A case study of seed biopriming and chemical priming: seed coating with two types of bioactive compounds improves the physiological state of germinating seeds in durum wheat

The use of biostimulants in plants is among the novel and integrated approaches in plant protection to increase crop tolerance to multiple biotic and abiotic stresses. In this context, seed coating with thyme essential oil and the endophytic bacterium Paraburkholderia phytofirmans was performed on durum wheat seeds in order to investigate their effects on germination of seeds and seedling growth. An in vitro assay was used to evaluate their effects on acidification, amylolytic activity in seeds, and on the peroxidases activity and phenolic content in wheat seedlings. To ascertain the endophytic behaviour of P. phytofirmans , Gfp (green fluorescent protein) marked mutant (PsJN*) was used for bacteria quantification in roots, stems and leaves using Real-Time PCR. Afterwards, a hydroponic culture system was used to study their effect on plant growth at an advanced stage. Seed coating with both agents resulted in the priming of seeds, illustrated by (i) earlier and higher acidification and amylolytic activity of seeds, (ii) induced changes in peroxidases activity and total phenolic content in wheat seedlings, (iii) an increased germination rate, and (iv) increased shoot and root development. The systemic spread of bacteria was confirmed within 7 days. The difference between the effects of P. phytofirmans and thyme oil on seed acidification, plant peroxidases activity, phenolic content, and shoot and root development suggests that they employ different mechanisms for seed priming and plant growth promotion in wheat plants.