In vitro assessment of Cowpea cv. GIZA-18 forage grown from low-pressure radiofrequency plasma-treated seeds under salt stress

Soil salinization, as one of the most critical phenomena of climate change, poses significant challenges to agricultural productivity, especially in arid and semi-arid regions like Egypt's Nile Delta surrounding area. Forage crops, such as cowpea (Vigna unguiculata), demonstrate relative tolerance under harsh conditions; however, its productivity and nutritional quality may be compromised by abiotic stress. Plasma as an advanced and precise technology showed promising results in agriculture. However, insights into the role of plasma in stimulating plant tolerance to salinity while maintaining high-quality products require in-depth investigations and studies. This study evaluated the effects of plasma application as a recent method for seed priming on forage productivity, anti-nutritional factors (ANFs), and in vitro degradability dynamics of cowpea cv. GIZA-18 under salinity stress. Seeds were exposed to low-pressure radiofrequency plasma (13.56 MHz, 60 W) for 0.0 (control), 1.0, 2.0, and 3.0 min (min) and seedling growth traits were evaluated under wire house conditions. Next, in two seasons of 2022 and 2023, plasma-treated seeds for 0.0, 1.0, and 2.0 min were cultivated under field conditions in soil with three levels of salinity expressed in electrical conductivity (EC) of 3.0, 5.5, and 7.0 dS m⁻¹. Findings exhibited that chlorophyll concentration, length, and weight of cowpea seedlings were improved by the application of different doses of plasma. Plasma dose of 1.0 min under moderate salinity (EC5.5) resulted in promising and established outputs, as the improvements in forage yield amounted to 47.0 and 146.1% in the first and second season, respectively. Results also demonstrated that based on the dry matter (DM) basis, plasma treatment significantly reduced ANFs, with 1.0 min exposure decreasing tannins by 15.72% (from 9.54 mg /100 g DM to 8.04 mg /100 g DM) and saponins by 48.39% (from 1.55 g/100 g DM to 0.80 g/100 g DM). At high salinity (EC7.0), crude protein increased to 166.9 g/kg in plants produced from 1.0 min treated seeds. Cowpea forage grown from plasma-treated seeds for 1.0 min showed significantly higher in vitro degradable dry matter (IVDDM), in vitro degradable neutral detergent fiber (IVDNDF), and in vitro degradable acid detergent fiber (IVDADF) compared to both untreated and 2.0-min treated seeds. Fermentation kinetics indicated that the 1.0-min of plasma treatment significantly reduced gas production per gram of DM and gas production per gram of organic matter (OM) in comparison to untreated seeds (0.0 min). Additionally, plants grown from seeds treated for 2-min had significantly higher ammonia concentrations compared to those grown from untreated seeds or those treated for 1.0 min. In brief, we can conclude that plasma technology can contribute to enhancing the establishment of cowpeas grown in saline soils, improving seedling growth, salinity tolerance, and productivity. Further, the In Vitro evaluation confirmed plasma's efficacy in ameliorating the nutritional quality of cowpea forage under salt stress. Accordingly, cowpea growers are advised to subject the seed to plasma for 1.0 min immediately prior to sowing in saline soil for keeping forage productivity and quality.