Nonthermal microwave radiations affect the hypersensitive response of tobacco to tobacco mosaic virus

Objectives: The aim of the present study was to evaluate the effects of nonthermal extremely high-frequency microwave radiations in a plant-based bioassay, represented by tobacco plants reacting to tobacco mosaic virus with a hypersensitive response leading to the appearance of necrotic lesions at the infection sites. Design: This study was performed blind and different experimental protocols on tobacco plants inoculated with tobacco mosaic virus were used. Bio-objects: Tobacco plants (Nicotiana tabacum L. cultivar Samsun) carrying the resistance gene N against tobacco mosaic virus. Interventions: Tobacco plants or leaf disks were either directly or indirectly (water-mediated) irradiated using a medical device, designed for microwave resonance therapy. It produces nonthermal weak-intensity extremely high-frequency radiations, either modulated at extremely low frequency or in continuous flux of waves, coupled with a nonthermal red/near-infrared radiation. Outcome measurements: The working variable was the number of hypersensitive lesions per leaf disk. Results: Both direct and indirect nonthermal microwave radiations led to significant effects on the hypersensitive response of tobacco plants: modulated radiations generally induced a resistance increase, whereas a continuous flux of waves induced a resistance decrease with direct treatments only. Conclusions: Nonthermal microwave radiations are effective on the hypersensitive response of tobacco to tobacco mosaic virus and their low-frequency modulation seems to be more bioactive than the continuous-flux of waves, particularly in the indirect water-mediated treatments.