Bioefficacy of Selected Botanicals against Xanthomonas-Induced Bacterial Spot in Solanum lycopersicum L.

Abstract

Tomato bacterial spot, caused by Xanthomonas vesicatoria, is a destructive disease that reduces yield and quality. In this study, leaf extracts of Psidium guajava, Azadirachta indica, Ricinus communis, and Lantana camara were evaluated for antimicrobial activity at concentrations ranging from 25–100 ug/ml. The assays revealed dose-dependent inhibition, with P. guajava showing the strongest effect (zone of inhibition up to 22 mm, 86.3% growth suppression at 100 ug/ml). A. indica exhibited moderate activity (15 mm, 68.1%), while R. communis showed steady inhibition (12 mm, 54.5%). L. camara was inactive at lower concentrations but achieved 11.5 mm and 51.1% inhibition at 100 ug/ml. phytochemical profiling indicated that tannins, terpenoids, saponins, and anthraquinones contribute to the observed antimicrobial potency. These findings highlight Psidium guajava leaves extract as the most promising bio-control candidate, with Neem, Castor, and Lantana serving as complementary agents. Collectively, plant-derived phytochemicals offer sustainable alternatives to copper-based bactericides, combining direct pathogen suppression with host defence induction.

Introduction

Tomato is a major global vegetable crop, but its yield is heavily affected by bacterial diseases, especially bacterial leaf spot caused by Xanthomonas species. Heavy reliance on chemical pesticides has led to environmental damage, health risks, and increasing pathogen resistance, creating a need for eco-friendly alternatives. Plant-based biopesticides are therefore explored as sustainable disease management options.

The study focuses on using leaf extracts from medicinal plants (Psidium guajava, Azadirachta indica, Lantana camara, and Ricinus communis) to control tomato bacterial spot. These plants contain bioactive compounds such as alkaloids, phenols, flavonoids, terpenoids, tannins, and saponins, which contribute to antimicrobial activity.

Plant extracts were prepared using aqueous extraction methods and tested in vitro against Xanthomonas vesicatoria. Phytochemical screening confirmed the presence of multiple antimicrobial compounds, with each plant showing a distinct chemical profile. Antibacterial assays showed all extracts inhibited bacterial growth, but effectiveness varied.

Guava (P. guajava) showed the highest antibacterial activity (up to ~86% inhibition), followed by Neem (A. indica) with moderate effectiveness (~68%). Castor (R. communis) and Lantana (L. camara) showed weaker but dose-dependent inhibition.

Conclusion

The antimicrobial assays confirmed that leaf extracts of Psidium guajava, Azadirachta indica, Ricinus communis, and Lantana camara inhibited the growth of Xanthomonas vesicatoria, though with varying potency. P. guajava exhibited the strongest activity, establishing it as a promising biocontrol candidate, while neem provided moderate suppression. Castor and lantana, though less potent, may serve as complementary agents in synergistic formulations. Phytochemical profiling supports these findings, with guava and neem enriched in tannins and terpenoids that can suppress the pathogen and enhance host defense responses, while lantana and castor contribute saponin- and anthraquinone-mediated antimicrobial effects. Collectively, these findings highlight the potential of plant-derived phytochemicals as sustainable alternatives to copper-based bactericides, offering both direct pathogen inhibition and host defence induction, thereby aligning with eco-friendly agricultural practices.

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Copyright

Copyright © 2026 Kadam Sakshi S., Takur Divya S., Tambe Harshad S., Kakad Subhash L.. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.