The wetting of plants due to guttation (i.e., drops of xylem sap that exude onto the leaves) represents a potential risk for incidence and outbreak of pathogens. Here, we investigated the effect of air circulation on guttation of tomato leaves under dark and high humidity conditions. The tomato plants were grown in a container and pinched above the second truss and were then separately placed in a darkened and constantly humidified growth cabinet that was exposed to three levels of air circulation intensity (air velocities of 0.05 m s-1, 0.16 m s-1, and -0.29 m s-1). The evaporation rate increased in direct proportion to air velocity around the plants regardless of differences in leaf area. The guttation rate varied with leaf area
specially, tomato plants with small leaf areas secreted larger amounts of guttation water than those with large leaf areas. However, guttation was completely suppressed in both large and small leaves under well-circulated conditions (i.e., a velocity of -0.3 m s-1). This study indicates that air circulation reduces the wetting of plants by guttation under dark and high humidity conditions, which is likely to suppress the secondary spread of pathogens.