Ice Nucleation Activity of Strains from Pseudomonas syringae Pathovars atrofadens and syringae, Mainly Isolated from Cereals

Ice nucleation activity was determined in 14 strains of Pseudomonas syringae pv. syringae and 16 strains of Pseudomonas syringae pv. atrofadens. mostly isolated from cereals. The majority of the sxringae-sivAms (85%) possessed ice nucleation activity, with 64% being highly active. In contrast, most of the atrofaciens-ʹSXra.mʹi (69%) showed no ice nucleation activity, and only 19% were highly active. The results obtained could be confirmed by determining the nucleation frequency in the temperature range from - 3 to —10 C, The data indicate that the capability for ice nucleation might help epiphytic bacteria to colonize leaf surfaces by the release of plant nutrients at mild and short-term frosts. On the other hand, those Ps. syringae pathovars that can infect and ingress into leaves, are not apparently dependent on ice nucleation activity for pathogenesis