Exploring eco-friendly plant extracts for the management of pigeonpea wilt caused by Fusarium udum

Introduction

Pigeonpea (Cajanus cajan (L.) Millspaugh), is an important pulse crop valued for its high nutritional content. The crop contains about 21% protein, with the embryo contributing nearly 50% of the total protein content. In addition, its good source of water-soluble vitamins including thiamine, riboflavin, and niacin, and is particularly notable for its high vitamin C content (56.9 mg per 100 g), making it one of the richest sources of this vitamin (Ellong et al., 2015) [3] . Its ranks as the second most important pulse crop in India after green gram, and the country is the largest producer worldwide. Globally, the crop is cultivated over 63.57 lakh hectares with a production of 54.75 lakh tonnes and an average productivity of 861.25 kg ha⁻¹. In India, pigeonpea occupies about 5.05 million hectares with a production of approximately 4.34 million tonnes and an average yield of 859 kg ha⁻¹ (Anonymous, 2024). Its susceptible to infection by more than 200 pathogens reported across 23 countries worldwide (Nene et al., 1982) [7] . In India, Fusarium wilt poses one of the most serious constraints to pigeonpea production, particularly in major growing states such as Uttar Pradesh, Madhya Pradesh, Bihar, and Maharashtra. The disease is widespread across all pigeonpea-growing regions of the country and is responsible for substantial yield losses ranging from 30 to 100% (Biswas and Ghosh, 2016) [1] . Although wilt symptoms may appear at the seedling stage, the maximum plant mortality generally occurs during the flowering and pod formation stages. Fusarium udum, the causal organism, is a host-specific, soil-borne facultative parasite that invades the plant through fine roots and subsequently colonizes various plant tissues (Khune, 1990) [6] . Frequent fungicide use harms beneficial soil microorganisms that are not the intended targets, leading to environmental risks such as soil and water pollution (Zhou et al., 2023) [13] . In discriminate use of these chemicals has led to development of fungicide resistance strain (Okigbo, 2004) [8] . Plant extracts and bioagents are emerging as eco-friendly way to manage pathogen. So, the objective of this investigation was to evaluate the potential of plant extracts, bioagents and fungicides against Fusarium udum.

Materials and Methods

Study site and Isolation

Pigeonpea plants showing typical symptoms of Fusarium wilt were collected from the experimental fields of Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur, The experimental soil consisted of medium-black Vertisols with uniform texture, moderate NPK fertility, and good drainage. Small tissue segments (1-2 mm) from the advancing margins of infected tissues were washed, surface sterilized with 0.1% mercuric chloride for 30s, rinsed thrice with sterile distilled water, and aseptically transferred onto potato dextrose agar (PDA). The cultures were incubated at 28±1 °C, and actively growing hyphal tips were subcultured after 72 h to obtain pure cultures. The pathogen was maintained on PDA by periodic subculturing and stored at 5±1 °C for long-term preservation.

Estimation of Spore Formation of Fusarium udum

Sporulation was assessed at the end of the incubation period by excising a 5 mm mycelial disc from the culture and suspending it in 10 ml of sterile distilled water. The suspension was shaken thoroughly to release the spores, and spore counts were determined using a haemocytometer. Sporulation was graded as excellent, good, fair, poor, or nil based on the scale described by Vani et al. (2019) [12] .

Efficacy of plant extract against Fusarium wilt

The experiment involved testing the antifungal efficacy of various Plant Extracts at three different concentrations 5%, 10%, and 15%. Seven commonly available plant species Parthenium, Neem, Jatropha, Lantana, Ashwagandha, Tobacco, and Ginger were assessed for their antifungal properties against Fusarium udam. Extracts were prepared from plant parts such as leaves and rhizomes, following the standard method described by Gerard et al. (1994). Fresh plant materials were first washed with tap water, then rinsed with sterile distilled water. These parts were ground with sterile distilled water in a 1:1 (v/w) ratio using a pestle and mortar. The resulting mixture was filtered through doublelayered cheesecloth to obtain a clear plant extract solution.

The concentrated phytoextracts were passed through bacteria-proof filters (typically 0.2 µm pore size membrane filters made of cellulose acetate or PVDF) under sterile conditions. All filtration procedures were performed inside a laminar airflow chamber to maintain aseptic conditions. The sterilized extracts were collected in sterile glass vials, sealed, and labelled appropriately for further anti-microbial testing.

Stock solutions of plant extracts at 5, 10, and 15% concentrations were prepared by mixing 95, 90, and 85 ml of sterilized potato dextrose agar (PDA), respectively. The antifungal efficacy of the botanicals against Fusarium udum was evaluated using the poison food technique at these three concentrations. The experiment consisted of seven treatments with three replications each. A 5 mm mycelial disc taken from a 7-day-old culture of F. udum was aseptically placed at the center of PDA plates amended with plant extracts, while PDA plates without extracts served as the control. All plates were incubated at 28±1 °C, and radial growth of the fungus was recorded after 144 hours. The observed mycelial growth data were subsequently used to calculate the percentage inhibition of fungal growth using the standard formula.

Results and Discussion Efficacy of plant extract

Seven commonly available plant species Parthenium, Neem, Jatropha, Lantana, Ashwagandha, Tobacco, and Ginger were tested at a 15% concentration against Fusarium udum using the poisoned food technique on Potato Dextrose Agar (PDA) medium. Among all at 15% concentration Ashwagandha recorded the highest percent growth inhibition (57.25%) of the pathogen, indicating the most effective suppression. Its having some antifungal properties like Withanolid essteroidal lactones which inhibit spore germination, Flavonoids which suppress fungal enzyme Somniferin which inhibit fungal DNA, protein synthesis and reduce metabolic activity. In contrast, Tobacco showed the least inhibition (39.46%). 0thers are like Neem (51.47%), Parthenium (49.46%), and Lantana (45.47%). These extracts significantly suppressed fungal growth compared to the untreated control (87.00 mm). Ginger and Tobacco also displayed moderate inhibition of 44.69% and 39.46%, respectively. The present study was in agreement with the report of Daradka et al. (2021) [2] who also reported that the antifungal activity of 10 plant extracts against F. oxysporum associated with tomato diseases using disc-diffusion methods they found that due to the presence of alkaloids, flavonoids, tannins, and terpenoids that disrupt fungal cell functions and supress the fungal growth. Singh et al. (2017) [11] also tested 12 botanicals at various concentrations. Both garlic oil and neem oil (Nemazal) at 10% completely suppressed F. oxysporum growth, followed by mustard oil (69.26%), Datura (46.67%), and Withania somnifera (34.44%). Gupta et al. (2015) [4] evaluated the antifungal activity of crude extracts from 20 plants using the "food poisoning method" against Fusarium oxysporum F. sp. udum, the causative agent of pigeon pea wilt. They found that the leaf extracts of Phyllanthus niruri and Vitex negundo exhibited the highest toxicity against the pathogen.

Conclusion

The present study clearly demonstrated that plant extracts possess varying degrees of antifungal activity against Fusarium udum. Among the seven botanicals evaluated, Ashwagandha proved to be the most effective, followed by Neem and Parthenium, showing significant inhibition of mycelial growth and reduction in sporulation under in vitro conditions. The antifungal efficacy increased with an increase in concentration, with 15% being the most effective dose. Tobacco and Jatropha were comparatively less effective. The inhibitory action of these botanicals may be attributed to the presence of bioactive compounds such as with anolides, flavonoids, and other secondary metabolites that interfere with fungal growth and metabolism. The findings suggest that selected plant extracts, especially Ashwagandha and Neem, can serve as promising ecofriendly alternatives to chemical fungicides and may be integrated into sustainable management strategies for Fusarium wilt of pigeonpea. However, further studies under field conditions are required to validate their effectiveness and practical applicability.

References

1. Biswas K, Ghosh P. Recent advancements and biological management of Fusarium udum: A causative agent of pigeon pea wilt. Int J Appl Nat Sci. 2016;5(3):57-72.
2. Daradka HM, Saleem A, Obaid WA. Antifungal effect of different plant extracts against phytopathogenic fungi Alternaria alternata and Fusarium oxysporum isolated from tomato plant. J Pharm Res Int. 2021;33(31A):188197.
3. Ellong EN, Billard C, Adene S, Rochefort K. Polyphenols, carotenoids, and vitamin C content in tropical fruits and vegetables and impact of processing methods. Food Nutr Sci. 2015;6:299-313.
4. Gupta AK, Chaudhary S, Samuel CO, Upadhyaya PP. Antifungal activity of some locally available plants against Fusarium oxysporum F. sp. udum. Int J Curr Microbiol Appl Sci. 2015;4(11):695-699.
5. Jaywant KS. Pathogenic variability and management of Fusarium wilt of chilli (Capsicum annuum L.) [PhD thesis]. Hisar (India): CCS Haryana Agricultural University; 2016.
6. Khune R. Biological control of soil borne plant pathogens. Indian J Mycol Plant Pathol. 1990;17:1-9.
7. Nene YL, Kannaiya J, Reddy MV. Pigeonpea diseases: resistance screening techniques. Information Bulletin No. 9. Patancheru (India): ICRISAT; 1982.
8. Okigbo RN. A review of botanical control methods for post-harvest yams (Dioscorea spp.) in storage in South Eastern Nigeria. KMITL Sci J. 2004;4(1):207-215.
9. Shafique S, Asif M, Shafique S. Management of Fusarium oxysporum F. sp. capsici by leaf extract of Eucalyptus citriodora. Pak J Bot. 2015;47(3):11771182.
10. Shukla A, Dwivedi SK. Bioefficacy of plant extracts against Fusarium species causing wilt in pulses. IOSR J Eng. 2012;2(1):136-144.
11. Singh, Kumar M, Kumar S, Kumar A, Mehta N. Inhibitory effect of botanicals on growth and sporulation of Fusarium oxysporum inciting wilt of chilli (Capsicum annuum L.). J Pharmacogn Phytochem. 2017;6(5):2199-2204.
12. Vani MS, Kumar S, Gulya R. In vitro evaluation of fungicides and plant extracts against Fusarium oxysporum causing wilt of mungbean. Pharma Innov J. 2019;8(8):297-302.
13. Zhou T, Guo T, Wang Y, Wang A, Zhang M. Carbendazim: ecological risks, toxicities, degradation pathways and potential risks to human health. Chemosphere. 2023;314:137723.