Efficacy of plant extract and Biocontrol agents against powdery mildew of mustard (Brassica juncea (L.)

Introduction

Indian mustard (Brassica juncea (L.) Czern. & Coss.) is an important oilseed crop of the family Brassicaceae, with a chromosome number of 2n = 36 (Rai et al., 2022) [11] . Rapeseedmustard is the fourth-largest oilseed group globally, while India is a major producer, with Rajasthan contributing the largest share of national production. Mustard productivity is affected by several biotic stresses, among which powdery mildew caused by Erysiphe cruciferarum is an important disease. The pathogen produces characteristic white powdery growth on leaves and other aerial parts and can cause considerable reductions in seed yield and oil content. Disease development is favoured by moderate temperature, low relative humidity and dry weather conditions (Meena et al., 2018 and Verma et al., 2023) [7,15] . Although chemical fungicides are effective against powdery mildew, their repeated use may lead to fungicide resistance, environmental pollution and residue problems. Therefore, ecofriendly alternatives such as biocontrol agents and plant extracts have gained importance. Bioagents including Trichoderma spp., Pseudomonas fluorescens and Bacillus subtilis, along with botanicals such as neem and garlic extracts, have demonstrated antifungal potential (Woo et al., 2023 and Nanjundan et al., 2020) [16,10] .

Materials and Methods

The present study entitled "Efficacy of Plant Extract and Biocontrol Agents Against Powdery Mildew of Mustard (Brassica juncea (L.)" various experiments were conducted at Department of Plant Pathology, School of Agricultural, Suresh Gyan Vihar University, Jaipur, Rajasthan. The experimental plot was laid out in a Randomized block design (RBD) having three replications for each treatment. Mustard variety 'NRCHB-506' show increased susceptibility to powdery mildew disease was used for field trial.

All recommended agronomic practices were followed during whole cropping season. The treatments was used for evaluated the efficacy of plant extracts and bio-agents against powdery mildew viz., T 1-Neema extract (10%), T 2 -Karanj extract (10%), T 3 -Garlic extract (10%), T 4 -Trichoderma harzianum (10 g/l), T 5 -Pseudomonas fluorescens @ 10 g/l, T 6 -Bacillus subtilis @ 10 g/l and T 7 -Control (water spray). Disease incidence of powdery mildew was recorded periodically after the appearance of first disease symptoms in the field. Observations was taken randomly from selected ten plants in each plot. The number of infected plants showing typical symptoms of powdery mildew were counted and expressed as percentage. The disease incidence were calculated using the following formula:

Number of infected plants

Total number of plants observed X 100 Disease severity was assessed using a standard disease rating scale based on the percentage of leaf area covered by powdery mildew infection. Data on severity of powdery mildew was recorded by recommended rating scale (0-5) on ten randomly selected plants from each plot/replication at regular intervals till the maturity of the crop. A disease rating scale (0-5) was used for assessment of disease severity as follows: Disease severity was expressed as percent Disease Index (PDI) using the following formula (Mckinney, 1923) [17] PDI = £ Sum of Indivaual rating Total number of plant observed x Maximum rating X 100

Seed yield of net plot area of each plot was recorded after harvest of the crop. percent increase in seed yield in each treatment over the control was also worked out by following formula.

Yield in Treatment -Yield in control

The data recorded during the investigation were subjected to statistical analysis following the procedure described by Panse and Sukhatme (1967) [18] for Randomized Block Design (RBD).

Results and Discussion

The efficacy of different plant extracts and bio-agents against were evaluated powdery mildew of mustard under in-vivo conditions. The results revealed that all the treatments significantly reduced disease severity and increased disease control over the untreated control. Among the different treatments, Trichoderma harzianum @ 10 g l⁻¹ (T 4 ) proved to be the most effective bio-agent which recorded the significantly lowest disease severity (24.86% PDI) and the highest disease control (47.77%) followed by Pseudomonas fluorescens @ 10 g l⁻¹ (T₅), (26.50%) with 44.33 percent disease control. Bacillus subtilis @ 10 g l⁻¹ (T₆) (28.14%) with 40.88 percent disease control. Among the botanical extracts, garlic extract (10%) (T₃) was found significantly which recorded 31.05 percent PDI and 34.77 percent disease control, followed by neem extract (10%) (T₁) (35.15%) and 26.16 percent disease control. The karanj extract (10%) (T₂) was comparatively less effective which recorded 37.20 percent PDI and 21.85 percent disease control. The untreated control (T₇) recorded the highest disease severity (47.60% PDI) and no disease control. The data presented in Table 1 further indicated that all the treatments significantly increased seed yield over the untreated control. The highest seed yield (19.26 q ha⁻¹) and maximum yield increase (24.18%) were recorded with Pseudomonas fluorescens @ 10 g L⁻¹ (T₅) followed by Trichoderma harzianum @ 10 g l⁻¹ (T₄), (18.22 q ha⁻¹) with 17.47 percent yield increase. Bacillus subtilis @ 10 g L⁻¹ (T₆) (17.78 q ha⁻¹) seed yield with 14.64 percent yield increase, while garlic extract (10%) (T₃) recorded 17.68 q ha⁻¹ seed yield and 13.99 percent yield increase. Neem extract (10%) (T₁) and karanj extract (10%) (T₂) recorded seed yields of 16.96 and 16.45 q ha⁻¹, with corresponding yield increases of 9.35 and 6.06 percent, respectively. The lowest seed yield (15.51 q ha⁻¹) was recorded in the untreated control (T₇). These findings clearly indicated that effective suppression of powdery mildew resulted in a corresponding increase in seed yield and productivity of mustard.

The superior performance of Pseudomonas fluorescens may be attributed to its effective colonization, production of antimicrobial metabolites, competition for nutrients and induction of systemic resistance, thereby restricting pathogen establishment (Mukherjee et al., 2022) [9] . Similarly, Trichoderma harzianum suppresses pathogens through mycoparasitism, antibiosis, nutrient competition and production of cell wall-degrading enzymes (Mukherjee et al., 2022; Singh et al., 2024) [9,14] . The better performance of garlic extract could be due to allicin and other organosulfur compounds, which inhibit fungal growth and spore germination (Borlinghaus et al., 2014; Bayan et al., 2014) [2,1] . The present findings are in agreement with Meena (2013) [6] and Singh et al. (2015) [13] , who reported effective suppression of powdery mildew by Trichoderma and Pseudomonas. Lomate et al. (2014) [4] and Modak et al.

(2019) [8] also observed significant disease reduction with biological agents. The superior efficacy of garlic extract corroborates Choudhary et al. (2025) [3] , who reported maximum powdery mildew suppression with garlic extract. Similar effectiveness of Trichoderma harzianum and Pseudomonas fluorescens was reported by Meena et al.

(2024) [5] and Sharma and Yadav (2024) [12] . Overall, the results indicate that biocontrol agents and garlic extract have considerable potential as eco-friendly components for managing powdery mildew of mustard.

Conclusion

Based on the present investigation, Trichoderma harzianum and Pseudomonas fluorescens can be effectively utilized for eco-friendly management of powdery mildew in mustard, with garlic extract as a promising botanical alternative.

References

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