## 1 Introduction  
Macroalgae constitute an interesting marine biomass rich in diverse bioactive compounds, such as proteins (1-50% dry weight), lipids (0.3-5% dry weight), and carbohydrates (15-76% dry weight) [1]. More recently, marine polysaccharides present in the cell wall and the extracellular matrix of seaweed (alginate, agar, carrageenan, fucoidan, and laminaran) are the most extensively exploited components in cosmetics, nutraceutical, pharmacology, chemistry, and sustainable agriculture [2]. Polysaccharides derived from macroalgae are largely reported as bio-elicitors capable of inducing the natural defenses of plants to provide protection against a wide range of phytopathogens [3]. Sulfated carbohydrates (SPs) are most commonly used for diverse biological activities; for example, it has anticoagulant, antioxidant, antilipidemic, antithrombotic, antiviral, antihyperlipidemic, and immuno-inflammatory effects, as well as elicitor effects [4; 5]. They are found predominantly as fucoidans, carrageenan, and ulvans in red, brown, and green algae [6]. The sulfated fucans, ulvans, and galactans are widely studied in crop protection [3; 5; 7; 8]. The green algae contain a range of sulfated homo and heteropolysaccharides that are still rarely explored for their elicitor activities in agriculture. The ulvans (8 to 29% of the algal dry weight) are recognized by their high degree of sulfation [9]. These SPs are usually the most phycocolloid studied in various fields [9; 10]. Recently, the SPs from the genus _Codium_ were found to be an interesting bioactive compound, particularly used for medical purposes [11]. Currently, the _Codium_ genus (125 species) is classified as the second group of algae rich in SPs, after the _Ulva_ genus. _Codium fragile_ ssp. _fragile_ (formerly _Codium fragile_ ssp. _Tomentosoides_) is the most invasive green algae in the world [12; 13]. The cell walls of the _Codium_ species are mainly composed of sulfated mannans, arabinans, galactans, and arabin galactan-rich proteins (AGPs) [14; 15; 16]. AGPs, also known as arabin galactan type II (AG type II), are cell wall glycoproteins belonging to the hydroxyproline-rich glycoproteins (HRGPs) family. They are found principally in plants, some microorganisms, and have recently been detected in the seagrass species _Zostera marina_ L. [17; 18; 19]. Arabinogalactans from the green seaweed _Codium_ seem to be almost identical to terrestrial plants [16]. They are structurally characterized by the presence of a \(\beta\)-(1,3) and/or \(\beta\)-(1,6)- linked D-galactopyranose chain attached to hydroxproline (Hyp) residues [17; 18]. The non-reducing ends often consist of a main chain of L-arabinofuranose, L-arabinopyranose, D-mannose, D-xylose, D-glucose, L-rhamnose, L-fucose, D-glucosamine, and D-glucuronic acid [17; 19; 20]. Concerning the _Codium_ genus, the AGPs have been detected for the first time in _C. fragile_, which were composed mainly of linear (1\(\rightarrow\)4)-\(\beta\)- d-mannans, pyruvate arabingalactan sulfates (pAGS), and low amounts of HRGP [16]. A similar composition has been reported in the cell wall glycoproteins of _C. vermiana_[21]. Several studies have focused on the pharmaceutical applications of AGPs, but no previous research has investigated the use of these compounds in sustainable agriculture, especially as inducers of the natural defenses of plants. This approach is one of the new promising alternatives to chemical pesticides that focus on the use of natural products initiating the defense mechanisms leading to the stimulation of plant resistance against a wide range of phytopathogens. _Codium decorticatum_ (formerly _Codium elongatum_) is a dark green alga belonging to the family of Codiales, which grows on hard substrate in the lower mediolittoral zone. On the Moroccan coast, this species exhibits massive growth and large distribution. Despite their richness in bioactive compounds, they are not valorized locally [22]. As far as we know, the AGPs have never been isolated from _C.