In vitro evaluation of bioagents and their consortia against Sclerotium rolfsii causing collar rot of chickpea

Introduction

Growing awareness of residue free produce and environmental safety has made chemical free plant health management a major challenge for present day agriculture. Antagonistic microorganisms and other biological technologies are therefore receiving greater attention in crop protection (Sulaiman et al., 2024) [1] . The biocontrol agents colonize the rhizosphere and leave behind no hazardous residues (Tewari et al., 2001) [2] . Most biocontrol strategies, however, have been built around a single antagonist directed against a single pathogen which partly accounts for their variable performance under field conditions (Rajasekhar et al., 2016) [3] . A single bioagent can rarely be expected to perform uniformly across soil types and against all phytopathogens (Nandakumar et al., 2001) [4] . Consequently, microbial consortia, defined as two or more microbial groups that interact synergistically and act together as a community, are being favoured over single bioinoculants for crop protection, since single strains of diverse microorganisms are generally less effective than consortia (Sudharani et al., 2014) [5] . Among the soil borne diseases of chickpea, collar rot caused by Sclerotium rolfsii (teleomorph-Athelia rolfsii) ranks among the most damaging alongside Fusarium oxysporum f. sp. ciceris and Rhizoctonia bataticola and is responsible for yield losses that range 60 -70 per cent when conditions favour the pathogen (Patra et al., 2023) [6] . The pathogen is remarkably polyphagous attacking more than 500 plant species and persists in soil and crop debris as sclerotia that remain viable for several years making it exceptionally difficult to eradicate once established in a field (Chowdary et al., 2024) [7] . Infection at the collar region is accompanied by profuse white silky mycelium and mustard like sclerotia resulting in pre and post emergence seedling mortality and appreciable plant stand loss. The prolonged survival of sclerotia, the saprophytic ability of the fungus and the limited reach of foliar fungicides at the collar region together make chemical management of this disease inadequate. In recent years, therefore, increasing emphasis has been placed on the combined use of biocontrol agents possessing different mechanisms of action, so as to improve the level of disease suppression and overcome the inconsistency of single bioagents (Thakkar et al., 2015) [8] . This approach has recently found field level support with integrated application of Trichoderma alongside soil amendments substantially lowered collar rot incidence in chickpea under natural field conditions (Paveen et al., 2025) [9] , reinforcing the case for consortium and integrated strategies over reliance on any single biocontrol component. In view of the potential benefits of microbial consortia, the present investigation was undertaken to evaluate selected fungal and bacterial bioagents, alone and in compatible combinations against S. rolfsii under In vitro conditions.

Material and methods

The laboratory study was conducted in the Department of Plant Pathology, College of Agriculture, Raichur University of Agricultural Sciences, Raichur during 2025-26. The biocontrol agents viz., Trichoderma asperellum UASR strain, Bacillus subtilis SE76, Streptomyces nenu DS-11 and Pseudomonas fluorescens UASR strain used for the studies were collected from Biocontrol Laboratory, Department of Plant Pathology, College of Agriculture, Raichur. The Sclerotium rolfsii was isolated from chickpea plants showing typical collar rot symptoms and maintained on potato dextrose agar (PDA) at 27 ± 2 °C. The bio-efficacy of the fungal and bacterial biocontrol agents was evaluated under In vitro conditions against S. rolfsii using the dual culture technique (Dennis et al., 1971) [10] . The 20 ml of sterilized and cooled PDA were poured into sterile Petri plates and allowed to solidify. For evaluation of the fungal biocontrol agent, a 5 mm mycelial disc of S. rolfsii was placed at one end of the plate and the antagonist at the opposite end. For bacterial and actinomycete antagonists, a 5 mm pathogen disc was placed on one side and the antagonist was streaked or spread on the opposite side. For testing combinations of compatible bioagents, a 5 mm pathogen disc was placed at the centre of the PDA plate and the compatible bioagents were placed or streaked on either side of the pathogen at equal distances. Three replications were maintained for each treatment along with a control containing only the test fungus. Plates were incubated at 27 ± 1 °C and the radial growth of the pathogen in dual culture and control plates was measured when the pathogen in the control plates had fully covered the medium. Percent inhibition of mycelial growth was calculated using the formula given by Vincent (1927) [11] .

𝐼 = C-T 𝐶 × 100

Where, I = percent inhibition of mycelial growth, T = radial growth of pathogen in treatment (cm), C = radial growth of pathogen in control (cm).

Results

All the biocontrol agents either alone or in combination significantly inhibited the mycelial growth of Sclerotium rolfsii under In vitro conditions (Table 1, Fig. 1 and Plate 1). The antagonistic activity of the fungal and bacterial bioagents was higher in consortia than when the agents were applied individually. Among the individual antagonists, Trichoderma asperellum (T 1 ) recorded the maximum inhibition of S. rolfsii (61.00 %) and was statistically superior to all other single treatments. It was followed by Streptomyces nenu (T 3 ) with 28.88 per cent inhibition and Bacillus subtilis (T 2 ) with 23.88 per cent inhibition. The least inhibition among the individual treatments was recorded in Pseudomonas fluorescens (T 4 ) with 23.00 per cent which was statistically on par with T 2 . Compared with the bacterial antagonists, the fungal antagonist showed a markedly higher level of suppression of the pathogen. Among the two agent combinations,

Conclusion

Fungal and bacterial bioagents, alone and in combination were found effective against Sclerotium rolfsii under In vitro conditions. The microbial consortium comprising Trichoderma asperellum + Bacillus subtilis + Streptomyces nenu + Pseudomonas fluorescens (T 15 ) was the most promising bioagent treatment inhibiting mycelial growth of the pathogen by 73.33 per cent. Microbial consortia can therefore be explored for the successful management of soil borne plant pathogens such as S. rolfsii in chickpea.

Acknowledgement

AcknowledgementI would like to express my sincere gratitude to the Department of Plant Pathology, University of Agricultural Sciences, Raichur, Karnataka, India for supporting and facilitating the study.

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21. How to cite this article: Sankethreddy S, Gowdar S, Amaresh Y, Yenjerappa S, Arunkumar H. In vitro evaluation of bioagents and their consortia against Sclerotium rolfsii causing collar rot of chickpea. International Journal of Advanced Biochemistry Research. 2026;10(9):867-870. doi: https://www.doi.org/10.3354