Heat treatments to kill Pseudomonas syringae pv. actinidiae on contaminated pollen

Various combinations of heat, time and relative humidity (RH) were tested for their ability to kill Pseudomonas syringae pv. actinidiae (Psa), the cause of kiwifruit canker, on freshly harvested anthers artificially contaminated with this bacterium. Pollen viability and Psa survival were tested after treatment. Although short durations at high temperatures and high RH did kill Psa, these treatments were also lethal to pollen. When RH was reduced, the time before pollen viability was lost increased, but Psa survival was also enhanced. The most promising treatment was 35°C at a RH of 50% or less, at which pollen viability was not affected even after 20 h, but Psa did not survive when applied at 10 6 cfu/ml. Modelling suggests that extending the time of treatment would kill higher concentrations of Psa. The mechanism for Psa death at 35°C is probably by a combination of heat and desiccation.