Integrated effects of Curcumin application methods and Trichoderma afroharzianum on Fusarium wilt management and biochemical responses in hot pepper (Capsicum annuum)

Fusarium wilt caused by Fusarium oxysporum is one of the major diseases threatening hot pepper, Capsicum annuum, and results in devastating losses. Some plant extracts such as curcumin and turmeric extracts have shown in vitro efficacy against Fusarium. These extracts possess broad-spectrum antifungal activity against a number of plant pathogens such as Fusarium sp, Alternaria sp, and Botrytis sp. Curcumin is also known for its safety and low toxicity in plants. Increasing concentrations of Curcumin progressively inhibited radial fungal growth, reaching a maximum inhibition of 62.2% at 3.0%. In addition, the highest increase in plant growth was recorded with a foliar application of Curcumin in combination with the bio-control agent Trichoderma afroharzianum (BCA) concerning the height of the plants and length of roots, the weight of fruit, and also the suppression of disease severity, indicating significant benefits with integrated application approaches. With this, significantly higher concentrations of growth hormones Gibberellic acid (GA3), antioxidant enzymes (Catalase CAT and Peroxidase POD), and micronutrients (Cu, Fe, Zn, B) were found in leaves, while flood (land water addition) treatments tended to have higher Abscisic acid (ABA) levels and enzyme activities related to stress responses. The concentration of secondary metabolites, including capsaicin and total carbohydrates, were higher with combined foliar and BCA treatments over flood application alone, together with an increase in macronutrient uptake (N, P, K, Ca, and Mg). Results suggest that the combination of Curcumin with T. afroharzianum is a non-toxic, effective, and environmentally friendly approach for the control of Fusarium wilt along with improving growth and enhancing biochemical and nutritional potentiality in hot pepper plants. In contrast, flood application of Curcumin showed less or no effect on most of the parameters, which underlines the importance of the mode of application to achieve maximum efficacy.