Effects of olive mill wastewater, farmyard manure, and trichoderma harzianum on the growth of pepper (capsicum annuum L.) and on verticillium dahliae kleb.

This study was conducted to investigate the effectiveness of environmentally sustainable, biological, and organic control strategies against Verticillium wilt disease caused by Verticillium dahliae in pepper (Capsicum annuum L.) plants. Aiming to utilize agricultural waste and reduce chemical inputs, this research employed olive mill wastewater (OMW) derived from olive oil production, the biocontrol agent Trichoderma harzianum (T), and organic farmyard manure (FYM) (G), both individually and in combination.The experiments were carried out under both in vitro and in vivo conditions, evaluating disease severity, germination rate, plant morphology, physiological characteristics, and soil parameters. In in vitro trials, high concentrations of olive mill wastewater exhibited phytotoxic effects on pepper seeds, whereas a 1% concentration did not inhibit germination. Furthermore, T. harzianum significantly suppressed V. dahliae growth on PDA medium. Under in vivo conditions, especially in the combined applications of T, G, and OMW, significant improvements in pepper growth and notable reductions in disease severity were observed. The T+G and OMW+T+G treatments yielded statistically the highest values in growth parameters such as leaf number, stem diameter, and fresh-dry biomass. Particularly, the OMW+T+G+V treatment showed positive effects even under pathogen pressure. Therefore, this study demonstrates that agricultural waste and biological agents can be successfully integrated into sustainable production systems through integrated pest management approaches.