Abstract
This study aimed to assess the novelty of moringa (Moringa oleifera Lam.) leaf extract (MLE) as a natural biostimulant on bioactive compounds in lettuce. In autumn season of 2019 and 2020, MLE (6%) was foliar sprayed onto lettuce grown under glasshouse conditions. Vitamin C, total polyphenols, total chlorophyll content and nitrate accumulation in three lettuce cultivars (May King, Kobak, and Great Lakes) and some correlations among the bioactive compounds were assessed. The results in 2019 show that there was no significant differences in the total polyphenols (mg GAE 100 g−1 FW) and vitamin C (mg 100 g−1 FW) between treated and untreated plants, while in 2020 significantly higher vitamin C (mg 100 g−1 FW) and total polyphenols (mg GAE 100 g−1 FW) were recorded in the plants treated with 6% MLE. In contrast, in 2019 application of 6% MLE lowered nitrate content (mg kg−1) by 13% in May King, 23% in Kobak, and 44% in Great Lakes. Similarly, in the season of 2020 foliar application of 6% MLE reduced the leaf nitrate content by 16% in May King, 19% in Kobak, and 44% in Great Lakes. In the mean of varieties, the only significant difference in total polyphenol and vitamin C was in the Great Lakes variety grown in 2020 whereas no differences were found for the experiment of 2019. In the mean of years, the only statistical difference was recorded for the nitrate content in control of the Great Lakes variety by 44% lower nitrate in the treated plants with 6%MLE. Positive correlation was found between vitamin C and total polyphenol content, whereas nitrate had a negative regression slop to vitamin C and total polyphenol content in both experiments. The major total chlorophyll differences were found in the experiment of 2019, although no significant differences were found for the SPAD value of the experiment of 2020. In our 2 years study, there was a positive correlation between vitamin C and total polyphenol while negative correlation was found between vitamin C and total polyphenol to nitrate content in all the lettuce cultivars.
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