Role of bioagents and plant extracts in the management of Alternaria blight of Indian mustard caused by Alternaria brassicae: A comprehensive review

Introduction

Indian mustard (L. Czern. & Coss.) is one of the most economically significant oilseed crops in India, occupying approximately 5.9 million hectares with a production of about 8.0-9.5 million tonnes annually (DRMR, 2023) [4] . India ranks among the top three producers of rapeseed-mustard globally, and the crop contributes nearly 28-30% of the country's total edible oil pool. Mustard is cultivated extensively across the Indo-Gangetic plains, particularly in Rajasthan, Uttar Pradesh, Haryana, Madhya Pradesh, and West Bengal. Despite its agricultural significance, mustard production is severely constrained by various biotic stresses, among which Alternaria blight is considered one of the most devastating foliar diseases. The disease manifests as dark brown to black, concentric-ringed necrotic lesions on leaves, stems, siliquae, and seeds, ultimately reducing photosynthetic efficiency, seed weight, and oil content (Meena et al., 2022) [17] . Under warm humid conditions (temperature 25-30°C, relative humidity >85%), the disease can cause yield losses of 10-70% and seed oil reduction of 5-15% (Gupta et al., 2020) [5] . Historically, disease management has relied heavily on synthetic fungicides such as mancozeb, iprodione, carbendazim, and propiconazole. However, their repeated use has raised concerns regarding pathogen resistance, phytotoxicity, ecological imbalance, residue toxicity in food and environment, and the cost burden on small-scale farmers. Under these circumstances, biocontrol-based and botanical approaches offer promising, sustainable, and economically viable alternatives (Sharma & Saharan, 2021) [29] . Biological control exploits naturally occurring microorganisms, primarily Trichoderma spp. and fluorescent pseudomonas, as antagonists against soil-borne and foliar pathogens.

Botanical fungicides, derived from plant extracts rich in secondary metabolites, provide a broad-spectrum, biodegradable, and locally accessible disease management option. The present review aims to comprehensively synthesize and critically evaluate research on the use of these bioagents and plant extracts for the management of Alternaria blight in Indian mustard.

The Pathogen: Alternaria brassicae 2.1 Taxonomy and Morphology

Alternaria brassicae (Berk.) Sacc belongs to the Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes, Order Pleosporales, and Family Pleosporaceae. Colonies of A. brassicae on potato dextrose agar (PDA) are initially greyish-white to pale olivaceous, becoming dark olivaceousgrey to black with age. Mycelium is septate, branched, and dark brown. Conidiophores are simple or branched, septate, pale to mid-brown, arising singly or in small groups. Conidia are produced in long chains of 4-12 spores, are large, obclavate to oblong-ellipsoidal, with a long beak, measuring 75-350 × 15-22 µm (excluding beak), muriform with 6-13 transverse septa and 0-4 longitudinal septa (Simmons, 1992; Meena et al., 2016) [31,14,15,16] . The large conidia with long beaks are a key morphological feature distinguishing A. brassicae from A. raphani and A. alternata, which also infect cruciferous crops.

Area of Production and Economic Importance

Mustard is grown across diverse geographical regions with India being the world's largest producer, consumer, and exporter of mustard seed. According to recent agricultural statistics, mustard cultivation in India covers approximately 7.5-8.5 million hectares annually with production around 11-12 million metric tons. Major mustard-producing states include Rajasthan (contributing ~25% of national production), Madhya Pradesh, Odisha, Uttar Pradesh, and Haryana (Ministry of Agriculture, 2022). Globally, the primary mustard producers are India (contributing approximately 11 million tons), Canada (3-4 million tons), China (3 million tons), and the European Union countries. Mustard production serves multiple purposes: edible oil production (main use), spice and condiment preparation, animal feed through cake residue, and increasingly in industrial applications. The crop's economic value in India exceeds Rs. 35, 000-40, 000 crores annually, making it a crucial component of the agricultural economy, particularly for smallholder and marginal farmers in semi-arid regions. The yield potential of mustard ranges from 1.0-2.0 tons/hectare, but actual productivity remains suboptimal due to biotic stresses, particularly fungal diseases. Alternaria brassicae-induced losses reduce productivity by approximately 20-40% in non-endemic areas and up to 90% in areas with high disease pressure. Given the economic significance and dietary importance of mustard, implementing effective disease management strategies is crucial for maintaining stable production and ensuring food security.

Disease Cycle and Epidemiology

The pathogen primarily survives on infected crop debris, seeds, alternate brassica hosts, and volunteer plants. Conidia germinate in the presence of free moisture and penetrate host tissue directly through the cuticle or via stomata. The disease cycle involves initial infection (primary inoculum from seed or debris), lesion development, sporulation (secondary inoculum), and airborne dispersal. The incubation period ranges from 3 to 7 days depending on environmental conditions. Environmental conditions such as temperatures between 18-27°C and relative humidity above 80% favor rapid disease development. The necrotrophic nature of the pathogen makes disease management particularly difficult because the fungus benefits from host cell death during infection. The pathogen overwinters in infected plant residues, soil, and seeds, serving as primary sources of inoculum for the subsequent season. Crop debris contamination and survival of fungal propagules in soil can persist for extended periods, complicating disease management in the field.

Biological Control: Mechanisms and Overview

Biological control of plant diseases involves the use of living organisms or their metabolites to suppress pathogen populations and disease incidence. The main mechanisms employed by biocontrol agents (BCAs) include: (i) mycoparasitism-direct hyphal penetration and lysis of the pathogen; (ii) antibiosis-production of volatile and nonvolatile antibiotics, cell wall-degrading enzymes (CWDEs), and secondary metabolites toxic to pathogens; (iii) competition for nutrients and space; (iv) induction of systemic resistance (ISR or SAR) in host plants; and (v) plant growth promotion through phytohormone production, phosphate solubilization, and siderophore secretion (Harman et al., 2019) [7] . Biocontrol agents are increasingly being formulated as wettable powders (WP), talc-based formulations, liquid biofungicides, and seed coat products for field application.

Role of Trichoderma viride in Disease Management

Trichoderma viride is one of the most widely used fungal bioagents for the management of soil-borne and foliar plant pathogens. The fungus suppresses pathogens through several mechanisms including mycoparasitism, competition for nutrients and space, production of antibiotics, and induction of host resistance. Studies have shown that T. viride effectively inhibits mycelial growth and sporulation of A. brassicae under in vitro conditions. The antagonistic activity of T. viride is mainly attributed to its ability to produce hydrolytic enzymes such as chitinases, glucanases, and proteases that degrade fungal cell walls. In addition, the bioagent secretes secondary metabolites with antifungal properties that suppress pathogen growth. Application of T. viride as seed treatment or foliar spray has resulted in reduced disease severity and enhanced plant vigor in mustard crops. Moreover, the fungus improves nutrient availability and root growth, thereby promoting overall plant health and tolerance against pathogen attack. Studies have also reported that volatile organic compounds released by T. viride significantly reduce conidial germination and germ tube elongation of A. brassicae, thereby limiting early infection establishment. Furthermore, its rapid colonization ability enables it to outcompete the pathogen for nutrients, making it an effective preventive biocontrol strategy under both laboratory and field conditions.

Role of Trichoderma harzianum in Disease

Management: Trichoderma harzianum is another important fungal antagonist extensively studied for biological control of plant diseases. Similar to T. viride, it exhibits multiple mechanisms of pathogen suppression including antibiosis, mycoparasitism, and induced systemic resistance. The fungus colonizes the rhizosphere effectively and competes aggressively with plant pathogens for nutrients and ecological niches. In dual culture assays, Trichoderma harzianum consistently exhibits strong mycoparasitic behaviour, characterized by coiling of its hyphae around the pathogen hyphae, followed by penetration and subsequent lysis of the host cells. This antagonism is further supported by the production of both volatile and non-volatile inhibitory metabolites (Benhamou & Chet, 1993; Harman et al., 2004; Poveda, 2021) [1,6,25] .

Antagonistic Mechanisms Against A. brassicae

Several studies have reported that T. harzianum significantly inhibits radial growth and sporulation of A. brassicae. The bioagent produces volatile and non-volatile metabolites that adversely affect fungal development. Furthermore, T. harzianum stimulates host defense mechanisms by activating defense-related enzymes and strengthening structural barriers against infection. Its ability to survive under diverse environmental conditions and compatibility with organic farming practices make it a valuable component of sustainable disease management programs (Harman et al., 2004) [6] .

Role of Bacillus subtilis in Disease Management

Bacillus subtilis is a beneficial rhizobacterium known for its strong antagonistic activity against numerous plant pathogens. The bacterium suppresses fungal pathogens through production of antibiotics, lipopeptides, siderophores, and hydrolytic enzymes. In the case of Alternaria blight, B. subtilis has shown remarkable ability to inhibit conidial germination and mycelial growth of A. brassicae. [41] reported that culture filtrate of B. subtilis at 10% concentration inhibited mycelial growth by 68.7% and conidial germination by 72.4%. Tiwari and Tiwari (2017) [35] demonstrated that seed treatment with B. subtilis (10⁹ cfu/mL) significantly reduced seed-borne infection by 71.3% and improved seedling vigour index. Foliar spray of B. subtilis wettable powder (10⁸ cfu/mL) reduced disease incidence by 54.8% and severity by 49.6% under field conditions. Combination of B. subtilis with T. harzianum demonstrated synergistic inhibition of the pathogen, with 84.6% mycelial growth inhibition (Meena et al., 2016) [14,15,16] . The bacterium produces antimicrobial compounds such as surfactin, iturin, and fengycin, which disrupt fungal cell membranes and inhibit fungal development. In addition to direct antagonism, B. subtilis induces systemic resistance in plants by activating defense-related pathways involving salicylic acid and jasmonic acid signaling. Seed treatment and foliar application of B. subtilis formulations have resulted in reduced disease incidence and enhanced plant growth in mustard crops (Verma et al., 2014). Due to its rapid multiplication and environmental adaptability, B. subtilis is considered an effective biological control agent for integrated disease management.

Yadav et al. (2015)

Role of Pseudomonas fluorescens in Disease

Management: Pseudomonas fluorescens is a plant growth-promoting rhizobacterium widely recognized for its biocontrol potential against fungal diseases. The bacterium suppresses pathogens through production of antibiotics, hydrogen cyanide, siderophores, and various antifungal metabolites. Several studies have demonstrated that P. fluorescens effectively reduces the growth and sporulation of A. brassicae. One of the important mechanisms of P. fluorescens is the induction of systemic resistance in host plants. The bacterium enhances plant defense responses by stimulating the production of defense enzymes such as peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase. These defense responses strengthen plant resistance against pathogen invasion. In addition to disease suppression, P. fluorescens promotes plant growth through improved nutrient uptake and phytohormone production. Its dual role as a growth promoter and disease suppressor makes it highly valuable for sustainable agriculture.

Role of Plant Extracts (Botanical Fungicides)

Plant-derived extracts (botanicals) represent an ancient and increasingly validated approach to plant disease management. They contain complex mixtures of secondary metabolites-alkaloids, terpenes, phenolics, flavonoids, essential oils, and glycosides, that collectively or individually exert antifungal effects through multiple mechanisms including disruption of cell membrane integrity, inhibition of spore germination, interference with metabolic pathways, and induction of host resistance (Doughari, 2015; Patel & Ingle, 2022) [3,23] . Their broadspectrum bioactivity, biodegradability, low mammalian toxicity, and local availability make them highly attractive for disease management in resource-limited farming systems.

Neem (Azadirachta indica) Active Constituents and Mechanism

Neem (Family: Meliaceae) is among the most extensively studied botanicals for the management of Alternaria blight. Neem leaf and seed kernel extracts contain bioactive compounds such as azadirachtin, nimbolide, nimbin, and salannin. These compounds interfere with fungal ergosterol synthesis (analogous to sterol demethylation inhibitors), inhibit spore germination and germ tube elongation, and disrupt cell membrane permeability (Mishra & Singh, 2020) [18] . Commercial neem-based formulations, including neem oil emulsions and aqueous neem extracts, are readily available and relatively affordable. The main limitations include variability in bioactive compound concentrations depending on plant part used, extraction method, and storage conditions. Standardization of neem extracts regarding azadirachtin content and development of stabilized formulations remain ongoing research priorities.

Efficacy Studies

At 10-15% concentration, aqueous NLAE inhibits mycelial growth by 65-80% in vitro (Chaudhary & Sinha, 2021) [2] . Commercially formulated neem oil (0.5-1.0%) reduces conidial germination by 75-90% within 24 h. In field trials in Rajasthan, three foliar sprays of NKE (5%) at preflowering, early pod, and pod-filling stages reduced Alternaria blight severity by 52-64% compared to unsprayed controls, with yield improvement of 15-22% (Patel et al., 2022; Yadav & Singh, 2021) [24,39] . Shukla et al. (2022) found that neem oil (5%) and neem leaf extract effectively reduced disease severity and improved growth and yield parameters in mustard. Field trials conducted by Meena et al. (2016) demonstrated that three sprays of NSKE (5%) at 15-day intervals during crop growth significantly reduced disease severity index from 58.3% (untreated) to 29.6% (NSKE-treated), with no phytotoxic effects. Neem oil (3%) was found to be superior to neem leaf extract, with Yadav et al. (2018) reporting 80.5% inhibition of mycelial growth under in vitro conditions. The broad-spectrum activity and ISR-inducing capability of neem extracts make them especially valuable in integrated disease management. Neem oil (3-5% emulsion) and leaf extract (10-20%) significantly reduce A. brassicae sporulation and spore germination in vitro. Field trials demonstrate 35-70% disease reduction, with effectiveness increasing with higher concentrations and frequent applications. The broadspectrum nature of neem provides additional benefits against insect pests and other fungal pathogens (Ponomarenko et al., 2011).

Ginger (Zingiber officinale) Active Constituents and Mechanism

Ginger rhizomes (Family: Zingiberaceae) contain bioactive phenylpropanoids, gingerols (6-, 8-, 10-gingerol), shogaols, zingerone, paradol, and essential oil components (zingiberene, β-bisabolene). 6-gingerol and its dehydration product 6-shogaol are particularly effective antifungal agents acting by disrupting fungal cell membranes and inhibiting ergosterol biosynthesis (Mohammadi et al., 2021) [20] . These compounds also exhibit anti-sporulation activity.

Efficacy Studies

Ginger rhizome extract (10-20%) inhibits mycelial growth by 48-65% in vitro. At 15% concentration, spore germination inhibition reaches 70-80%. Acetone extract of ginger at 2000 µg/mL demonstrated 78% inhibition of conidial germination (Jain et al., 2022) [9] . When combined with neem extract in field sprays, the mixture showed synergistic effects with 68-72% disease suppression. Singh et al. (2013) [34] reported that aqueous ginger extract at 10% and 20% concentrations inhibited mycelial growth of A. brassicae by 52.6% and 68.4%, respectively, under in vitro conditions. Conidial germination was suppressed by 60.2% at 20% concentration. Tiwari and Tiwari (2017) [35] found that ethanolic ginger extract at 15% concentration caused 72.8% inhibition of mycelial growth. Foliar application of ginger extract (10%) reduced Alternaria blight incidence by 41.3% in field trials. The antiinflammatory and antioxidant properties of gingerols may also contribute to induced plant defence responses.

Garlic (Allium sativum) Active Constituents and Mechanism

Linn. (Family: Amaryllidaceae) contains alliin which is converted to allicin (diallyl thiosulfinate) by the enzyme alliinase when it is crushed. Allicin is a broad-spectrum antifungal compound. The organosulfur compounds such as allicin, diallyl disulfide (DADS), diallyl trisulfide (DATS), and ajoene, which are found in garlic, have been used in traditional medicine for a long time. The antimicrobial activity of these compounds is strong against bacteria and fungi and other microorganisms. Allicin, which is produced by the enzymatic reaction of alliin during the damage of garlic tissue, has a short time period of action and its primary effect is a rapid inhibition of the synthesis of fungal cell wall and the disruption of the cellular respiration of pathogenic fungi. Another bioactive antifungal component of garlic oil is Ajoene, Diallyl disulfide (DADS), and Diallyl trisulfide (DATS). However, garlic extracts are susceptible to degradation following exposure to light and heat, necessitating storage under controlled conditions. Development of stabilized formulations of organosulfur compounds represents an important research direction for improving practical applicability and consistency of garlic-based biocontrol products.

Efficacy Studies

Garlic bulb aqueous extract (5-20%) inhibits mycelial growth by 70-88% in vitro, making it one of the most potent botanical extracts evaluated against this pathogen (Sharma & Dubey, 2021) [28] . Conidial germination inhibition exceeds 90% at 15% extract concentration. In field trials, three sprays of garlic extract (10%) at 10-day intervals from disease initiation onwards reduced disease severity by 60-72% and improved mustard seed yield by 18-24% over untreated plots (Meena et al., 2022; Singh & Yadav, 2020) [17, 32] .

Turmeric (Curcuma longa) Active Constituents and Mechanism

Linn. (Family: Zingiberaceae) rhizomes are rich in curcuminoids (curcumin, demethoxycurcumin, bisdemethoxycurcumin), volatile essential oils (turmerone, zingiberene, ar-turmerone) and polysaccharides. Curcumin has been found to inhibit the synthesis of ergosterol, a component of the cell membrane of fungi, and the germination of fungal spores. The main yellow polyphenol curcumin displays antifungal activity by creating oxidative stress in fungal cells, inhibiting mitochondrial dehydrogenase, cell wall synthesis and interfering with fungal virulence factors, protease & lipase (Tran et al., 2020) [36] . The main limitation of curcumin-based products is low bioavailability due to poor aqueous solubility and rapid degradation. Development of nano-formulations and use of bioavailability enhancers such as piperine (from black pepper) have been explored to improve efficacy and practical applicability of curcumin-based fungicidal preparations.

Efficacy Studies

The rhizome powder extract of turmeric was found to be effective in inhibiting in vitro by 50-68%. Conidial germination and germ tube growth were shown to be significantly inhibited by curcumin at 200-500 µg/mL. The aqueous extract of turmeric was applied as a field spray at 5% concentration and the incidence of Alternaria blight was reduced by 42-55% when tested in different locations of Uttar Pradesh at fortnightly intervals (Rani et al., 2021). When combined with garlic extract, the phytochemical mixture showed complementary antifungal activity (Sharma et al., 2023). Karthikeyan et al. (2022) reported that turmeric extract at 15% concentration recorded 74.26% inhibition of mycelial growth of A. brassicae under in vitro conditions.

Tulsi (Ocimum sanctum / Ocimum tenuiflorum) Active Constituents and Mechanism

The Tulsi leaf extract contains eugenol (70 -80% of the essential oil), eugenol oxide, methyl eugenol, βcaryophyllene, ursolic acid, rosmarinic acid and flavonoids like orientin and vicenin. The antifungal activity stems from the ability of eugenol to inhibit branching of hyphae, inhibit mycelial growth, and cause mitochondrial dysfunction at minimal inhibitory concentrations (MIC) of 0.5-2.0 mg/mL (Rao et al., 2020) [27] .

Efficacy Studies

In vitro, the leaf aqueous extracts of tulsi have been seen to inhibit the mycelial growth by 55-72% at 10-20% concentration. The essential oil (500 µg/mL) inhibited conidial germination by 88% (Kumar et al., 2023) [11] . Mustard 10% leaf extract application at fortnightly intervals in the field significantly reduced the disease incidence and severity by 45-58% in Madhya Pradesh (Pandey & Dixit, 2021) [22] .

Other Botanicals with Reported Activity

In addition to the major botanicals discussed above, several other plant-derived extracts have exhibited considerable antifungal potential against Alternaria brassicae, although they have received comparatively less research attention. These include Lantana camara leaf extract (40-62% inhibition at 10% concentration), Calotropis procera latex (55-70%), Eucalyptus globulus leaf extract (45-60%), Withania somnifera root extract (48-55%), Aegle marmelos leaf extract (42-58%), Datura stramonium leaf extract (50-65%), and Pongamia pinnata seed extract (40-55%). The inhibitory effects of these botanicals indicate their potential as eco-friendly alternatives for the management of Alternaria blight in mustard. These botanicals warrant further field-level validation. Extracts at 10-20% concentration have shown 50-65% inhibition of A. brassicae growth in vitro. Chilli pepper (Capsicum annuum) extracts, rich in capsaicinoids, exhibit antifungal properties. Capsicums contain capsaicin and related compounds with pronounced antifungal activity. Extracts at 30-50% concentration inhibit A. brassicae conidial germination and mycelial growth by 60-80%. The aqueous and alcoholic extracts are both effective, though the alcoholic extracts are often more potent. An application frequency of 7-10 days provides good disease control under field conditions.

Formulation and Application Strategies 5.1 Plant Extract Formulations

Plant extracts can be formulated as aqueous, alcoholic, or oil-based preparations. Aqueous extracts are economical and suitable for spray application but have limited persistence. Stabilization using emulsifiers, surfactants, or adhesive agents improves spray retention and efficacy. Encapsulation of volatile compounds in nano-particles enhances stability and controlled release. Standardization of extract concentrations to ensure consistent active compound levels is essential for reproducible results and regulatory approval.

Bioagent Formulations

The commercial bioagent formulations are powder, granular, and liquid (aqueous or oil-based). Talc-based formulations have a variable spore viability, are inexpensive, and have good shelf-life. Liquid formulations are more concentrated and give more viable cells and spray coverage, but must be refrigerated and stored. Formulations that include biochar, clay minerals, and polymers are new formulations that extend shelf-life without compromising viability. Reduce the amount of the products used by applying bioagents to the seed (biopriming) to protect the crop in early season. A combination of complementary bioagents in a multi-strain formulation provides greater coverage of pathogens and minimizes risk of resistance development.

Mechanisms of Bioagents

Bioagents control A. brassicae through multiple interrelated mechanisms. (i) Mycoparasitism involves the direct attack on pathogen hyphae and spores via coiling, penetration, and subsequent cell wall degradation. (ii) Antibiosis refers to the synthesis of both volatile and non-volatile secondary metabolites that suppress pathogen growth. (iii) Competition occurs through rapid colonization of the phyllosphere and rhizosphere, thereby limiting access of the pathogen to nutrients and space. (iv) Induced Systemic Resistance (ISR) enhances the plant's innate defense system by activating signaling pathways mediated by salicylic acid (SA) and jasmonic acid/ethylene (JA/ET). (v) Enzymatic activity includes the production of cell wall-degrading enzymes such as chitinases, β-1, 3-glucanases, and proteases that disrupt pathogen structural integrity (Meena et al., 2016; Singh et al., 2014) [14,15,16,33] .

Integrated Disease Management (IDM)

The integration of bioagents with plant-derived extracts offers an effective IDM strategy by targeting pathogens through multiple mechanisms at the same time, minimizing the likelihood of resistance development, and delivering a wider range of complementary activities against the pathogen. Studies have demonstrated significantly enhanced disease suppression when seed treatment was combined with garlic or neem foliar sprays, reducing Alternaria blight severity by 70-78% compared to 50-65% with either treatment alone (Rana & Sood, 2022) [26] . Integrated disease management strategies involving seed treatment with bioagents followed by foliar application of botanical extracts have demonstrated considerable reduction in disease incidence and improvement in yield parameters. Furthermore, integration of these biological approaches with cultural practices such as crop rotation, timely sowing, and field sanitation can provide long-term and sustainable disease management. Monitoring of disease development through regular crop inspection and use of weather-based disease prediction models enables targeted interventions at appropriate times, maximizing efficacy while minimizing input costs and environmental impact. Farmer field schools and participatory research approaches have proven effective in promoting adoption of IPM practices among smallholder mustard growers.

Recent Advances and Future Perspectives

The development of biotechnology and microbiological research has opened up new possibilities of enhancing the efficiency of plant extracts and bioagents in disease management.

Nanotechnology-based formulations, microbial consortia, and encapsulated bioagents are being developed to improve stability and field performance. Molecular research into host-pathogen interactions and microbial antagonism is also aiding in the discovery of novel antifungal agents and mechanisms of disease suppression (Mukherjee et al., 2019) [21] . The latest advances in the field are: (i) nano-bioformulations with chitosan or silica nanoparticles for improved delivery and longevity of Trichoderma and Bacillus; (ii) genomic/transcriptomic characterization of biocontrol gene clusters specific for Alternaria suppression; (iii) enhancement of biocontrol traits of Trichoderma using CRISPR technology; (vi) nano-emulsified botanical formulations with enhanced rainfastness and photostability; (iv) the selection of elite biocontrol strains based on metabolomic profiling of 2, 4-diacetylphloroglucinol (2, 4-DAPG), lipopeptides, and volatile organic compounds associated with rainfastness and photostability; (v) the development of synergistic biocontrol consortia comprising Trichoderma, Bacillus, and Pseudomonas for multi-target disease suppression; (vi) formulation of nano-emulsified botanical products with improved rainfastness and photostability. The ability to integrate precision agriculture tools (disease forecasting models, remote sensing-based disease detection) with the timing of bioagent and botanical application should greatly enhance the efficacy of a field and reduce resource use efficiency (Verma et al., 2024; Kumar et al., 2024) [37,12] .

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36. Tran TN, Tran TT, Nguyen TA, Pham TV. Antifungal activity of curcumin and its molecular mechanism: a review. Molecules. 2020;25(24):5990.
37. Verma J, Yadav B, Singh D. Nano-encapsulated botanicals for improved disease management in Indian mustard: current status and future directions. Industrial Crops and Products. 2024;212:118356.
38. Yadav MK, Prabha K, Chand R. In vitro efficacy of some plant extracts against seed-borne Alternaria brassicae of Indian mustard. Annals of Plant Protection Sciences. 2020;28(1):53-58.
39. Yadav S, Singh K. Comparative efficacy of neem-based products against Alternaria blight of Indian mustard under field conditions. Indian Journal of Plant Protection. 2021;49(2):112-119.
40. Yadav S, Ameta BL, Meena PD. Integrated management of Alternaria blight of mustard using bioagents and botanical extracts. Journal of Oilseed Brassica. 2018;9(1):45-54.
41. Yadav SV, Singh HV, Ameta BL. Evaluation of bioagents and plant extracts for management of Alternaria blight of mustard. Indian Phytopathology. 2015;68(4):385-390.
42. Yadav VK, Kumar A, Choudhary M. Seed treatment with Trichoderma harzianum formulations for management of Alternaria blight of mustard: dose standardization and mechanism study. Biological Control. 2023;180:105195.