A method for estimation of population densities of ice nucleating active Pseudomonas syringae in buds and leaves of mango

Active ice nucleation strains of Pseudomonas syringae pv. syringae have been associated with a necrotic disease in mango trees growing in Málaga (southern Spain). In this paper a simple multiple‐tube test is described to estimate the number of active ice nucleation bacteria associated with plant tissues and, also from suspensions of isolated bacterial strains. This method is based on the most probable number technique developed for microbiological analysis of water. The tube test presented a higher detection sensitivity of active ice nuclei than the traditional drop‐freezing test, because a larger amount of plant material could be analysed routinely. Both methods demonstrated a similar accuracy. A high correlation was obtained between the tube test‐estimated number of ice nuclei and populations of Ps. syringae ‐like organisms enumerated on King's agar B.