Mitigation of drought stress in three squirting cucumber ecotypes through foliar application of different seaweed extract mixtures as a biostimulant

• Two sequential field experiments were conducted, with the first (2019–2020) focusing on assessing the drought mitigating effects of seaweed extracts from Gracilaria corticata and Acanthophora spicifera , both individually (G and A) and combined (GA), on three squirting cucumber ecotypes. • The second experiment (2020–2021) focused initially on using an autoclaved extraction method to prepare GA in a 50:50 ratio, and subsequently six biofertilizer treatments (AGA1, AGA2, AGARB, AGARBCMS, FS, and control) were scrutinized to determine their effectiveness in moderating drought stress on the same three squirting cucumber ecotypes. • Considering 12 morpho-physiological traits, the GA-treated plants experienced less destructive consequences of water scarcity, albeit both the fully irrigated ecotypes from Spain and Iran yielded the highest fruit yield of 7422.7 and 6370.8 g ha -1 among 36 treatments. • Among the six biofertilizers, the AGARBCMS developed from a tertiary combination of AGA extract, rice bran extract, and cow manure slurry extract, was the superior in mitigating drought stress in all three ecotypes during the second experiment. • From a practical view, the AGARBCMS-treated plants of three ecotypes yielded the maximum fruit yield under normal irrigation condition, with the Spanish ecotype producing the highest value of 6427.9 g ha -1 . In a pioneering effort, two consecutive field experiments were conducted, with the first one (2019–2020) focusing on the performance of foliar-applied aqueous extracts of two types of red seaweeds ( Gracilaria corticata and Acanthophora spicifera ), both individually (G and A) and in combination (GA), on three ecotypes of squirting cucumber ( Ecballium elaterium ) from Iran, Spain, and Britain, under varying levels of drought stress (100 %, 70 %, and 50 % ETc). After identifying GA as the most effective biostimulant, the second field experiment (2020–2021) delved into the use of an autoclaved extraction (AE) method to extract GA (in a 50:50; w/w ratio), followed by the preparation and evaluation of six different biofertilizer (BF) treatments (i.e., AGA1, AGA2, AGARB, AGARBCMS, FS, and distilled water as control) on the same three ecotypes under the three levels of drought stress via a foliar method. Both experiments measured 12 morpho-physiological traits. Based on the first experiment results, the GA treatment (2.0 L/ha) significantly improved various parameters such as fruit yield, relative water content (RWC), antioxidant enzyme activities, and osmolyte accumulation particularly in the Iranian and Spanish ecotypes. According to the clustered heatmap and PCA, the 36 treatments were clustered into three main categories. Interestingly, the GA treatment in both Spanish and Iranian ecotypes (“100+S+GA” and “100+I+GA” respectively), under normal irrigation yielded the highest fruit yield of 7422.7 and 6370.8 g ha -1 among all 36 treatments. In the subsequent phase, a tertiary combination of AGA extract, rice bran (RB) extract, and cow manure slurry (CMS), known as “AGARBCMS” (2.0 L/ha), was the most effective biofertilizer in mitigating drought stress in the three ecotypes compared to other treatments. By improving membrane stability, osmotic adjustment, antioxidant defense, and increasing fruit yield, this treatment has shown to significantly reduce drought-induced oxidative stress. Through the clustering of the 54 treatment, the “50+I+AGARBCMS”, “50+I+AGARB”, “50+S+AGARBCMS”, and “50+B+AGARBCMS” treatments exhibited promising results in terms of having higher concentrations of key features (e.g., α-Tocopherol, proline, soluble sugar content, APX, SOD, CAT, glutathione reductase, and glycine betaine) while the “100+S+AGARBCMS”, “100+I+AGARBCMS”, and “100+B+AGARBCMS” treatments yielded the highest fruit yields of 6427.9, 6001.0, and 5415.7 g ha -1 , respectively. Notably, all three ecotypes that were treated with distilled water exhibited maximum levels of EL under water deficit stress conditions, indicating a significant level of oxidative stress and membrane damage. These findings emphasized the potential of AGARBCMS as a cost-effective, eco-friendly, and multi-functional biostimulant for enhancing drought resilience and productivity of not only squirting cucumber but also other herbal or crop plants in open-field cultivation.