A medium-scale volume dielectric barrier discharge system for short-term treatment of cereal seeds indicates improved germination performance with long-term effects

Abstract

Atmospheric pressure plasma has the potential of being applied in pre-harvest processes as a sustainable technology for seed and plant treatment. In this study, a medium-scale volume dielectric barrier discharge reactor with a power density of 53.5 mW/cm3 was developed and applied for continuous treatment of larger amount of seeds. Within the argon plasma, reactive oxygen and nitrogen species were observed by optical emission spectroscopy. Short-term plasma treatment in the range of seconds of wheat and barley seeds revealed improved germination performance accompanied by altered seed surface properties. Depending on the exposure time, plasma displayed a positive impact on maximum germination and germination speed in both species. In line with this, the t50 values were significantly decreased for plasma treated seeds compared to untreated seeds for wheat and barley. Cumulative germination was enhanced from 20% up to 53% after 27 h of germination for wheat seeds treated from 10 s to 60 s with plasma. Barley seeds respond to the short plasma treatment times with increased germination of 10%–23% after 24 h observation time. Moreover, the seed surface of both plant species became more hydrophilic after plasma treatment supported by a decrease in the water contact angle and an increase in hydrophilic functional groups being detected by x-ray photoelectron spectroscopy. Water uptake by seeds was moderately increased after 2 h of imbibition for both plant species. The positive effects of plasma treatment on germination performance were still detectable after storage of seeds for one and two months.

Surface Modifications of Wheat Cultivar Bologna upon Treatment with Non-Equilibrium Gaseous Plasma

“…While these values are comparable to our own, as seen in Figure 2, the authors [15] required a sufficiently longer treatment time due to the differences in the plasma systems (about a minute). Another group [14] also showed an increased proportion of O-containing functional groups on the seed surface after treatment with an atmospheric-pressure DBD using argon. The O/C ratio more than doubled after 60 s of plasma treatment.…”

“…Bormashenko et al, who also used an IC RF plasma at low pressure, achieved super-hydrophilicity after 15 s of treatment [16]. Several other publications, using variations of atmospheric pressure DBD, mainly reduced the WCA to the range of about 40-60 • [14,20,24,45], or in one case, only 87 • [23], at the selected treatment conditions. Super-hydrophilicity was only achieved at much longer treatment times, such as 3 [19] or 15 min [15].…”

“…When oxygen is present in the processing gas, new oxygen-containing functional groups become introduced into the predominantly hydrocarbon structure of the cuticle. Using X-ray photoelectron spectroscopy (XPS), this was shown in wheat seeds treated by atmospheric-pressure DBDs using argon [14] or helium [15] as processing gases. Time-of-flight secondary ion mass spectrometry also indicated the presence of new O-rich functional groups in wheat seeds after low-pressure IC RF air plasma treatment [16].…”

“…The modified physicochemical properties of the wheat seed surface affect its wettability. A decreased water contact angle (WCA) was measured after a variety of plasma treatments, including DBDs [14,15,19,20], a glow discharge in argon [11], and an IC RF discharge [16]. One group used ethylene glycol and diiodomethane contact angles to further assess the hydrophilicity of the wheat seed's surface [20].…”

“…One group used ethylene glycol and diiodomethane contact angles to further assess the hydrophilicity of the wheat seed's surface [20]. In relation to increased wettability, water uptake of the seeds commonly increased as well [10,[14][15][16]21].…”