Enhancing Drought Stress Tolerance in Chickpea Genotypes: Impact of Grape By-Product Amendments on Morpho-Physiological Parameters and Phenolic Composition

Water deficit stress poses significant challenges to chickpea production, affecting plant growth, physiological parameters, and overall crop yield. This study aimed to identify drought-tolerant chickpea genotypes and evaluate the potential of grape by-product amendments to alleviate water deficit stress. Two trials were conducted. The first one investigated the agronomic evaluation of eight chickpea genotypes (G1–G8) cultivated in three different soils to identify drought-tolerant genotypes and the poorest soil. Three chickpea cultivars, G2 (Nour), G3 (Rebha), and G4 (Bochra), were selected for their identified moderate drought tolerance and their status as widely available commercial genotypes in Tunisia. In the second trial, two grape by-product amendments were tested for their ability to enhance the drought tolerance of the selected chickpea genotypes in the poorest-performing soil. Under water deficit conditions, the stalk amendment increased the relative water content (RWC) of the drought-tolerant genotype Nour by approximately 61% compared with the non-amended treatment and a 90% improvement in SPAD chlorophyll readings in Nour under water deficit conditions. Among the tested genotypes, Nour maintained the highest photosynthetic efficiency under drought, with Fv/Fm reaching approximately 0.62 following stalk amendment, indicating improved preservation of PSII functionality. Polyphenol profiling indicated that both drought stress and soil amendments modulated the accumulation of phenolic compounds. Enhanced polyphenol levels, particularly under stalk amendment and water deficit, suggest activation of antioxidant and protective metabolic pathways involved in plant stress defense. Thus, grape by-products, especially stalk residues, demonstrate potential as sustainable soil amendments to mitigate drought stress effects in chickpea through improvements in plant–water status, photosynthetic efficiency, and stress-responsive metabolism.