Heat treatment of plant propagation material for the control of fire blight.
The thermal sensitivity of Erwinia amylovora was determined at 45° and 50°C. In vitro assays with 8 different strains showed that thermal death times did not exceed 70 min at 45° and 50 min at 50° (95% confidence interval). Heat treatments of naturally infected apple and pear shoots were performed using a moist and a dry heat procedure. When shoots were wrapped in wet cotton cloths (wet heat) and maintained in an incubator, no bacterial growth could be detected after an incubation of 5 h at 45°. When shoots were sealed in polythene bags and immersed in water (dry heat), no E. amylovora could be isolated after an immersion of 3 h at 45°. Incubation at 50° for 1-2 h in either condition did not eradicate the pathogen entirely. The failure rate of grafts using budwoods treated at the effective time-temp. combinations did not exceed 25%. It is concluded that the use of thermotherapy techniques for controlling E. amylovora in propagation material of apple and pear might be possible.