In vitro bio efficacy of biocontrol agents against Colletotrichum truncatum associated with leaf blight disease of Linseed in India
Abstract
Leaf blight caused by Colletotrichum truncatum is an important fungal disease of linseed (Linum usitatissimum L.) that can reduce crop growth and productivity. Considering the ecological concerns associated with excessive fungicide use, the present study evaluated the in vitro efficacy of Trichoderma asperellum and Pseudomonas fluorescens against C. truncatum using the dual culture technique. Among T. asperellum treatments, T₁ showed the greatest antagonistic activity, restricting pathogen growth to 25.40 ± 0.52 mm with 70.80% inhibition, followed by T₂ (26.80 ± 0.63 mm; 69.20%) and T₃ (27.65 ± 0.58 mm; 68.22%), compared with 87.00 ± 0.00 mm in the control. Among P. fluorescens treatments, T₂ was most effective, limiting mycelial growth to 29.10 ± 0.56 mm and achieving 66.65% inhibition, followed by T₁ (31.25 ± 0.78 mm; 64.18%) and T₃ (32.53 ± 0.75 mm; 62.72%), against 87.25 ± 0.73 mm in the control. Overall, T. asperellum exhibited superior antagonistic activity. This study demonstrates that promising biocontrol agents identified through in vitro screening could serve as environmentally compatible components of an integrated disease management strategy for the management of C. truncatum-induced leaf blight in linseed.
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Introduction
Linseed (Linum usitatissimum L.), commonly known as flaxseed, is an important traditional rabi oilseed crop cultivated during the winter season. Its significance is attributed to its high-quality seed oil, nutritional value, and industrial applications. The crop also serves as a valuable component of diversified cropping systems because of its adaptability to relatively poor soils and water-limited conditions. Linseed oil is widely used in the food, cosmetic, and eco-material industries owing to its desirable fatty acid composition and functional properties (Zanetti et al., 2013). Based on morphological characteristics and end use, the crop is broadly classified into two types: seed type (linseed), primarily cultivated for oil production and fibre type (flax), grown mainly for fibre production. In India, cultivated varieties are predominantly seed types and are grown primarily for oil extraction (Singh, 2016; Biradar et al., 2016).
Linseed seeds generally contain approximately 33–47% oil, depending on genotype, environmental conditions, and other factors. The oil is particularly valued for its high concentration of essential fatty acids and is an important plant-based source of omega-3 fatty acids, especially alpha-linolenic acid (ALA), which constitutes approximately 55% of the total fatty acids. In India, a substantial proportion of linseed oil is utilized for industrial purposes, including the manufacture of boiled, borated, epoxidized, aluminate, urethane, and isomerized oils (Mueed et al., 2022). During 2021–22, linseed was cultivated in India on approximately 2.0 lakh hectares, producing about 1.2 lakh metric tonnes, with an average productivity of 659 kg ha⁻¹. The crop is cultivated extensively in Madhya Pradesh, Rajasthan, Bihar, Uttar Pradesh, Assam, Jharkhand, and several other states. Madhya Pradesh accounts for the largest area under cultivation, with approximately 1.16 lakh hectares and a production of about 0.55 lakh tonnes, although its productivity remains relatively low at approximately 474 kg ha⁻¹ (APEDA, 2022).
Despite its economic and nutritional importance, linseed production is affected by several biotic constraints, particularly fungal diseases that reduce plant growth, yield, and seed quality (Patel et al., 2023). Leaf blight is an important disease that reduces photosynthetic area and may cause premature defoliation and yield loss. Colletotrichum truncatum is an important fungal pathogen causing necrotic leaf lesions that may enlarge and coalesce under warm and humid conditions. Its survival in infected crop residues can contribute to disease persistence and subsequent outbreaks (Sampathkumar et al., 2025). A distinct leaf blight caused by Colletotrichum truncatum was recently observed in linseed fields of Karnataka, and this pathogen–disease association is newly reported in India (Sampathkumar et al., 2025).
Conclusion
This study confirms the in vitro efficacy of Trichoderma asperellum and Pseudomonas fluorescens against Colletotrichum truncatum, the causal agent of leaf blight in linseed. Among the tested biocontrol agents, T. asperellum (T₁) exhibited the highest antagonistic activity, restricting pathogen growth to 25.40 ± 0.52 mm with 70.80% inhibition, followed by P. fluorescens (T₂), which limited mycelial growth to 29.10 ± 0.56 mm with 66.65% inhibition. Both biocontrol agents significantly suppressed the mycelial growth of the pathogen compared to untreated controls.
The study provides baseline information for the biological management of linseed leaf blight caused by C. truncatum, a newly reported pathogen–disease association in India. The promising results obtained from in vitro screening warrant further evaluation of the most effective isolates under greenhouse and field conditions. Integration of these biocontrol agents into sustainable disease management strategies could reduce dependence on synthetic fungicides and contribute to environmentally friendly linseed production.
• Limitations of the Study: This study was conducted under controlled in vitro conditions, and the efficacy of the biocontrol agents may vary under field conditions due to environmental factors, microbial competition, and other variables. The mechanisms of antagonism were not specifically investigated, and pathogenicity testing was not performed in this study (though the pathogen identity was confirmed molecularly in earlier work). Future research should focus on evaluating the selected biocontrol agents under greenhouse and field conditions and investigating their mechanisms of action.
• Future Research Directions: Future studies should include (i) evaluation of the most effective isolates under pot and field conditions, (ii) investigation of the mechanisms of antagonism (e.g., production of volatile compounds, chitinase activity, siderophore production), (iii) compatibility testing with other disease management practices, (iv) formulation and application optimization, and (v) assessment of the impact of biocontrol agents on crop growth and yield.
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