Elicitor potential of chitosan and its derivatives to enhancing greenhouse tomato (Lycopersicon esculentum Mill.) performance under deficit irrigation conditions

• Elicitors mitigate the negative effects of environmental stress on plants. • N-succinyl (NSU), a new chitosan derivative acts as an elicitor. • NSU improves tomato photosynthesis gas exchange, antioxidant, and ABA content. • NSU increases total and marketable tomato fruit yield under deficit irrigation. • NSU by increasing tomato fruit yield, result improving water use efficiency indices. Elicitors such as chitosan have been investigated for their potential to alleviate the adverse effects of environmental stress on plants. A split-plot experiment was conducted using a randomized complete block design with three replications to examine the effects of chitosan and its derivatives on the performance of greenhouse tomato cv. Dafnis under deficit irrigation (DI) conditions. The experimental factors included irrigation levels (well-watered; WW as control, moderate (MD) and severe (SD) deficit irrigation) as the main factor, and foliar application of elicitors as the sub-factor, which included a control group (untreated plants), chitosan, and the chitosan derivatives N-Succinyl (NSU) and N, O-dicarboxymethylate (NOD). The study found that chitosan and its derivatives, particularly NSU, resulted in increased levels of leaf abscisic acid (ABA), reduced stomatal conductance (gs), decreased transpiration rate (TR), and consequently an increase in net photosynthesis (P n ) under DI conditions compared to untreated plants, with increases of 18 %, 22.0 %, 18.9 %, 27.4 %, and 8 %, respectively. While the interaction between DI and elicitors had no significant effect on peroxidase (POD), lycopene content, or total flavonoid content (TFC), NSU increased catalase (CAT) activity by 66.9 % compared to the control under SD conditions. In SD conditions, chitosan resulted in the highest total phenolic content (TPC), while NSU was most effective under WW and MD conditions. Elicitors, especially NSU, mitigated the negative effects of SD on total and marketable fruit yield (TFY and MFY). Under SD conditions, NSU-treated plants exhibited the highest MFY (104.7 tons ha -1 ) and TFY (115.4 tons ha -1 ), representing increases of 54.2 % and 33.3 % from the control, respectively. Additionally, deficit irrigation improved water use efficiency (WUE) indices in tomato plants, by reducing water consumption. The application of elicitors further enhanced these indices by increasing leaf ABA, lowering g s and TR, increasing TFY and MFY, and decreasing unmarketable fruit yield (UFY). These results suggest that exploring chitosan derivatives for greenhouse tomatoes could enhance crop performance by improving WUE, fruit yield, and quality under deficit irrigation conditions. Based on these findings, NSU is proposed as a biological elicitor to mitigate the negative effects of water scarcity on tomatoes. However, further research is needed to assess its effectiveness in other crop plants.