This study aimed to evaluate the efficacy of a biological mixture comprising the fungus Trichoderma spp. and Chitosan in controlling Powdery Mildew, caused by the pathogen Blumeria graminis f.sp. tritici, on wheat (Triticum aestivum L.). Powdery mildew is considered one of the most destructive fungal diseases affecting wheat globally. Its symptoms begin with the appearance of pale grayish-white spots on the leaves, which develop into a characteristic powdery appearance on the upper, and subsequently the lower, leaf surfaces. The disease can reduce yield by up to 30-40% in severely infected fields. The infection spreads rapidly under moderate humidity and relatively low temperatures. Severe infection leads to the desiccation of leaves and stems, significantly reducing the photosynthetic area.

The study evaluated the efficacy of Trichoderma alone in controlling the disease, assessed the impact of Chitosan as a bio-elicitor for resistance against powdery mildew, and investigated the synergistic effect of the biological mixture (Trichoderma + Chitosan) in reducing infection severity. It also aimed to determine the optimal Chitosan concentration (0.5%, 1.0%, and 1.5%) when combined with a fixed Trichoderma concentration of 1×10⁸ spores/mL. The study relied on an extensive scientific review demonstrating that Trichoderma possesses multiple biocontrol mechanisms, including mycoparasitism, antibiosis, competition for nutrients and space, and the production of fungal cell wall-degrading enzymes such as chitinases and glucanases. Furthermore, it has the ability to induce systemic resistance in the plant and enhance its growth by increasing nutrient availability. Chitosan, a natural polymer derived from chitin, exhibits antifungal activity through three main mechanisms: altering the permeability of the fungal plasma membrane leading to the leakage of intracellular contents; acting as a chelating agent that reduces the availability of essential elements required for fungal growth; and penetrating fungal cells to bind with their DNA, thereby inhibiting the synthesis of essential proteins and enzymes.

Disease severity was assessed using a numerical scale (0-9) and McKinney's index. Physiological and chemical parameters were measured, including chlorophyll content (using a SPAD meter), phenolic compounds (using the Folin-Ciocalteu method), and peroxidase activity. Data were statistically analyzed using SAS software, and means were compared using the Least Significant Difference (LSD) test at a significance level of P ≤ 0.05.

The results demonstrated the high efficacy of the biological mixture in controlling the disease. Trichoderma alone reduced disease severity by 42.3%, indicating its direct competitive ability against the pathogenic fungus. Chitosan exhibited a concentration-dependent effect, with the 0.5% concentration achieving a 33.3% reduction, 1.0% achieving 47.4%, and the 1.5% concentration recording the highest individual reduction rate of 51.3%. However, the combined treatments proved significantly superior to using either agent alone, indicating a true positive synergistic effect. Treatment T6 (Trichoderma + 0.5% Chitosan) achieved a 59.0% reduction, and T7 (Trichoderma + 1.0% Chitosan) achieved 73.1%. The T8 treatment (Trichoderma + 1.5% Chitosan) yielded the best overall result with a 75.6% reduction, decreasing the disease severity from 7.8 in the control treatment to merely 1.9. This synergy is attributed to Trichoderma providing direct protection and biological competition against the pathogen, while Chitosan triggers Induced Systemic Resistance (ISR) in the plant and enhances the production of phenolic compounds and defense enzymes, allowing the mixture to operate on multiple defensive levels simultaneously. Physiologically, chlorophyll content increased from 35.2 to 48.6 SPAD units in the T8 treatment (a 38.1% increase). Additionally, enzyme activities increased significantly compared to the control: POD by 340%, PPO by 280%, and CAT by 210%. This indicates that the mixture's mechanism of action is not limited to a direct effect on the pathogen but also includes the fortification of the plant's endogenous defense responses.

The study recommended the application of treatment T7 (Trichoderma + 1.0% Chitosan) in commercial fields due to its high efficacy and relatively lower cost compared to the highest concentration. It emphasized the necessity of conducting broader field studies under various environmental conditions, geographical regions, and seasons to ensure the stability of its efficacy. Furthermore, it recommended studying the long-term impact of the mixture on the soil and other beneficial organisms, evaluating its compatibility with pesticides and other elicitors used in Integrated Pest Management (IPM) programs, transferring this technology to farmers through agricultural extension and training programs, and investigating its efficacy against other fungal diseases affecting wheat (such as rust and blight) as well as other crops.