In vitro Evaluation of Nutrient-enriched Trichoderma harzianum Culture Filtrate against Alternaria solani Causing Early Blight of Tomato

Abstract

The necrotrophic fungus Alternaria solani causes early blight in tomato (Lycopersicon esculentum L.), a major disease of tomato crops worldwide that is associated with losses of 20 to 86 per cent in different regions. As the world's second-largest vegetable producer, India relies economically on crops such as tomato, making effective and environmentally friendly disease management important. Biological control using T. harzianum provides a more sustainable alternative to chemical fungicides. This investigation used the poisoned food technique under in vitro conditions to assess how culture filtrate prepared from a nutrient-enriched T. harzianum-based consortium affected the radial mycelial growth of A. solani. Thirteen treatments were examined: an untreated control and culture filtrates supplemented with calcium chloride, boric acid, phosphoric acid, potash phosphite, anhydrous ferric chloride or urea, each at 1 g and 2 g per 100 ml of PDB. Radial growth of A. solani was assessed on the 3rd and 6th days after inoculation (DAI), and inhibition relative to the control was calculated. At the 3rd DAI, inhibition across treatments varied from 26.14 to 45.45 per cent, with a comparable pattern at the 6th DAI. The greatest inhibition (45.45%) at both observation intervals was associated with T2, the culture filtrate containing 2 g calcium chloride; the next most effective treatments contained 2 g potassium dihydrogen phosphate (T6) and 2 g ferric chloride (T8). By contrast, T11 and T12, which contained urea, produced the weakest inhibition. The findings indicate the importance of calcium in maintaining fungal cell-wall integrity and membrane function. They also suggest that adding phosphorus to the fungal growth medium can favour antagonist growth and secondary-metabolite production, thereby contributing to suppression of the pathogen. Enriching T. harzianum-based culture filtrates with minerals, particularly calcium chloride, may offer an economical, environmentally friendly means of improving biological control of A. solani; further assessment under in vivo conditions is warranted.