Characterizing the Phytotoxic Effects of Hydrogen Peroxide on Common Microgreen Species and Lettuce Cultivars

Abstract

<jats:p>Hydrogen peroxide (H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>) is an oxidizing agent used to disinfect recirculated irrigation water during the production of organic crops under controlled environmental systems (e.g., greenhouses). To characterize the phytotoxic effects and define a concentration threshold for H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>, three microgreen species [arugula (<jats:italic>Brassica eruca</jats:italic> ssp. <jats:italic>sativa</jats:italic>), radish (<jats:italic>Raphanus sativus</jats:italic>), and sunflower (<jats:italic>Helianthus annuus ‘</jats:italic>Black Oil’)], and three lettuce (<jats:italic>Lactuca sativa</jats:italic>) cultivars, Othilie, Xandra, and Rouxai, were foliar sprayed once daily with water containing 0, 25, 50, 75, 100, 125, 150, or 200 mg·L<jats:sup>−1</jats:sup> of H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> from seed to harvest under greenhouse conditions. Leaf damage was assessed at harvest using two distinct methods: 1) the percentage of damaged leaves per tray and 2) a damage index (DI). Applied H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> concentrations, starting from 25 mg·L<jats:sup>−1</jats:sup>, increased the percentage of damaged leaves in every species except ‘Black Oil’ sunflower, which remained unaffected by any applied concentration. Symptoms of leaf damage manifested in similar patterns on the surface of microgreen cotyledons and lettuce leaves, while mean DI values and extent of damage were unique to each crop. Fresh weight, dry weight, and leaf area of all crops were not significantly affected by daily H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> spray. Identifying how foliar H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> damage manifests throughout the crop, as well at individual cotyledon or leaf surfaces, is necessary to establish an upper concentration threshold for H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> use. On the basis of the aforementioned metrics, maximum recommended concentrations were 150 mg·L<jats:sup>−1</jats:sup> (radish), 100 mg·L<jats:sup>−1</jats:sup> (arugula) for microgreens and 125 mg·L<jats:sup>−1</jats:sup> (‘Othilie’), 75 mg·L<jats:sup>−1</jats:sup> (‘Rouxai’), and 125 mg·L<jats:sup>−1</jats:sup> (‘Xandra’) lettuce.</jats:p>

Enhancement of Glucosinolate Formation in Broccoli Sprouts by Hydrogen Peroxide Treatment

“…In the trials with greenhouse-grown wild rocket, a leaf toxicity of 1000 mM H 2 O 2 was evident as scattered bleaching of the leaves within 24 h after application. This result was similar to the findings of Eicher-Sodo et al [ 66 ], who observed damage on arugula leaves after daily foliar H 2 O 2 treatment for 11 days using milder H 2 O 2 concentrations compared with our study. H 2 O 2 leads to programmed cell death as a defense mechanism of the plants [ 67 ].…”

Effects of Hydrogen Peroxide on Organically Fertilized Hydroponic Lettuce (Lactuca sativa L.)

“…At the lower treatment of H 2 O 2 , the conventionally fertilized plants had somewhat stunted growth (Figure 3a,b has the potential to indiscriminately damage healthy living root tissue, consequently reducing the fresh weight of lettuce heads in higher doses. Root damage may be the result of this phytotoxicity [17,[29][30][31]. However, when H 2 O 2 at 37.5 mg/L was added to organic fertilizer, this treatment performed as well as conventional fertilizer without H 2 O 2 .…”

Effects of Hydrogen Peroxide on Organically Fertilized Hydroponic Lettuce (Lactuca sativaL.)

“…As such, H2O2 has the potential to indiscriminately damage healthy living root tissue, consequently reducing fresh weight of lettuce heads in higher doses. Root damage may be the result of this phytotoxicity [24,25,26]. However, when H2O2 at 37.5 mg/L was added to organic fertilizer the organic fertilizer performed as well as conventional fertilizer without H2O2.…”