Effect of Smirnov‘s rhododendron and black mulberry seeds treatment by Low temperature plasma and electromagnetic field to seed germination and early plant development

Abstract

The effects of short term pre-sowing seed treatment by radio frequency electromagnetic field and cold plasma on two perennial woody plant species Smirnov‘s rhododendron (Rhododendron Smirnowii Trautv., RS) and black mulberry (Morus nigra L., MN) were estimated in this study. It is reported more substantial changes induced by pre-sowing seed treatment by physical stressors in perennial plant germination and plant development than it was reported previously for annual plants. The effects of stressors were species dependent – vacuum and electromagnetic field stimulated germination of freshly harvested seeds of RS, but negatively affected germination of fresh MN seeds; the response to cold plasma treatment was negative for RS, and positive for MN seeds. The changes induced by treatments in germination dynamics and yield were critically dependend on seed dormancy state: the same treatments induced positive effects in freshly harvested but negative effects – in after-ripened seeds. Longer term observations revealed that initially noticed effects persisted for more than one year, however shift from negative effects on germination to positive effects on plant morphometric traits took place over time. Some effects, characterised as distressful by changes in germination and seedling length after 13 months resulted in remarkable increase in RS growth: induced stem and root branching, increased leave number and surface area . These findings imply that such commonly used estimates for stressor effects as germination rate or seedling morphology not always can be regarded as sufficient parameters for qualifying the response to stressors (eustress or distress). At least for the perennial plants much longer observations are strongly recommended.