The relationship between leaf enclosure, transpiration, and upper leaf necrosis on Lilium 'Star gazer'

Upper leaf necrosis (ULN) on Lilium 'Star Gazer' has been shown to be a calcium (Ca) deficiency disorder. Initial symptoms of ULN tend to appear on leaf margins. Before flower buds are visible, young expanding leaves are congested and overlap each other on the margin. In the current study, we examined the relationship between leaf enclosure, transpiration, and upper leaf necrosis. We demonstrated that low transpiration rate and enclosure of young leaves played an important role in the occurrence of ULN. Young expanding leaves are low transpiration organs. The younger the leaf, the lower the transpiration rate and Ca concentration. Leaf enclosure further reduced transpiration of these young leaves and promoted ULN. Upper leaf necrosis was suppressed by manually unfolding the leaves using a technique we refer to as artificial leaf unfolding (ALU). ALU minimized leaf congestion, exposing leaves that were previously enclosed. We demonstrated that the effect of ALU was not the consequence of thigmomorphogenesis, as ULN was not reduced by mechanical perturbation in lieu of ALU. With ALU, transpiration of upper leaves was significantly increased and Ca concentration of the first leaf immediately below the flower buds was increased from 0.05% to 0.20%. We concluded that leaf enclosure promoted ULN occurrence, and ALU suppressed ULN primarily by increasing transpiration. The use of overhead fans to increase airflow over the tops of the plants significantly reduced both ULN incidence and severity.