Frost Injury of Tender Plants Increased by Pseudomonas syringae van Hall1

Abstract

Abstract Pseudomonas syringae van Hall, an ice nucleation active (INA) bacterium, increased frost susceptibility of tomato ( Lycopersicon esculentum Mill.) and soybean ( Glycine max L.) when sprayed on leaves prior to low temperature stress. Tomato and soybean plants inoculated with INA bacteria were nucleated and frozen at −4° and −5°C respectively. Control plants that were free of INA bacteria supercooled and survived to −8°. A threshold INA bacterial concentration of about 4 × 10 5 cells/ml was necessary for ice nucleation. Ice nucleating active bacteria preconditioned at 2° showed a marked increase in efficiency of ice nucleation. Preconditioned INA bacteria had ice nucleation temperatures 5° higher than INA bacteria held at 21°.