Vitro Evaluation of the Inhibitory Effects of Neem (Azadirachta indica) Leaf Extract and Salicylic Acid on the Mycelial Growth of Tomato Rot Fungi and Phytochemical Analysis of Neem Leaf Extract

This study evaluated the in vitro inhibitory effects of neem (Azadirachta indica) leaf extract and salicylic acid on the mycelial growth of fungi associated with tomato rot and determined the phytochemical constituents of neem leaf extract. Fungi were isolated from rotten tomato fruits, and their occurrence and pathogenicity were assessed. The antifungal activities of different concentrations of neem leaf extract and salicylic acid were evaluated using the pour plate method, while phytochemical constituents were identified through qualitative screening procedures. Four fungal species were isolated: Colletotrichum gloeosporioides (37.78%), Aspergillus niger (25.75%), Botryoploida theobromae (18.61%) and Penicillium digitatum (17.86%). The reported pathogenicity results showed that all four isolates caused decay in inoculated tomato fruits. The inhibitory effects of neem leaf extract and salicylic acid increased with concentration and incubation time. On Day 6, 30% neem leaf extract produced 78.72% inhibition, while 30 g/L salicylic acid produced 77.41% inhibition of C. gloeosporioides. The combination of 30% neem leaf extract and 30 g/L salicylic acid produced the highest reported inhibition of 84.15%. Phytochemical screening indicated high concentrations of alkaloids, cardiac glycosides, glycosides, flavonoids and terpenoids, while steroids, saponins, tannins, triterpenes, phytosterols and phenols were moderately present. Anthraquinones, anthocyanins, phlobatannins and amino acids were reported absent. The findings suggest that neem leaf extract and salicylic acid have potential as treatments for suppressing tomato rot fungi under in vitro conditions. Further studies are required to validate their effectiveness, safety and practical application under postharvest storage conditions.