Efficacy of plant extracts on biocontrol of Phytophthora infestans (Mont.) de bary infestation in Solanum lycopersicum L.

Tomato is one of the most widely cultivated vegetables worldwide and plays an essential role in food security, income generation, and rural employment. Production of tomato is threatened by late blight disease caused by Phytophthora infestans. Botanical extract of Ocimum gratissimum, Carica papaya, Vernonia amygdalina, and Syzygium aromaticum were reported to have antifungal potential under laboratory and greenhouse conditions. The study investigated the effectiveness of Syzygium aromaticum and Ocimum tenuiflorum as natural alternatives for managing the disease. Laboratory and greenhouse experiments were conducted at the Department of Plant Science and Biotechnology, Bayero University Kano. Botanical extract of Syzygium aromaticum and Ocimum tenuiflorum were prepared at 2.5, 5.0, 7.5 ml⁻¹ while distilled water was used as the control. The greenhouse experiment was laid out as a 2 × 3 × 3 factorial with three replicates in a completely randomized design and tested the antifungal properties of the plant extracts using different solvents (aqueous, ethyl acetate and acetone). The results showed that each plant extract significantly (p < 0.05) inhibited the growth of P. infestans in a concentration-dependent pattern with higher inhibition (100%) of P. infestans observed in S. aromaticum and O. tenuiflorum extracted with acetone and ethyl acetate as solvents. Leaf area reduced from 58.27% to 71.87% from lower to higher concentrations compared to negative treatment. In particular, the extracts of clove and holy basil at higher concentrations showed strong performance in reducing disease symptoms and improving plant growth (leaf area, biomass, number of leaves and chlorophyll content). Gas chromatography–mass spectrometry analysis of S. aromaticum extract identified phytochemicals eugenol, luteolin, and quercetin known for their antifungal properties. These findings highlight the potential of using botanical extracts as eco-friendly and sustainable alternative to synthetic fungicides in tomato late blight disease. A field trial using ethyl acetate extract of S. aromaticum is worthy.