In vitro antifungal activity of cassia fistula leaf extracts against major phytopathogenic fungi

Introduction

Fungal plant pathogens represent a major constraint to global agricultural productivity, causing extensive yield and quality losses. Species of Alternaria, Cercospora, Colletotrichum, and Fusarium are widely distributed and responsible for destructive foliar diseases, blights, anthracnose, and wilts in numerous crops [1][2][3] . Although chemical fungicides remain the primary control strategy, their prolonged use has resulted in resistance development, environmental contamination, and negative impacts on non-target organisms [4,5] . The search for sustainable alternatives has intensified interest in plant-derived antifungal agents. Botanical extracts are biodegradable, generally less toxic, and often exhibit multi-target modes of action, reducing the likelihood of resistance [6][7][8] . Several medicinal plants traditionally used for treating microbial infections have demonstrated promising antifungal activity against plant pathogens [6,9] . Cassia fistula L. (Fabaceae) is a widely distributed medicinal plant with reported antimicrobial properties [10,11] . However, systematic evaluation of its antifungal efficacy against major phytopathogenic fungi relevant to agriculture remains limited. The present study therefore aimed to evaluate the in vitro antifungal activity of aqueous, methanolic, and acetone extracts of C. fistula leaves against four important phytopathogenic fungi, with emphasis on solventdependent efficacy, concentration response, and incubation time effects.

Materials and Methods

Preparation of leaf extracts:

Fresh leaves of Cassia fistula were collected, shade-dried, and powdered. Aqueous, methanolic, and acetone extracts were prepared separately. Organic solvent extractions were performed using Soxhlet apparatus, while aqueous extraction was carried out by maceration. Concentrated extracts were dried and stored at 4 °C until use.

Fungal pathogens:

Pure cultures of Alternaria spp., Cercospora spp., Colletotrichum spp., and Fusarium spp. were isolated from infected plant tissues and maintained on potato dextrose agar (PDA). Pathogens were identified based on colony morphology and microscopic characteristics.

Antifungal assay:

Antifungal activity was evaluated using the poisoned food technique. Extracts were incorporated into molten PDA at different concentrations and poured into Petri plates. Control plates contained PDA without extract. Mycelial discs were placed centrally, and plates were incubated at 25±2 °C. Radial mycelial growth was measured at 3 and 5 days after inoculation (DAI). Percentage inhibition was calculated relative to control.

Plate 1: Pure cultures of phytopathogens, Alternaria, Cercospora, Colletotrichum and Fusarium

Statistical analysis:

Experiments were conducted in triplicate. Data were analyzed using ANOVA, and treatment means were compared at p < 0.05.

Results

All Cassia fistula leaf extracts significantly inhibited mycelial growth of the tested fungi compared to control.

Antifungal activity varied with solvent, concentration, fungal species, and incubation period. Observed data of Alternaria, Cercospora, Colletotrichum and Fusarium, respectively, are presented in Plates 2-5. Mean diameters of colonial growth and percentage inhibition and corresponding ANOVA are presented in Tables 12345678. Methanolic extract consistently exhibited the highest antifungal activity against all fungi, followed by acetone extract, while aqueous extract showed comparatively lower inhibition. Inhibition increased with extract concentration and was generally higher at 5 DAI than at 3 DAI. Among the fungi tested, Alternaria and Cercospora were more susceptible to extract treatment, whereas Fusarium exhibited relatively lower sensitivity.

Discussion

The present study demonstrates clear in vitro antifungal activity of Cassia fistula leaf extracts against major phytopathogenic fungi. The superior efficacy of methanolic and acetone extracts compared to aqueous extract suggests that solvent selection plays a critical role in extracting antifungal constituents, consistent with previous reports on botanical antifungal agents [6,12] . The observed concentration-and time-dependent inhibition indicates sustained antifungal activity during incubation. Differential sensitivity among fungal species may be attributed to variations in cell wall composition, membrane permeability, and physiological responses [1,2] . The relatively lower susceptibility of Fusarium aligns with earlier findings reporting higher tolerance of this genus to plant-derived antifungal compounds [8,13] .

Although the study was limited to in vitro assays using crude extracts, the consistent inhibitory patterns observed across multiple fungi highlight the potential of C. fistula leaves as a source of botanical antifungal agents.

Conclusions

Cassia fistula leaf extracts exhibit significant in vitro antifungal activity against Alternaria, Cercospora, Colletotrichum, and Fusarium. Methanolic extract was the most effective, followed by acetone, while aqueous extract showed lower activity. Antifungal effects were concentration-dependent and increased with incubation time. These findings support further investigation of C. fistula leaf extracts for development of botanical fungicides aimed at sustainable management of fungal plant diseases.

References

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