Title : Low-temperature plasma: A novel technology for improving productivity and seed safety of horticultural crops
Abstract:
Low-temperature plasma (LTP), a weakly ionized noble gas or ambient air consisting of free electrons and positively charged ions, has been shown to break seed dormancy, enhance plant growth and yield, and ensure seed safety by mitigating seed-borne pathogens. This study evaluated LTP at 7 kV, with a pulse width of 1 μs and a frequency of 5 kHz, for the purposes: i) to enhance seed germination, growth, and nutrient quality of microgreens, and ii) to mitigate seed-borne pathogens on pepper and spinach seeds.
In Experiment 1: Seeds of fifteen microgreen species were exposed to either Argon (Ar) or Helium (He) LTP for 0 (Control), 30, 60, or 90 seconds. The treated and untreated seeds were then assessed for moisture imbibition rates. Additionally, a greenhouse experiment assessed mustard greens’ seeds exposed to either He or Ar LTP for 0 (Control), 30, 60, or 90 seconds for seedling growth and nutrient profiles.
In Experiment 2: Pepper seeds coated with bacteria Xanthomonas campestris pv. vesicatoria and spinach seeds, with and without infection from Stemphyllium botryosum, were treated with He LTP for 0 (Untreated Control) or 15 seconds. Similarly, fungal conidia of S. botryosum strain 406 were either exposed to LTP or not and then cultured on V8 juice agar. Both treated and untreated seeds were incubated at 25 ± 2°C for germination.
Results from Experiment 1: Radish, buckwheat, and scallion seeds treated with He LTP for 90 seconds exhibited significantly improved moisture imbibition, while spinach and Pac Choi showed similar response in the 30-second treatment with Ar. Cilantro, scallion, and mustard greens responded positively to both Ar and He LTP. Broccoli, cabbage, and fenugreek showed no response. In the greenhouse trial, the Ar 30-second treatment increased plant height by 98% compared to the Control, while the He 60-second treatment increased the growth rate by 94.3%. Biomass improved by 78.2%, 63.2%, and 51.6% for Ar 60 seconds, He 60 seconds, and Ar 30 seconds treatments, respectively. The He 90 seconds, Ar 60 seconds, and He 60 seconds treatments enhanced total phenolic content by 32.6%, 27.6%, and 24.8% over the Control. Antioxidant power increased by 24.3%, 23.6%, and 23.2% with Ar 90 seconds, Ar 30 seconds, and He 90 seconds treatments, respectively, compared to the Control.
Results from Experiment 2: Whether infested with the pathogen or not, the treated seeds showed a higher germination percentage, though not statistically significant. More pronounced effects of LTP were observed on the pathogens. The S. botryosum conidia exposed to plasma germinated but did not exhibit significant mycelial growth compared to the untreated conidia, which grew normally. The LTP treatment suppressed mycelial growth, preventing conidia production in the treated fungus. Additionally, X. campestris pv. vesicatoria exposed to He LTP displayed distorted and damaged cell walls, leading to bacterial death. In contrast, the untreated bacteria remained rod-shaped and intact. The research concludes that low-temperature plasma is a novel green technology for improving crop seed germination, plant growth, yield, and nutritional value. Furthermore, LTP effectively sanitizes seeds by destroying seed-borne pathogens. This research was supported by NSF EPSCoR RII Track 1 Grants OIA – 1655280 and 2148653 and NASA EPSCoR 80NCCS21M0139.
