Microbiota of seeds and seedlings’ rhizosphere of Rhododendron smirnowii grown from seeds treated with cold plasma, vacuum and electromagnetic field

Abstract

We have demonstrated recently [1] that pre-sowing treatment of Rhododendron smirnowii Trautv. seeds with electromagnetic field (EMF), vacuum and cold plasma (CP) strongly affects germination kinetics and seedling growth. Seed treatment with EMF and vacuum increased germination percentage up to 70% but CP treatments negatively affected germination. However, these methods were not estimated to have a forceful effect on microbiological cleanliness of the seeds. We succeeded to isolate 11 species of fungi, where 6 were identified as plant pathogens (Sporocadus sp., Fusarium avenaceum, Alternaria alternata, Cladosporium cladosporioides, Botrytis cinerea) and other 5 were assigned to Penicilllium genus. Differences in composition of endophytic mycobiota in seeds were statistically not significant. Long term observations revealed that seedlings grown from CP treated seeds, characterized by negative effects on germination (decreased germination percent by 23%), 13 months after sowing had considerably larger (by 69%) height, more branches and better developed roots, substantially larger (7.4-fold) total leaf surface area per plant in comparison to control plants. We have tested the hypothesis that plants grown from the treated seeds induce changes in soil microorganism community promoting plant growth. The obtained results showed that physical treatments affected the amount (colony forming units (CFU)) of rhizospheric bacteria in roots: control samples had less CFU than after treatment either with EML, CP or vacuum. 104 bacteria isolates were collected from roots and 40 isolates from soil. DNA sequencing results showed that the dominant bacterial groups were Agrobacterium sp., Bacillus sp., Burkholderia sp., Paenibacillus sp., Pseudomonas sp., Rhizobium sp