Possible use of thermotherapy of plant propagation material against Erwinia amylovora
Studies have been carried out to investigate the heat sensitivity of Erwinia amylovora (EPPO A2 quarantine pest), both in vitro and in planta, at 45 °C and 50 °C, and to examine the effect of these temperatures on the viability of pear and apple budwood. During in vitro assays with eight different strains, it has been shown that thermal death times did not exceed 70 min at 45 °C and 50 min at 50 °C (95 % confidence interval). Thermotherapy of naturally infected apple and pear shoots have been performed using a moist and a dry heat procedure. For the moist procedure, during which plants are wrapped in wet cotton cloths and maintained in an incubator, no bacterial growth could be detected after an incubation of 5 h at 45 °C. When shoots were sealed in polyethylene bags and immersed in water (dry heat), no bacteria could be isolated after an immersion of 3 h at 45 °C. However, incubation at 50 °C for 1-2 h, in either humid or dry condition, did not eradicate E. amylovora completely. The rate of failure of grafts using budwood treatment at the effective time-temperature combinations did not exceed 25 %. The authors concluded that these results confirmed the feasibility of controlling Erwinia amylovora in apple and pear by thermotherapy. A treatment of 5 h at 45 °C in incubator or of 3 h at 45 °C in a water bath, as described above, is simple and flexible enough to be recommended, for example before shipping of plant material or prior to the release of fire-blight-resistant varieties which could transmit the bacteria without showing any symptoms.
Sources
Keck, M.; Chartier, R.; Zislavsky, W.; Lecomte, P.; Paulin, J.P. (1995) Heat treatment of plant propagation material for the control of fire blight.
Plant Pathology, 44 (1), 124-129.