Effective control of Fusarium wilt on tomatoes using a combination of phenolic-rich plant extracts

Phenolic compounds occur in plants as secondary metabolites with potent biological activity to control pathogens. Tomato is the world’s second most cultivated vegetable but suffers attack by Fusarium oxysporum, causing Fusarium wilt disease that severely impacts crop yield and quality. This study focused on four phenolic-rich plant extracts and their mixtures to control F. oxysporum in vitro and in tomatoes. The highest phenolic sources were Eucalyptus camaldulensis, Chromolaena odorata, Bidens pilosa, and Azadirachta indica with superior phenolic contents ranging from 33.49 to 95.29 mg GAE/g. Crucial phenolic compounds identified in the plant samples included gallic acid (36.37 – 152.75 mg/100 g), chlorogenic acid (45.15 – 503.21 mg/100 g), and rutin (24.23 – 323.44 mg/100 g). The in vitro antifungal activity of the plant extracts correlated well with their total phenolic contents. The extract combination exhibited a synergistic effect on F. oxysporum with inhibitoty activity at 9.3, 5.5, 4.6 and 3.0 folds higher than the individual extracts of A. indica, B. pilosa, E. camaldulensis, and C. odorata, respectively. At the greenhouse scale, preventive and curative treatment using the phenolic-rich extract mixture significantly reduced the disease index by 26.7% and 28.0%, respectively at day 28 after fungal infection. Preventive treatment gave the best control efficacy of 61.27% at day 14 that was comparable to the chemical fungicide Ridomil Gold. Additionally, the application of the combined extract significantly improved the tomato growth parameters such as height and stem diameter. Results demonstrated that use of crude plant extracts rich in polyphenols was an effective, economical, and practical approach to manage crop pathogens on a large scale.