Influences of Ice Nucleating Active Bacteria on the Frost Injury of Crops

Frost injury of crop is affected considerably by ice nucleating active (INA) bacteria. Characteristics of ice nucleation activity of three kinds of INA bacteria were investigated by freezing the water droplet suspended with INA bacteria, the leaf disks and the intact seedlings of cucumber inoculated with INA bacteria. INA bacteria used in the study are Pseudomonas syringae pv. mori S8110-1 (PS+), Pseudomonas syringae pv. mori S6801 (PS-) and Erwinia herbicola M1(Eh). Freezing temperatures of droplets (20μl) of the suspensions which have concentration of 108cells/ml of PS+, Eh and PS- were -3.0--5.0, about -5.0 and -6.0°C respectively, while that of distilled and deionized water was -7--15°C and less. The freezing temperature was affected greatly by concentration of INA bacteria. Relationship between the freezing temperature and the concentration of INA bacteria was proportional. Furthermore, suspension of higher concentration has frozen in shallower range of temperature than that of lower concentration. Characteristics of freezing pattern of leaf disks cut off from the second and third leaves of cucumber seedlings at 24hr and 48hr after INA bacterial inoculation were similar to that of the suspensions. Freezing temperatures of intact cucumber seedling were also increased by inoculation of INA bacteria. The higher the concentration of INA bacteria was, the higher the freezing temperature was.