physiological mechanism, so a reliable method of evaluating AT spray deposition is needed. Titanium dioxide (TiO2) is widely applied to heighten the whiteness, brightness and opacity of materials, which can be potentially used as an inert marker to visualize AT deposited on leaves. This study aimed to evaluate the effect of TiO2 on the spray characteristics and coverage of film AT (a.i. di-1-p-menthene) on water-sensitive papers (WSP) and its subsequent use to explore the dose-response relationship between this AT and leaf coverage. Spray characteristics when applied through standard 110° flat fan nozzles were assessed using a droplet analyzer and coverage was measured using image analysis of deposition on water sensitive paper (WSP) and oilseed rape leaves. There was no significant difference observed with TiO2 added to film AT and water in droplet size spectra. Spray coverage averaged 46.8% and 57.3% respectively when WSP were positioned at 70 cm and 50 cm below nozzles. Adding TiO2 to AT solutions with different dose rates had no significant effects on WSP spray coverage at either nozzle height. Leaf coverage was positively correlated with the dose rates of AT at the distance of 50 cm from nozzles to the canopy. Overall, results suggest that TiO2 did not affect droplet size spectra or deposition on WSP of the AT when applied through a flat fan nozzle. Therefore, TiO2 can be effective as a tool to estimate the leaf coverage of film AT on rapeseed for use in future physiological studies.