Foliar chitosan–selenite formulation improves wheat seedling growth under NaCl irrigation

Salinity limits wheat productivity through osmotic stress, ion toxicity, oxidative damage and disruption of photosynthesis. Chitosan and selenium are used as biostimulants, but formulations combining them have rarely been evaluated in wheat. This study examined whether a foliar chitosan–selenite formulation (Cs–Se), prepared by ionotropic gelation of chitosan with tripolyphosphate and sodium selenite, improves the growth of wheat seedlings irrigated with NaCl solutions, and how the response relates to photosynthetic pigments, proline, the leaf distribution of chitosan and the expression of stress-related genes. Two wheat cultivars (Chamran and Mehregan) were sprayed with chitosan (Cs), sodium selenite (Se) or Cs–Se and irrigated with 0, 150 or 300 mM NaCl. Irrigation with 300 mM NaCl reduced plant height and fresh and dry weight in both cultivars, whereas pigment contents decreased in control plants but, except for chlorophyll b in Se-treated Chamran plants, not in treated plants. Cs–Se gave the highest fresh weight at every NaCl level (at 300 mM NaCl, 0.268 vs 0.198 g in Chamran and 0.208 vs 0.129 g in Mehregan), but for plant height, SPAD chlorophyll meter value and dry weight it was often equivalent to Cs. Proline increased with NaCl in Se- and Cs–Se-treated plants. Growth traits correlated only weakly with pigment contents ( r ≤ 0.30). Fluorescein isothiocyanate (FITC)-labeled chitosan produced strong fluorescence in the epidermis and weaker fluorescence in the mesophyll. In control plants, NaCl decreased TaAPX , TaCAT , TaNHX1 , TaHKT9-7D and TaPXPAO transcript levels and increased only TaP5CS , whereas at 300 mM NaCl the Se and Cs–Se treatments increased TaCAT , TaNHX1 and Ta4CL3-6B transcript levels in both cultivars relative to control plants. Foliar Cs–Se improved seedling growth under NaCl irrigation, most clearly fresh weight. The selenite-containing treatments increased the transcript levels of several genes putatively involved in antioxidant defense, Na⁺ transport, phenylpropanoid metabolism and, with Cs–Se, polyamine catabolism; the functional consequences were not measured. FITC-labeled chitosan was located mainly in the epidermis, which shows association of chitosan with the leaf but not uptake of selenium or of the formulation. Physicochemical characterization of the formulation and field studies are needed to establish its practical value.