The exploitation of antagonistic microbial populations could be the answer for the eco-friendly and successful management of plant diseases. In the present study, the efficacy of native rhizobacterial strains of Bacillus subtilis (PR-19 and B-11) solely or in consortia with Pseudomonas aeruginosa (strain GP8) was evaluated for the improvement of plant health and management of web blight disease in cowpea. The application of microbial consortia Bacillus subtilis (B-11) with Pseudomonas aeruginosa (GP8) through talc-based bioformulation showed 41.72% and 45.29% percentage disease control in 2020 and 2021, respectively, suggesting the potential of utilizing location-specific inoculation strains to obtain an optimum symbiotic benefit. The plant growth and yield parameters of cowpea plants were significantly increased in the treatments comprising PGPR-based bioformulations as compared to the chemical fungicide (Carbendazim 50% WP) and control treatments. The combination of seed treatment followed by soil application of consortia (B-11 and GP-8) performed very well at the field level for enhancing plant growth as well as suppressing web blight disease and increasing the yield of cowpea crops. Further research should be carried out on the shelf-life and cost-effectiveness of the prepared bioformulation, as well as their feasibility to be used in integrated disease management programs.

Web blight, biocontrol, Bacillus, Pseudomonas, PGPR, sustainable agriculture.

With the rise of the population, the demand for food is increasing, whereas the modern-day intensive agricultural system, along with the application of chemical pesticides, results in considerable environmental pollution and unavoidable impacts on soil, water, and animals, as well as on human health (Sharma et al., 2020; Raffa and Chiampo 2021). However, the need for pest and disease management is unavoidable to secure our food requirements. Therefore, the development of biopesticide-based pest management strategies is preferred and encouraged globally to ensure food safety as well as food security (Samada and Tambunan 2020). There are different types of biopesticides, like bio-derived chemicals (pyrethrum, rotenone, neem oil, etc.), various essential oils, entomopathogenic fungi, viruses, microbial pesticides, plant growth-promoting rhizobacteria (PGPR), etc. (Boye and Arcand 2013).

PGPRs are remarkable biopesticides, as they not only control several plant diseases but also promote plant health (Gupta et al., 2021). They colonize the plant root rhizosphere and can multiply and maintain their population. PGPR can promote plant growth and development by releasing plant growth regulators or other active compounds and uptake of nutrients through fixation and mobilization. They can minimize the pathogen population by means of competition, antibiosis, or inducing systemic resistance in plants (Riaz et al., 2021). They also play an important role in soil fertility. Some examples of PGPR include Rhizobium, Acetobacter, Azospirillum, Arthrobacter, Azotobacter, Bacillus, Pseudomonas, Micrococcus, etc. (Mashabela et al., 2022). Among different PGPRs, Bacillus sp. has been found effective against several fungal and bacterial pathogens as well as inducing resistance against several abiotic stresses (Egamberdieva, 2016). Bacillus is a gram-positive aerobic endospore-forming genera that is capable of antibiotic production, the production of various enzymes like pectinase, cellulase, and various proteolytic enzymes, nitrogen fixation, and good plant growth-promoting activities, along with biological control through antibiosis and lysis (Kumar et al., 2012). The gram-positive bacterial genus Bacillus sp. is the dominant component of the soil microflora and is found in widely varying habitats. The successful application of Bacillus sp. as bioinoculants depends to a great extent on their capability to colonize roots and compete with the indigenous microbiome in the rhizosphere (Babalola et al., 2021). It is characterized as important because of its biocontrol ability against several disease-causing plant pathogens. Bacillus sp. can control a wide range of soil-borne fungi through antibiotics, enzymes, volatile and non-volatile compounds, or by triggering systemic resistance in the plant (Garcia-Gutierrez et al., 2013). The glittering promise of Bacillus sp. in biological control is exemplified by many research works, yet very few studies are made on region-specific effective Bacillus sp. On the other hand, Pseudomonas species are widely distributed in nature and possess numerous qualities that make them the ideal PGPR (Singh et al., 2019). The fluorescent Pseudomonas is gram-negative, aerobic, rod-shaped, motile, and capable of producing a water-soluble yellow-green pigment. They can thrive in both rhizospheres and rhizoplanes. They show great compatibility with Bacillus and efficiently suppress plant diseases (Singh et al., 2021). Plant growth-promoting rhizobacteria are subjected to variations in climatic and soil factors, climatic factors like rainfall pattern, temperature, and relative humidity, and soil factors like soil temperature, pH, soil moisture, and organic matter, affecting the number of viable microorganisms available in or near the rhizosphere (Yuliatin et al., 2019). All these factors restrict the application of specific strains to specific agro-climatic regions. The application of location-specific strains needs to be emphasized to obtain an optimum symbiotic benefit. Uncountable specificity of different isolates of Bacillus is present due to variation in different agro-climatic zones, which makes it difficult to enumerate successful and effective Bacillus and its application procedures. Enormous research has been conducted on Bacillus spp. as a bio-control agent, but the exploration of native agro-climatic region-specific Bacillus spp. in eastern India is rare. Therefore, the objective of the present study is to evaluate the efficacy of native rhizobacterial strains of Bacillus subtilis solely or in consortia with Pseudomonas aeruginosa (strain GP8) for the improvement of plant health and management of web blight disease in cowpea (Vigna unguiculata (L.) Walp.).

Rhizobacterial strains

Potential strains of native rhizobacterial Bacillus subtilis (B-11and PR-19) and Pseudomonas aeruginosa (GP-8) were collected from The Department of Plant Pathology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia-741252, West Bengal, India, and used in the present investigation.

Maintenance of PGPR

Actively grown PGPR bacteria (Bacillus and Pseudomonas) cultures were transferred to nutrient-agar Petri plates using a sterilized inoculating wire loop following standard bacteriological procedure. The Pseudomonas strain was collected from the Department of Plant Pathology, Bidhan Chandra Krishi Viswavidyalaya, India. Subsequently, it was then incubated at 28 ± 2oC for 72 h to obtain active growth. Thereafter, they were kept in a refrigerator (4 ±1 °C) for future use. Sub-culturing was performed at 15-day intervals to maintain an active bacterial population for future use. 

Preparation of bacterial broth: The nutrient broth was prepared for the mass multiplication of the bacteria. The broth was inoculated with the native rhizobacterial strains Bacillus subtilis (B11 and PR19) and Pseudomonas aeruginosa (GP-8) and incubated in shaker fitted BOD incubator at 28±2°C for 48 h. These homogenized bacterial cultures were utilized further in the experiments.

Bio formulation of PGPR. Talc is widely used as an inorganic carrier for bioformulation of different PGPR/Bio agents. PGPR formulation was prepared using1kg of talc powder mixed uniformly with 150 mL of homogenized broth of bacterial culture manually with proper safety measures. After reaching optimum moisture conditions, the bio-inoculated talc powder was stored in moisture-proof packaging (aluminum bags) and kept in a cool place for future use. 

Field experiments. The field experiments were conducted for two years (2020 and 2021) at Instructional Farm, BCKV, Mohanpur, Nadia, West Bengal, India (located at 22.56"52" (N) latitude and 88.32"20"(E) longitude with an elevation of 7.6 m above mean sea level) during Kharif season. The date of sowing for the first year was 19th June 2020 and for the second year, 16th June 2021 using cowpea as the host crop following a Randomized Block Design (RBD)having three replications for each treatment with a 3.0m × 4.0 m plot size. In each replication, the number of plots was seven. Therefore, each field experiment consisted of 21 plots, with row-to-row and plant-to-plant spacing of 30 cm and 15 cm, respectively.

The two most potential strains of Bacillus (B-11 and PR-19) against Rhizoctonia were applied solely or in combination with Pseudomonas (GP-8) to check whether their bipartite interaction may improve the bioefficacy or not. Seeds were treated with Bacillus subtilis based formulation alone (B-11 or PR-19) or in combination (B-11+PR-19, B-11+GP-8, PR-19+GP-8) @ 5g/kg of cowpea seeds before sowing. Seeds were placed in a capped plastic container, prevailing minimum moisture condition, followed by a rotary motion for homogenous distribution of bacterial cells surrounding the seed coat. The bacterial-mixed seed was kept for 5-6 hours before sowing.  Sowing of the treated seeds was done followed by soil drenching by the prepared formulations @ 5 g/L of water at 10 days after the sowing of seeds. The treatments of the field experiments were (i) Bacillus sp. –based bioformulation-I (PR-19), (ii) Bacillus sp. –based bioformulation-II (B-11), (iii) Two Bacillus sp.–based bioformulation (B-11+PR-19), (iv) Bacillus sp. and Pseudomonas sp.–based bioformulation-I (B-11+GP-8), (v) Bacillus sp. and Pseudomonas sp.–based bioformulation-II (PR-19+GP-8), (vi) Carbendazim 50% WP, and (vii) Control.

Standard agronomic practices like manure and fertilizer application, hand weeding, and need-based irrigation were followed as and when required. Two prophylactic sprays with  Imidacloprid ( 17.8% SL) @ 1 mL/ 3 L of water were done uniformly at 30 and 60 days after sowing (DAS)in all the plots to protect the crop against different sucking insect pests of cowpea, while Chloropyriphos  20% EC @2.5 mL/L was used against different leaf-cutting insects as and when required. The disease severity of web blight of cowpea (R. solani) was recorded at 50 DAS.

Statistical analysis. SPSS statistical software was used to analyze all the components of the present work. Randomized Block Design (RBD) with three replications per treatment was used in the case of the field experiments. For comparing the treatment means, the least significant difference (LSD) test was used at the p<0.05 level.

Efficacy of prepared PGPR-based bioformulations on the plant growth characteristics of cowpea (cv. Kashi Kanchan)

Effect on plant height, root length, and shoot-root ratio of cowpea 

Plant height. Results obtained from the field trial conducted in 2020 (Table 1) revealed that the maximum plant height was recorded in the combination of bacterial bioagents B-11 + GP-8 (Bacillus sp.+Pseudomonas sp.) (21.20 cm), followed by PR-19 + GP-8 (Bacillus sp. + Pseudomonas sp.) (20.37 cm) in comparison to the control (15.27cm) when the observation was recorded at 30 DAS. Other bacterial isolates, like B-11 (20.12 cm), B-11+PR-19 (19.10 cm), and PR-19 (18.62 cm), also exhibited significant plant height increases over control. When plant heights were recorded at 60 DAS, a similar trend was recorded in different treatments, and these were B-11 + GP-8 (31.23 cm), PR-19+GP-8 (29.87 cm), B-11 (28.42 cm), B-11 + PR-19 (27.77cm), PR-19 (26.63 cm), and carbendazim (23.50 cm) over the control treatment (18.03 cm) (Table 1).

Experimental results obtained from the field trial conducted in 2021 showed a similar effect on the plant height of cowpeas obtained at 30 DAS and 60 DAS (Table 1). At 30 DAS, maximum plant height (22.90 cm) was recorded in treatment B-11 + GP-8 (Bacillus sp. + Pseudomonas sp.), followed by 21.10 cm in PR-19 + GP-8 (Bacillus sp. + Pseudomonas sp.), and  20.20 cm in B-11(Bacillus sp.)  in comparison to control (15.03 cm) and standard fungicidal check (16.23 cm). Bacillus sp. (PR-19) alone and in combination with another Bacillus sp. (B-11) also showed significant plant heights of cowpea (18.30 cm and 18.77 cm) in contrast to the control and standard fungicidal checks. Data recorded for cowpea plant height at 60 DAS also exhibited a similar trend.  These were 34.27 cm in B-11 + GP-8 (Bacillus sp. +Pseudomonas sp.), 32.23 cm in PR-19 + GP-8  (Bacillus sp. +Pseudomonas sp.), 29.57 cm in B-11 (Bacillus sp.), 28.53cm in B-11+PR-19 (Bacillus sp. + Bacillus sp.), and 26.90 cm in PR-19 (Bacillus sp.), which were significantly higher than control (21.23 cm) and standard fungicidal check (23.37 cm), respectively.

Root length. The root length of cowpea was recorded at 30 and 60 DAS from both the experimental trials conducted in the years 2020 and 2021. The field trial conducted in 2020 showed maximum root length at 60 DAS and was recorded from the treatment B-11 + GP-8 (Bacillus sp.+ Pseudomonas sp.) (20.41 cm), followed by PR-19 + GP-8 (Bacillus sp. + Pseudomonas sp.) (19.54 cm), and in B-11 (Bacillus sp.) (18.22 cm) in comparison to control (13.97 cm) and standard fungicidal check (15.33 cm). Bacillus sp. (PR-19) alone (16.77 cm) and in combination with another Bacillus sp. (B-11+PR-19) (17.51 cm) also showed significantly higher root length in contrast to the control and standard fungicidal check (Table 1).

A similar trend of effect by the bacterial isolates on the root growth of cowpeas was recorded in the field trial conducted in 2021. Results (Table 1) revealed that treatment (B-11 + GP-8) showed maximum root length, followed by PR-19 + GP-8, B-11, B-11+PR-19, and PR-19 in comparison to the control and standard fungicidal check at both 30 and 60 DAS.  

Shoot: Root ratio. The shoot-root ratio of the cowpea plant was recorded at 30 and 60 DAS from both the experimental trials conducted in 2020 and 2021, which showed no significant difference among the treatments (Table 1). The shoot-root ratio varied from 1.76 to 2.48 at 30 DAS and 1.30 to 1.67 at 60 DAS in the field trial conducted in 2020, while it was recorded to be 2.03-2.30 at 30 DAS and 1.52-1.77 in 2021.

Effect of prepared PGPR-based bioformulations on the number of branches, leaves, and nodules per plant of cowpea (cv. Kashi Kanchan) 

Number of branches per plant. A significant difference among the different treatments was observed in the number of branches, leaves, and nodules of the cowpea crop at different time intervals when crops were imposed with bacterial bioagents and standard fungicide at two locations. Results from the field trial conducted in 2020 (Fig 2) recorded the highest number of branches per plant in B-11+GP-8 (5.88 & 6.73), followed by PR-19 + GP-8 (5.11 & 6.00), and by B-11(4.78 & 5.74) in comparison to fungicide (3.85 & 4.96), and control treatment (3.22 & 4.66) at 30 and 60 DAS, respectively. 

Results obtained from the field trial conducted in 2021 (Fig. 3) also showed a similar trend in the number of branches per plant. The number of branches per plant was highest in theB-11+GP-8 treatment (5.78 and 6.70), followed by PR-19+ GP-8 (5.29 and 6.00), and  B-11 (4.64 and 5.66) in comparison to the fungicide check (3.78 and 4.92) and control treatments  (3.04 and 4.74) at 30 and 60 DAS, respectively. 

Number of leaves per plant. Results obtained from the field trial conducted in 2020 (Fig. 2) showed the highest number of leaves per plant by the combination of inoculation with B-11+GP-8 (20.33 and 25.33), followed by PR-19+ GP-8 (19.33 and 23.67), and by B-11(18.33 and 22.33) in comparison to fungicide check (15.33 and 18.33) and control treatment (13.33 and 16.33) at 30 and 60 DAS, respectively.

Results from the field trial conducted in 2021 (Fig. 3) also revealed a significant increase in leaf number per plant in different treatments, with the highest nominal value in B-11+GP-8 (21.00 and 26.00), followed by PR-19+ GP-8 (20.67 and 24.00), and B-11 (19.00 and 23.00) in comparison to the fungicide check (16.00 and 19.00) and control (14.00 and 17.00) treatments at 30 and 60 DAS, respectively. 

Number of nodules per plant. The effect of different rhizobacteria on nodulation in cowpeas was recorded from both experimental fields at 50 DAS, and results obtained from the field trial conducted in 2020 (Fig. 2) showed a significant increase in nodule number in different treatments over control. Maximum nodules per plant were obtained in plants treated with bacteria B-11+GP-8 (31.33), followed by PR-19 + GP-8(30.33), and B-11 (29.00) in comparison to fungicide check (20.00) and control treatment (19.67). A combination of bacteria B-11 + PR-19 (27.33) and PR-19 (26.67) also showed increased nodule numbers per plant over fungicide check and control.

Results from the field trial conducted in 2021, presented in (Fig. 3) showed a similar trend in the nodulation of cowpea. The nodule numbers per plant as recorded were B-11+GP-8 (32.67) followed by PR-19+GP-8(31.33), B-11 (29.67), PR-19 (28.33), and B-11+PR-19 (26.33) in comparison to fungicide check (21.67) and control (24.33). 

Effect of prepared PGPR-based bioformulations on pod number and yield of cowpea (cv. Kashi Kanchan) 

Results obtained from the field trial conducted in 2020 (Table 2) revealed that maximum pods per plant (26.33), yield (10.22 t/ha), and percent increase of yield over control (45.17%)  were recorded in the bioagent consortia of B-11 + GP-8, which were followed by consortia of PR-19 + GP-8 (number of pods/plant: 25.67; yield: 10.04 t/ha; percent increased of yield over control: 42.61%)  and by B-11 (number of pods per plant: 23.67; yield: 9.63 t/ha; percent increased of yield over control:  36.89%), significantly higher than the test chemical fungicide treatment (number of pods per plant: 19.33;yield: 8.33 t/ha; percent increase of yield over control: 18.32 %). The lowest number of pods/plant (16.67) and yield (7.04 t/ha) were recorded in the control treatment. 

Results from the field trial conducted in 2021 (Table 2) showed a similar trend in pod number per plant, total yield, and percent increment of yield over the control treatment. Among the different bioagents and their consortia, maximum pods per plant (21.52), yield (9.25t/ha), and percent increase of yield  (48.95 %)  over control were recorded in the bioagents consortia of B-11+GP-8,  followed by consortia of PR-19+ GP-8 (number of pods/plant: 20.26; yield: 8.78 t/ha; percent increase of yield over control: 41.38 %),  and by B-11 (number of pods/plant: 19.04; yield: 8.32 t/ha; percent increase of yield over control: 33.98 %), which were significantly higher than the test chemical fungicide treatment (number of pods/plant: 17.15; yield: 7.99 t/ha; percent increase of yield over control: 28.66 %). The lowest pods/plant (15.67) and yield (6.21 t/ha) were recorded in the control treatment. 

Effect of prepared PGPR-based bioformulations on web blight disease incidence in cowpea (cv. Kashi Kanchan) under field conditions. Results obtained from the field trial conducted in 2020 (Table 3) showed that inoculation with Bacillus spp. (B-11 and PR-19) alone or in combination with Pseudomonas sp. (GP-8) significantly reduced the web blight disease severity in comparison to the control. The data revealed that minimum disease severity (16.66%) was recorded in fungicide (Carbendazim 50% WP)-treated plots and gave maximum disease control (52.84%). Among the treatments with bioagents and their combinations, B-11+GP-8 exhibited the lowest disease severity (20.59%) and highest disease reduction (41.72%) of web blight, followed by PR-19+ GP-8 (21.07% & 40.36%), B-11+PR-19 (23.03% & 34.81%), B-11 (24.04% & 31.95%), and PR-19 (26.07% & 26.21%) with comparison to the disease severity of control treatment.

A similar trend of disease severity was recorded for web blight disease conducted in 2021. Results (Table 3) showed that all the treatments significantly reduced the disease severity of web blight over untreated control. Treatment with the test fungicide Carbendazim-50% WP exhibited minimum severity (20.11%), while treatments with bacterial formulations (B-11+GP-8), (B-11+PR-19), (PR-19 + GP-8), B-11, and PR-19 showed significantly reduced disease severity, viz., 26.18%, 26.67%, 27.82%, 28.89%, and 30.07%, respectively, over the disease severity of the untreated control (47.85%). The percent disease control of web blight was also recorded as highest when treatment was imposed with carbendazim (57.97%). This was followed by treatments with other bacterial formulations like B-11+GP-8 (45.29%), B-11+PR-19 (44.26%), PR-19+ GP-8 (41.86%), B-11 (39.62%), and PR-19 (37.16%), respectively.

DISCUSSION

In the present experiment, three selected PGPR-based formulations viz., (PR-19- Bacillus sp.); B-11- Bacillus sp.; GP-8-Pseudomonas sp.) were explored alone or in combination as seed treatments and soil drenching on cowpea. Overall, B-11- Bacillus sp. + GP-8-Pseudomonas sp. showed promising results on different plant growth characteristics like plant height, root length, noodle number, pod yield, and total yield of cowpea. Other formulations also showed good potential in comparison to the control treatment. The efficacy of different bacterial formulations alone or in combinations showed also promising results in reducing disease severity against web blight of cowpea, but results were not reached to the level performed by the test chemical fungicide, carbendazim 50% WP. 

Cowpea web blight disease severity was found in plots treated with Bacillus sp. alone or in combinations as compared to the control in the present field studies, which indicated that seed treatment followed by soil drenching with bacterial antagonists leads to an increase in their population with time in the surrounding area of the seed, which protects them from attacks by different plant pathogens (Mitra et al., 2021). Bacterial bioagents normally require more time for the initial establishment to exert their efficacy against pathogens through the elicitation of ISR (Induced Systemic Resistance) mechanisms, especially by the B. subtilis strains for controlling plant diseases. Moreover, jasmonic acid (JA), ethylene, and the regulatory gene NPR1 are thought to be essential for the signal transduction pathways that B. subtilis activates in plants (Garcia-Gutierrez et al., 2013). These findings indicated that in the present study, the increased total yield of cowpea in the bacterial bioagent-treated plot over fungicide treatment might be due to the extended activity of the bioagent that protected the crop later in the crop phase and led to an enhancement of crop yield.

Several works on the management of soil-borne diseases through the application of bacterial antagonists have supported the present investigation of cowpea web blight management. For instance, the ability of B. subtilis IMP 215 to prevent the growth of carrot root infections while in storage was very promising. In conjunction with appropriate storage techniques, processing carrots with B. subtilis - IMP 215 was reported to be a helpful tool for minimizing microbial damage and minimizing losses (Pershakova et al., 2018). In another study, it was reported that the application of an indigenous B. subtilis strain showed promising natural biopesticide agents in cowpea crops, suppressing several soil-borne pathogens like F. verticilloides, F. equiseti, F. solani, F. oxysporum, and R. solani (Abaidoo et al., 2011).  

The enhancement of plant growth and productivity of crops in cowpeas in the present experiments might also be due to the secretion of some extracellular metabolites called siderophores by different bacterial formulations used. The presence of side rophore-producing PGPR in the rhizosphere increases the rate of Fe3+ supply to plants and therefore enhances the plant growth and productivity of crops (Mustafa et al., 2019). According to the current research, the growth promotion of crops using Bacillus sp. may also be a result of other factors, such as the production of phytohormone precursors like indole acetic acid (IAA-auxin), phosphate solubilization, siderophore production, and biocompatible species like nitrogen-fixing species like Azospirillum and Azotobacter in soils that increase the soil's fertility (Kashyap et al., 2019).  Bacillus sp. alone or in combination exhibited improved plant growth, possibly due to more nutrient uptake in plants and a synergistic interaction of Bacillus with other microbes in the plant root that promotes plant growth, mineral nutrition, and stress tolerance (Egamberdieva, 2016).

In the crop field, a variety of Bacillus and Paenibacillus species can support crop health in various ways. They can stimulate plant development by improving nutrient uptake through soil mineral mobilization, as well as by activating the host plant's defense mechanisms through ISR before infection (Kumar et al., 2011). In our study, Bacillus sp. (B-11)  and Pseudomonas sp. (GP-8)  and their consortia exhibited significantly taller plants, suggesting that direct length promotion might be due to cell elongation as an activity of ACC deaminase reduced ethylene levels in the plants and maximizing plant growth (Ji et al., 2020).

The production of various phytohormones and enzymes, such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, the mineralization of nutrients, such as nitrogen, phosphate, potassium, and zinc solubilization, nitrogen fixation, increased root absorption capacity, and the production of siderophores by Bacillus and Pseudomonas, may all contribute to the growth promotion and increased yield of cowpea in the current investigation (Chowdappa et al., 2013).

Enhanced pod number and increased yield of cowpeas as found in the present study are also evident by an experiment done earlier by Ahmad et al. (2019) that treatments by PGPR B. subtilis B4 gave highly dry weight and number of healthy pods and a higher increased yield percentage compared to control both in green house and open field environmental conditions.

Table 1: Efficacy of prepared PGPR-based bio formulations on plant height, root length, and shoot-root ratio of cowpea (cv. Kashi Kanchan) at field trial conducted in the year 2020 and 2021.

(PR-19= Bacillus sp.; B-11- Bacillus sp.; GP-8= Pseudomonas sp., DAS=Days after sowing)

Table 2: Efficacy of prepared PGPR-based bio formulations on pod number and yield of  cowpea (cv. Kashi Kanchan) at field trial conducted in the year 2020 and 2021.

(PR-19= Bacillus sp.; B-11- Bacillus sp.; GP-8= Pseudomonas sp., DAS=Days after sowing)

Table 3: Efficacy of prepared PGPR-based bioformulations against Web blight disease incidence of cowpea (cv. Kashi Kanchan) at field trial conducted in the year 2020 and 2021.

(PR-19= Bacillus sp.; B-11- Bacillus sp.; GP-8= Pseudomonas sp, ** Parenthesis within the brackets arc sine transformed value)

Fig. 1.  Web blight (R. solani) disease infected cowpea plant.

[PR-19= Bacillus sp.; B-11- Bacillus sp.; GP-8= Pseudomonas sp., DAS =Days after sowing

*Average of 3 replications]

Fig. 2. Efficacy of prepared PGPR-based bio formulations on number of branches, leaves, and nodules per plant of cowpea (cv. Kashi Kanchan) at Field study-I (2020).

[PR-19= Bacillus sp.; B-11- Bacillus sp.; GP-8= Pseudomonas sp., DAS =Days after sowing

*Average of 3 replications]

Fig. 3. Efficacy of prepared PGPR-based bio formulations on number of branches, leaves, and nodules per plant of cowpea  (cv. Kashi Kanchan) at Field study-II (2021).

1.                                     (b)

Fig.  4. Pods (a) and nodules (b) of a plant treated by B-11+GP-8 at 50 DAS.

Isolation and deployment of zone specific bioformulation for promotion of higher yield and suppression of disease have a potential for the sustainable development with low cost input, further study of plant and microbe’s metabolites can reveal the synergistic interaction between the host and PGPR’s and can give us a insight about the unknown interacting partners.