Integrated management of foot rot caused by Sclerotium rolfsii in finger millet using fungicides and bio-agents

Introduction

Finger millet (Eleusine coracana L.) is an important nutritious cereal crop cultivated predominantly in the semi-arid and tropical regions of Asia and Africa. It is valued for its remarkable adaptability to marginal environments, drought tolerance, high nutritional quality, and long storage life (Dida et al., 2008; Goron and Raizada, 2015) [6,7] . The crop is an excellent source of calcium, dietary fiber, iron, methionine, and essential amino acids, making it an important component of food and nutritional security, particularly in developing countries (Chandra et al., 2016; Gupta et al., 2017) [21,22] . In India, finger millet occupies a significant position among small millets due to its dual-purpose utility as food and fodder and its suitability under rainfed farming systems (Rao, 1980; Upadhyaya et al., 2006). Despite its resilience to adverse climatic conditions, finger millet is susceptible to several diseases caused by fungi, bacteria, and viruses. Among them, foot rot caused by Sclerotium rolfsii Sacc has emerged as an economically important disease in several finger milletgrowing regions (Pawar et al., 2013) [15] . The disease primarily affects the collar and basal stem region, causing rotting of tissues, chlorosis, wilting, lodging, and eventual death of infected plants. Under favorable environmental conditions such as high soil moisture, warm temperatures (25-35 °C), and dense crop canopy, the disease develops rapidly and can result in severe stand losses (Aycock, 1966; Punja, 1985) [1,17] . Sclerotium rolfsii is a destructive soil-borne basidiomycetous fungus with an exceptionally broad host range, infecting more than 500 plant species belonging to over 100 families (Aycock, 1966; Punja, 1985) [1,17] . The pathogen causes stem rot, collar rot, southern blight, and foot rot diseases in numerous economically important crops including groundnut, soybean, chickpea, pigeon pea, tomato, chilli, onion, potato, sunflower, wheat, barley, and finger millet (Mordue, 1974; Punja, 1985; Desai and Schlosser, 1999) [17,5] .

The pathogen survives in soil and plant debris through the formation of sclerotia, which serve as the primary source of inoculum. These sclerotia can remain viable in soil for several years and germinate under favorable conditions, making disease management difficult (Aycock, 1966; Chet and Henis, 1972) [23] . The disease cycle of S. rolfsii is strongly influenced by environmental factors. Warm temperatures, high relative humidity, and moist soil conditions favor mycelial growth, sclerotial germination, and disease development (Punja, 1985; Harlton et al., 1995) [17] . Furthermore, the pathogen exhibits considerable variability in cultural, morphological, pathogenic, and molecular characteristics among isolates from different hosts and geographical regions, which complicates management strategies (Okabe and Matsumoto, 2003; Sarma et al., 2002) [24,25] . In finger millet, foot rot has been reported to cause significant yield reductions by reducing plant stand and vigor. Pawar et al. (2013) [15] reported grain yield losses of up to 27.40 per cent and fodder yield losses of 23.31 per cent due to foot rot infection. Similar losses caused by S. rolfsii have been reported in several field and horticultural crops worldwide, highlighting the economic significance of the pathogen (Punja, 1985; Mahadevakumar et al., 2016) [26,27] . Management of foot rot remains challenging because of the soil-borne nature of the pathogen, prolonged survival of sclerotia, wide host range, and lack of resistant cultivars (Punja, 1985; Mahadevakumar et al., 2016) [17] . Cultural practices such as crop rotation, deep ploughing, sanitation, and destruction of infected debris provide only partial control due to the persistence of sclerotia in soil (Aycock, 1966) [1] . Therefore, chemical fungicides continue to play an important role in disease management. Fungicides such as Mancozeb, Carboxin + Thiram, Propiconazole, Hexaconazole, Tebuconazole, and Carbendazim have been reported to inhibit mycelial growth and suppress disease development caused by S. rolfsii under laboratory and field conditions (Dubey et al., 2012; Mahadevakumar et al., 2016; Deepthi and Reddy, 2013) [28,27] . However, repeated and indiscriminate use of fungicides may lead to environmental contamination, development of fungicide resistance, disruption of beneficial soil microflora, and increased production costs (Brent and Hollomon, 2007). Biological control has emerged as a sustainable and environmentally safe alternative for managing soil-borne pathogens. Among various bio-control agents, Trichoderma viride and Pseudomonas fluorescens have shown considerable potential against S. rolfsii and other soil-borne pathogens (Chet, 1987; Harman et al., 2004; Weller, 2007) [8, 31] . Species of Trichoderma suppress pathogens through mycoparasitism, antibiosis, competition for nutrients and space, and production of cell wall degrading enzymes such as chitinases and glucanases (Elad et al., 1982; Harman et al., 2004) [29,30,8] . Similarly, P. fluorescens contributes to disease suppression through production of antibiotics, siderophores, hydrogen cyanide, lytic enzymes, and induction of systemic resistance in host plants (Weller, 2007; Haas and Défago, 2005) [31,32] . In addition to pathogen suppression, these bio-agents improve root growth, nutrient uptake, and overall plant health, making them important components of integrated disease management programs. Integrated disease management strategies that combine chemical fungicides with biological control agents are increasingly recognized as effective and sustainable approaches for managing soil-borne diseases. Such approaches not only reduce disease incidence but also minimize dependence on chemical pesticides while maintaining crop productivity and soil health (Cook and Baker, 1983; Harman et al., 2004) [8] . Therefore, the present investigation was undertaken to evaluate the efficacy of selected fungicides and bio-agents applied through different methods and timings for the management of foot rot caused by Sclerotium rolfsii in finger millet under field conditions.

Material and Methods

Field experiment was conducted to test the efficacy of selected fungicides which were performed better under in vitro condition in the previous study viz., mancozeb, propiconazole and hexaconazole (Bharath, 2020) [3] . The layout was laid out with the plot size of 3×3m in sick soil by following RBD design. Recommended agronomic practices was followed for better crop stand. 20 days old foot rot susceptible variety Indaf-5 seedlings was transplanted @ 2 seedlings per hill in 10 rows per plot and 30cm apart. Alternative irrigations was given for better establishment of the pathogen. Observations was recorded on growth parameters like, plant height, no of tillers per plant and no of fingers per ear head. Yield parameters like, grain yield and straw yield per plot was recorded at maturity stage and Pathological parameters like, Per cent Disease Incidence (PDI) and basal lesion length was recorded at tillering and flowering stage of the crop. An integrated approach for the management of foot rot of finger millet caused by Sclerotium rolfsiiusing different bioagents and chemicals alone and in combination was carried out under field conditions. Observations on incidence of disease as well as yield parameters were recorded. Field trials were carried out in the experimental field at ZARS, VC Farm, Mandya. The details of the treatments were as given below in Table 1 and Table 2.

Statistical Analysis

Statistical analysis will be done by following the procedure given by Panse and Sukhatme (1985) [13] . The original data in per cent will be converted into angular transformed values, before analysis according to the table given by Snedecor and Cochran (1967) [19] .

Results and discussion

Effect of fungicides and bio-agents on foot rot incidence

The fungicides and bio-agents that exhibited promising inhibitory effects against Sclerotium rolfsii under in vitro conditions were further evaluated under artificially inoculated sick plot conditions at AICRP on Small Millets, ZARS, V.C. Farm, Mandya. Disease incidence was recorded at tillering and maturity stages to assess the effectiveness of different application methods and timings.Significant differences among treatments were observed with respect to foot rot incidence (Table 3). Among the fungicidal treatments, seedling root dip with Propiconazole 25% EC (T₂) recorded the lowest disease incidence at the tillering stage (5.70%), followed by Mancozeb 75% WP (T₁) and Hexaconazole 5% EC (T₃):, both recording 6.73% disease incidence. The superior performance of Propiconazole may be attributed to its systemic action and prolonged protection against pathogen establishment during the early growth stages.

At crop maturity, spraying Propiconazole 25% EC at the collar region 20 days after transplanting (T₅) proved most effective, recording only 8.23% disease incidence, followed by Mancozeb 75% WP spray at 20 DAT (T₄) with 11.80% disease incidence. In contrast, delayed application of fungicides at 40 DAT was comparatively less effective, indicating the importance of timely intervention during the early stages of disease development. Similar observations were reported by Kulkarni and Kulkarni (1994) [10] , Virupaksha Prabhu et al. (1997) [20] , Sheela et al. (1998) [18] , Biswas et al. (2000) [4] , and Patibanda et al. (2002) [14] , who demonstrated the effectiveness of triazole and protectant fungicides against diseases caused by S. rolfsii. The bio-agent treatment comprising seedling root dip and soil application of Trichoderma viride and Pseudomonas fluorescens (T₁₁) recorded the lowest disease incidence among all treatments, with only 3.40% and 6.50% disease incidence at tillering and maturity stages, respectively. Consequently, this treatment achieved the highest disease reduction over untreated control (77.88% at tillering and 89.63% at maturity). The effectiveness of these bio-agents may be attributed to rapid rhizosphere colonization, competition for nutrients and infection sites, production of antibiotics and lytic enzymes, mycoparasitism, and induction of systemic resistance in the host plant (Chet, 1987

Effect on plant growth parameters

Significant improvements in growth parameters were observed in treatments that effectively suppressed foot rot disease (Table 4). Propiconazole spray at 20 DAT (T₅) recorded the maximum plant height (116.83 cm), number of tillers per plant (4.57), and number of fingers per ear head (7.90) among fungicidal treatments. Reduced disease pressure likely facilitated better nutrient uptake, root development, and photosynthetic efficiency, resulting in improved crop growth. The bio-agent treatment (T₁₁) recorded superior growth parameters, including plant height (115.50 cm), number of tillers (5.47), and number of fingers per ear head (8.20). Apart from disease suppression, Trichoderma and Pseudomonas are known to promote plant growth through enhanced nutrient solubilization, phytohormone production, improved root architecture, and induction of plant defense responses (Harman et al., 2004; Haas and Défago, 2005; Vinale et al., 2008) [8] .These findings corroborate earlier reports of Manu (2012) [12] , Basamma (2008) [2] , and Hegde et al. (2010) [9] , who observed enhanced growth and vigor in finger millet and other crops following application of biological control agents against soilborne pathogens.

Effect on grain yield, straw yield and economics

Effective disease management significantly influenced grain and straw yields (Tables 4 and5). Among fungicidal treatments, Propiconazole spray at 20 DAT (T₅) produced the highest grain yield (3069 kg ha ¹) and straw yield (4604 kg ha ¹), followed by Mancozeb ⁻ ⁻ spray at 20 DAT (T₄) with grain and straw yields of 2585 and 3877 kg ha ¹, respectively. ⁻  The highest yield was obtained with the bio-agent treatment (T₁₁), which recorded 3543 kg ha ¹ grain yield and 5314 kg ha ¹ straw yield. Enhanced yields under bio-agent ⁻ ⁻ treatment can be attributed to effective suppression of S. rolfsii coupled with plant growthpromoting effects. Similar observations were reported by Manjunatha and Kiran Babu (2012) [11] , who emphasized the role of integrated biological approaches in managing collar rot diseases while improving crop productivity. The untreated control recorded the lowest grain (1303 kg ha ¹) and straw yield (1955 kg ha ¹), highlighting the severe impact of foot rot ⁻ ⁻ disease on crop productivity. Yield improvements observed under fungicidal and biological treatments were directly associated with reduced disease incidence and improved plant health.  Avoidable yield loss: Avoidable yield loss analysis revealed substantial benefits from disease management interventions (Table 5). Among fungicidal treatments, Propiconazole spray at 20 DAT (T₅) recorded the highest reduction in avoidable grain and straw yield losses, with gains of 135.53% and 140.61%, respectively, over untreated control. The bio-agent treatment (T₁₁) was superior, reducing avoidable grain and straw yield losses by 171.91% and 185.32%, respectively. These results indicate that effective suppression of foot rot disease can substantially improve productivity and reduce economic losses. The findings agree with reports by Pawar et al. (2013) [15] , who documented considerable yield reductions due to foot rot in finger millet under field conditions.

 Benefit-cost ratio: Economic analysis revealed significant differences among treatments. [8] .

Treatment details

 T₁ -Seedling root dip with Mancozeb-75% WP (2g/L) for 30 min during transplantation  T₂ -Seedling root dip with Propiconazole -25% EC (1mL/L) for 30 min during transplantation  T₃ -Seedling root dip with Hexaconazole -5% EC (2mL/L) for 30 min during transplantation  T₄ -Spraying Mancozeb-75% WP (2g/L) at collar region of the plant @20DAT  T₅ -Spraying Propiconazole -25% EC (1mL/L) at collar region of the plant @20DAT  T₆ -Spraying Hexaconazole -5% EC (2mL/L) at collar region of the plant @20DAT  T₇ -Spraying Mancozeb-75% WP (2g/L) at collar region of the plant @40DAT  T₈ -Spraying Propiconazole -25% EC (1mL/L) at collar region of the plant @40DAT  T₉ -Spraying Hexaconazole -5% EC (2mL/L) at collar region of the plant @40DAT  T₁₀ -Soil drenching with Carboxin 37.5% +Thiram 37.5% DS at seedling stage  T₁₁ -Seedling root dip + Soil application with Trichoderma viride + Pseudomonas fluorescens  T₁₂ -Untreated check

Conclusion

The present study demonstrated that both fungicides and bio-agents were effective in managing foot rot of finger millet caused by Sclerotium rolfsii under sick plot conditions. Among the fungicidal treatments, spraying Propiconazole 25% EC (1 mL L ¹) at the collar ⁻ region 20 days after transplanting (DAT) was the most effective, recording disease reduction of 56.21% and 86.87% at tillering and maturity stages, respectively. This treatment also resulted in higher grain and straw yields, maximum reduction in avoidable yield loss (135.53%), and a favorable benefit-cost ratio (1:2.51).However, the combined application of Trichoderma viride and Pseudomonas fluorescens through seedling root dip and soil application proved superior to all fungicidal treatments, recording the lowest disease incidence, highest disease reduction (77.88% and 89.63% at tillering and maturity stages, respectively), maximum grain and straw yields, and the highest benefitcost ratio (1:2.93). The study therefore highlights the potential of integrating these bio-agents as an effective and eco-friendly strategy for sustainable management of foot rot in finger millet. Where immediate disease suppression is required, Propiconazole 25% EC applied at 20 DAT can be recommended as an effective chemical option.

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