Effects of Vapor Gard (Di-1-p-menthene) on Potato (Solanum tuberosum L.) Yield and Tuber Physiological Disorders Under Moderate and Severe Drought

Potatoes (<i>Solanum tuberosum</i> L.) are highly sensitive to water deficits, which compromise both yield and tuber quality, with russeting representing a major disorder that limits marketability. Film-forming antitranspirants, such as Vapor Gard (VG; di-1-<i>p</i>-menthene), may alleviate these effects by reducing transpirational water loss, but their effectiveness under different stress intensities remains uncertain. This study investigated the impacts of moderate and severe drought (targeted at 30% and 20% available water content, respectively) on plant water status, yield, and tuber physiological disorders in two varieties (Challenger and Russet Burbank), and assessed the extent to which VG could mitigate these impacts. Two pot experiments were conducted in a polytunnel using a factorial combination of soil-water regime and VG application. Drought reduced relative water content (RWC) by 30-36% and tuber yield by 29-61%, compared with irrigated plants. Under moderate drought, VG improved leaf RWC by 14-27% and increased yield by 37-67% relative to untreated drought-stressed plants across the two experiments, approaching levels achieved with irrigation. VG's influence on stomatal conductance was small and inconsistent. VG also consistently reduced russeting in the susceptible Challenger variety, while reductions in necrosis and jelly end rot were observed in Russet Burbank, indicating that disorder responses were variety dependent. Under severe drought conditions, VG provided little additional benefit for plant water status, yield, or disorder incidence. Overall, the results suggest that VG has potential as a management tool for reducing drought-related yield and quality losses in potatoes, particularly under moderate soil water deficit. However, further optimisation of application strategies is required to enhance consistency across environments.