Antagonistic potential of Trichoderma harzianum and Azadirachta indica against Fusarium oxysporum f. sp. capsici for the management of chilli wilt

Fusarium oxysporum f. sp. capsici (Foc) induces wilt disease in chilli and affects its yield. Implementing microorganisms and plant extracts for plant disease management has recently gained momentum as chemical measures pose a serious threat to the environment. Field experiments were conducted over two consecutive years to evaluate the effectiveness of Trichoderma harzianum (either as seed treatment or as soil application) and neem (Azadirachta indica; as seed treatment with leaf extract) alone or in combination, in managing chilli wilt. Untreated plots served as control. Chilli plants were grown in field plots of 2 × 2 m2 size, and experiments were organised in complete randomised block design with three replications. In the absence of Foc, T. harzianum (sa) + A. indica (st) increased growth and yield of chilli. In Foc-inoculated plots, both, T. harzianum and A. indica, showed a reduction in disease severity. Disease severity and chlorophyll content were negatively correlated (P ≤ 0.05). During both years, T. harzianum (sa) + A. indica (st) caused the strongest reduction in wilt severity and the highest increase in chlorophyll content, number of fruit/plant, fresh yield/plant, fresh and dry weight as well as plant length. Soil population of T. harzianum increased significantly during crop growth and was higher in plots inoculated with the pathogen. Highest concentrations (4.52 × 104 and 4.87 × 104 cfu/g soil) were found in plot soil where T. harzianum was applied in the soil, whilst maximum increase of Foc (3.02 × 104 and 3.05 × 104 cfu/g soil) was observed in plots that lacked any treatment.