# Characterization and Optimization of a Conical Corona Reactor for Seed Treatment of Rapeseed
## 3 Results and Discussion
### Treatment of Rapeseed
For higher duty cycle values, the period of plasma on was increased. As indicated in Figure 4d, the increase in voltage duty cycle might also lead to a higher production of RONS. Therefore, seeds treated with higher duty cycle values were not only exposed to plasma for longer periods but also might be exposed to higher amounts of reactive species. The reduction in water contact angle on the seed coat is often associated with an improvement in water uptake by the seed. The ruptures caused by plasma treatment on the seed coat of artichoke seeds reported by [PERSON] et al., 2018 [45], were pointed out as one of the responsible aspects that led to increased water uptake. Other studies also reported cracking of the seed coat and investigated its correlation with the increased water uptake and consequent improvement in germination [48; 49]. In addition to morphological changes at the seed coat, another factor that contributes to improved germination is the surface activation by incorporation of radicals via etching [44]. Figure 6: Comparison of the temperature measured inside of the empty reactor (center bottom of the Petri dish) after 3 min and the temperature obtained on the seed surface after treatments for 3 min using different duty cycle values. In this study, the germination rate of rapeseed treated with the funnel reactor using different duty cycles was investigated. Figure 8 shows the germination curves for gas control and treated seeds with different duty cycles (D = 10%, 50%, and 90%). Acceleration in germination below 22 h of observation time could be detected for all treatment conditions (D = 10%, 50%, and 90%). A maximum increase in germination was observed after 17 h of germination time, where an increase of around 20% was obtained for D = 10%, 50%, and 70% and an increase of around 27% for D = 90%. This moderate increase in germination caused by plasma treatment contrasts with the considerable decay in WCA for all duty cycle values. Such discrepancy was also reported and discussed in previous works [18,19]. It indicates that other factors besides improvement in surface wettability play a role when improving seed germination. Some reactive species, such as hydrogen peroxide and nitric oxide, might impact metabolic processes in plants [50]. Such species can be generated by further reactions between plasma-produced ROS and water and be taken up during the imbibition process [18]. Seed germination tests can provide a variety of information, such as maximum germination capacity (Gmax), mean germination speed (t50), and germination uniformity (U25-75) [19]. The indices can be extracted from the germination curve acquired for different  
Figure 8: Germination acceleration of treated rapeseed (3 min) using different duty cycles. Germination curves were fitted with the Hill function. Figure 7: Water contact angle of rapeseed treated with the funnel reactor for 3 min using different voltage duty cycle values. (*) Represents a statistically significant difference (\(p<0.001\)). times until maximum germination is reached. The seeds of rapeseed used in this study presented high maximum germination (G\({}_{\text{max}}\)) of around 90%. All the values extracted from the germination curves are displayed in Table 1. For all conditions, maximum germination was achieved within 48 h and the seeds treated with a duty cycle of 70% exhibited a significantly higher G\({}_{\text{max}}\) (around 96%) when compared to gas control (Table 1). It is important to highlight that plasma treatment did not negatively affect the maximum germination value of rapeseed for any of the tested treatment conditions. [PERSON] et al., 2017 [PERSON] et al., 2017, also investigated the effects of a corona discharge on rapeseed. An impact of treatment time on the maximum germination was detected, where an improvement was observed for shorter treatment times (1 and 2 min) and a significant reduction for 3 min treatment.