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Article

Plant Growth-Promoting Potential of Entomopathogenic Fungus Metarhizium pinghaense AAUBC-M26 under Elevated Salt Stress in Tomato

by
Priyanka J. Chaudhary
1,
Raghunandan B. L.
1,*,
Hiren K. Patel
2,
Punit V. Mehta
3,
Nainesh B. Patel
1,
Bandeppa Sonth
4,
Anand Dave
5,
Samadhan Y. Bagul
6,
Divya M.
7,
Devendra Jain
8,
Abdulaziz Abdullah Alsahli
9 and
Prashant Kaushik
10
1
AICRP on Biological Control of Crop Pests, Anand Agricultural University, Anand 388110, India
2
Department of Agricultural Microbiology, Anand Agricultural University, Anand 388110, India
3
Department of Soil Science and Agricultural Chemistry, Anand Agricultural University, Anand 388110, India
4
ICAR—Indian Institute of Rice Research, Hyderabad 500030, India
5
Department of Microbiology and Biotechnology Centre, The Maharaja Sayyajirao University of Baroda, Vadodara 390002, India
6
ICAR—Directorate of Medicinal and Aromatic Plants Research, Anand 387310, India
7
Department of Agricultural Microbiology, Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences, Shivamogga 577201, India
8
Department of Molecular Biology and Biotechnology, Maharana Pratap University of Agriculture and Technology, Udaipur 313001, India
9
Botany and Microbiology Department, Faculty of Science, King Saud University, Riyadh 11541, Saudi Arabia
10
Institute for the Conservation and Improvement of Valencian Agrodiversity, Technical University of Valencia, 46022 Valencia, Spain
*
Author to whom correspondence should be addressed.
Agronomy 2023, 13(6), 1577; https://doi.org/10.3390/agronomy13061577
Submission received: 29 April 2023 / Revised: 27 May 2023 / Accepted: 29 May 2023 / Published: 11 June 2023
(This article belongs to the Special Issue Innovative Biofertilizers: An Eco-Friendly Approach for Soil Improvement)
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Abstract

:
Entomopathogenic fungi Metarhizium species are generally employed to manage the soil-dwelling stage of insect pests, and are known for their rhizocompetency property. Since this fungus is typically recommended for use in soil, it could potentially be investigated as a bioinoculant to reduce abiotic stress, such as salinity, along with improved plant growth promotion. Salt stress tolerance potential of native Metarhizium isolates was evaluated based on mycelial fresh weight, dry weight, and spore yield. All the isolates were found to tolerate NaCl concentrations (50 mM, 100 mM, 150 mM, 200 mM, 250 mM, and 300 mM) supplemented in the culture medium. Metarhizium anisopliae (AAUBC-M15) and Metarhizium pinghaense (AAUBC-M26) were found to be effective at tolerating NaCl stress up to 200 mM NaCl. These two isolates were analyzed in vitro for plant growth-promoting traits at elevated salt concentrations (100 and 200 mM NaCl). No significant effect on IAA production was reported with the isolate M. pinghaense (AAUBC-M26) (39.16 µg/mL) or in combination with isolate M. anisopliae (AAUBC-M15) (40.17 µg/mL) at 100 mM NaCl (38.55 µg/mL). The salinity stress of 100 mM and 200 mM NaCl had a significant influence on the phosphate solubilization activity, except in the co-inoculation treatment at 100 mM NaCl. The isolates were positive for ACC deaminase enzyme activity. An increase in salt concentration was accompanied by a steady and significant increase in chitinase enzyme activity. Total phenolics (149.3 µg/mL) and flavonoids (79.20 µg/mL) were significantly higher in the culture filtrate of Metarhizium isolates at 100 mM NaCl, and gradual decline was documented at 200 mM NaCl. M. pinghaense (AAUBC-M26) proved to be promising in reducing the salt stress in tomato seedlings during the nursery stage. In the pot culture experiment, the treatment comprising soil application + seedling root dip + foliar spray resulted in improved growth parameters of the tomato plant under salt stress. This study shows that Metarhizium, a fungus well known for controlling biotic stress brought on by insect pests, can also help plants cope with abiotic stress, such as salinity.

1. Introduction

Entomopathogenic fungi commonly occur in soil, and can exist as rhizosphere colonizers and endophytes that provide benefits in agroecosystems. These benefits include plant growth promotion through nutrient transfers, and suppression of plant disease and insect pests [1,2,3]. Amongst the different entomopathogenic fungi, Metarhizium (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae) are well-adapted to soil in agricultural systems. Multiple species of Metarhizium are able to colonize the roots of many plant species, including switch grass, haricot bean, tomato, wheat, and soybean [4]. Several entomopathogenic fungi have the ability to colonize plant roots of monocot and dicot plants, transferring insect nitrogen derived from insect remains straight to the roots, establishing a mutualistic association. The endophytic colonization of entomopathogenic fungi stimulates the plant defense system and the production of secondary metabolites [5,6]. Compounds produced by the plant or the fungus can result in antibiosis. Some Metarhizium species, mainly Metarhizium robertsii, Metarhizium anisopliae, and Metarhizium pinghaense, are known to be strong root colonizers, and can show a vast range of applications in agriculture due to their important ecological roles in plant care, acting as bio-pesticides or as bio-fertilizers [7].
Soil salinity, being one of the most severe threats to global agricultural output, affects the production aspect of agriculture as well as microbial biodiversity in the soil. It is an edaphic stress that has impacted 45 million hectares of irrigated land out of 230 million hectares. Salinity causes annual losses of about USD 12 billion worldwide [8]. Even though different biotic and abiotic environmental factors greatly affect plant growth and yield, salt stress is still considered as one of the major stress factors that seriously inhibits plant growth and microbe survival in soil. Saline soils are widely distributed throughout the world and hinder crop growth and productivity. In India, salinity affects around 9.38 Mha, while the Gujarat state in particular has a major share of the saline-affected soil, accounting for approximately 2.23 Mha [9]. Therefore, overcoming the negative effects of salt stress in agriculture and ensuring global food security are critical issues. Climate change and human activities are causing global warming, which seriously hampers plant development.
Microorganisms that improve plant growth must be incorporated into agricultural practices. Association with microorganisms favors the survival of plants in the environment. Several plant-growth-promoting microbes such as Arthrobacter sp., Bacillus amyloliquefaciens, Bacillus subtilis, Burkholderia cepacia, Pseudomonas fluorescens, and Streptomyces sp. [10,11,12,13,14] are known to secrete a large array of secondary metabolites (Phenols, Flavonoids and Indole Acetic Acid (IAA), etc.) that facilitate crops under stress conditions. During stress, endophytic association accumulates and signals several secondary metabolites [15]. Isoflavones (IF), being phytoalexins, are accumulated in the plant to a certain level in order to mitigate stress of either a biotic or abiotic nature. Fungi also produce a significant number of secondary metabolites, including phytohormones (Auxins, Gibberellins, Cytokinins, and Abscisic Acid)and antifungal and antibacterial compounds [16]. Studies have shown that plants treated with a variety of symbiotic fungi are often healthier than untreated plants [17,18,19,20]. The various studies have documented plant growth promotion by soil fungi in different crop plants. However, there are only a few scientific studies pertaining to role of fungal entomopathogens/myco-insecticides in enhancing plant growth under stressful environmental conditions such as salinity [21]. Insect-pathogenic Metarhizium anisopliae is a well-known rhizocompetent fungus and an essential mycoinsecticide, which is typically employed for the control of the soil-dwelling stage of insect pests. This entomopathogenic fungus could be explored as a bioinoculant to alleviate abiotic stress such as salinity with enhanced plant growth promotion. Therefore, the potential of the entomopathogenic fungus Metarhizium species to alleviate salt stress and promote plant growth in the tomato crop was investigated.

2. Materials and Methods

2.1. Metarhizium Isolates

We used the native isolates of Metarhizium species (6 Nos.) viz., M. robertsii (AAUBC-M7), M. anisopliae (AAUBC-M15), M. anisopliae (AAUBC-M21), M. anisopliae (AAUBC-M22), M. pinghaense (AAUBC-M26), and M. robertsii (AAUBC-M27) maintained at the microbial culture repository of AICRP on Biological Control of Crop Pests, Anand Agricultural University (AAU), Anand (Gujarat) that had been previously identified and characterized using molecular methods [22] (Table 1). The isolates were sub-cultured on potato dextrose agar (PDA) (Hi-Media, Mumbai, India) plates and slants. The sub-cultured Petri plates and slants were incubated at 28 ± 1 °C for 8 days and then preserved at 4 °C until further use.

2.2. Screening of Metarhizium Isolates for Pathogenicity in Pupal Stage of Helicoverpa armigera

The insect culture of H. armigera reared and maintained at AICRP on Biological Control of Crop Pests, AAU, Anand (Gujarat) was used for insect pathogenicity studies. The immersion method was used for testing the pathogenicity of Metarhizium isolates as described by [23]. Spore suspension of Metarhizium isolates (1 × 108 conidia/mL) was prepared using 0.1% Tween 80 (Hi-Media, Mumbai, India) solution (v/v) and tested against pupae of H. armigera. Pupae, after immersion in fungal suspension, were individually released in plastic trays (4 × 3 × 3 cm/well—32 well type) composed of moistened autoclaved soil. In the control, the same amount of 0.1% Tween 80 (Hi-Media, Mumbai, India) solution (v/v) was used. Sixteen individuals were tested in each treatment and each treatment was replicated thrice. The trays were covered by ventilated plastic lids and incubated at 28 ± 1 °C and 65 ± 5% RH in a Biological Oxygen Demand (BOD) incubator. The pupal body’s black discoloration and subsequent fungus growth were signs that the Metarhizium species had infected it. Pupal mortality was observed daily up to 10 days, and cumulative pupal mortality (%) was calculated.

2.3. Screening of Metarhizium Isolates for Salt Tolerance

The screening of Metarhizium isolates for salt tolerance was carried out according to the protocol of [24]. The isolates were taken from PDA master plates and inoculated in 50 mL of each of Czapek-broth (Sucrose 30 g; Sodium nitrate 2 g; Dipotassium phosphate 1 g; Magnesium sulphate 0.5 g; Potassium chloride 0.5 g; Ferrous sulphate 0.01 g; Agar 15 g; Distilled water 1000 mL; pH 7.3 ± 0.2) and Potato Dextrose Broth (PDB) amended with different concentrations of NaCl viz., 50, 100, 150, 200, 250, and 300 mM. The flasks were incubated at 28 ± 1 °C for 10 days. Each treatment was replicated thrice. After 10 days of incubation, mycelial fresh weight (g), dry weight (g), and spore yield (No./mL) of the inoculated isolates was recorded.

2.4. Analysis of Plant-Growth-Promoting Traits of Metarhizium Isolates at Elevated NaCl Levels

The two Metarhizium isolates viz., M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26), demonstrating the highest insect pathogenicity and tolerance to elevated salt concentration were analyzed for different plant-growth-promoting traits under salt stress conditions. A salt concentration of 100 mM and 200 mM NaCl was amended in the culture medium of the fungus while analyzing the different parameters. The treatment without NaCl amendment served as the control treatment. Based on the observations of salt stress tolerance, the isolate M. robertsii (AAUBC-M27) was utilized as a salt-susceptible isolate. There were twelve treatment combinations (T1—AAUBC-M27; T2—AAUBC-M15; T3—AAUBC-M26; T4—Consortium/Co-inoculation of AAUBC-15 and AAUBC-M26; T5—AAUBC-M27+100 mM NaCl; T6—AAUBC-M15+100 mM NaCl; T7—AAUBC-M26+100 mM NaCl; T8—Consortium/Co-inoculation of AAUBC-15 and AAUBC-M26+100 mM NaCl; T9—AAUBC-M27+200 mM NaCl; T10—AAUBC-M15+200 mM NaCl; T11—AAUBC-M26+200 mM NaCl; T12—Consortium/Co-inoculation of AAUBC-15 and AAUBC-M26+200 mM NaCl) and three replications were maintained for each treatment.

2.5. Indole Acetic Acid (IAA) Production

The production of IAA by the Metarhizium isolates (M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) was quantitatively estimated following the protocol of [25]. Fifty mL of potato dextrose broth (PDB) (Hi-Media, Mumbai, India) amended with 0.1% L-tryptophan (Hi-Media, Mumbai, India) (w/v) was inoculated with an agar plug (5 mm) obtained from a 14-days-old culture of Metarhizium isolate grown on potato dextrose agar (PDA) (Hi-Media, Mumbai, India), and was incubated for 14 days at 28 ± 1 °C. Five mL of the culture filtrate was centrifuged at 10,000 rpm for 5 min, and one mL of the clear supernatant taken into test tubes was allowed to react with 2 mL of Salkowski reagent (Perchloric acid (35%) 50 mL; FeCl3 (0.5 M) 1 mL) [26] in the dark for 30 min. Development of a pink red color in the medium indicated IAA production by the fungus. The IAA was quantified by reading the color intensity at 530 nm in a UV–Vis spectrophotometer (Beckman Coulter DU730, Beckman Coulter, Krefeld, Germany), and the amount of IAA released was calculated from a standard graph prepared using known quantities of pure IAA (Merck, Rahway, NJ, USA) (100–1000 µg/mL).

2.6. Phosphate Solubilization Activity (Agar Plate Assay)

The method described by [27] was used to check phosphate solubilization activity of Metarhizium isolates. Metarhizium isolates were spot inoculated on Pikovskaya’s agar medium (Yeast extract 0.5 g; Dextrose 10 g; Calcium phosphate 5 g; Ammonium sulphate 0.5 g; Potassium chloride 0.2 g; Magnesium sulphate 0.1 g; Manganese sulphate 0.0001 g; Ferrous sulphate 0.0001 g; Agar 15 g; Distilled water 1000 mL) comprising calcium phosphate as fixed phosphate, and incubated for seven days at 28 ± 1 °C. The zone of clearance around the fungal colony was observed and the solubilization index was calculated.
S o l u b i l i z a t i o n   i n d e x = T o t a l   d i a m e t e r c o l o n y + h a l o   z o n e ( m m ) D i a m e t e r   o f   t h e   f u n g a l   c o l o n y   ( m m )

2.7. Phosphate Solubilization Activity (Broth Assay)

The phosphate solubilization ability of Metarhizium isolates was checked using the vanado-molybdate method [28]. One mL (109 spores/mL) inoculum of Metarhizium isolates were inoculated to 100 mL of Pikovskaya’s broth. Inoculated flasks were incubated for seven days at 28 ± 1 °C. Further, 9 mL clear suspension was taken from broth in a test tube. One mL of trichloric acetic acid was added to the tube and centrifuged at 3000 rpm for 30 min. The aliquot (0.5 mL) was taken from the supernatant in tubes and 2 mL of vanado-molybdate reagent was added. The volume was made up to 10 mL and tubes were incubated at room temperature for 30 min. Absorbance was measured at 420 nm using a UV–Vis spectrophotometer (Beckman Coulter DU730). For standard, 100 ppm solution of KH2PO4 was prepared and different aliquots of standard solution viz., 10–50 ppm were taken and 2 mL of vanado-molybdate reagent was added. The remaining procedure was the same as described above. The graph of absorbance versus concentration of phosphate in μg was plotted for the standard and samples were compared to calculate phosphate concentration (μg/mL).

2.8. Potash Solubilization Activity

The Metarhizium isolates were screened for potassium-solubilizing activity on Aleksandrov agar medium (Magnesium sulphate 5 g; Calcium carbonate 0.1 g; Potassium alumino silicate 2 g; Dextrose 5 g; Ferric chloride 0.005 g; Calcium phosphate 2.0 g; Agar 20 g; pH 7.2 ± 0.2; Distilled water 1000 mL) using the spot plate method [29]. The fungal growth disc (5 mm) was placed on the center of a Petri plate and then was incubated at 28 ± 1 °C. After 7 days of incubation, the zone of potash solubilization was checked.

2.9. ACC Deaminase Production

The Metarhizium isolates were tested for ACC deaminase enzyme production based on their ability to use ACC (1-Aminocyclopropane-1-carboxylate) as a sole nitrogen source in the minimal medium. Cultures were inoculated on Petri plates containing minimal DF (Dworkin and Foster) salts medium supplemented with 3 mM ACC substrate (Merck, Rahway, NJ, USA). The plates were incubated for 7 days at 28 ± 1 °C. The growth of the fungus (mm) was recorded on the 7th day of incubation. Isolates growing on ACC-amended plates were considered as ACC deaminase enzyme producers [30].

2.10. Chitinase Production

Chitinase production by Metarhizium isolates was assessed using a chitin degradation index by measuring the clear zone produced by the degradation of chitin. The culture media suggested by [31] was used for the study ((NH4)2SO4 3 g, KH2PO4 2 g, MgSO4 0.3 g, citric acid 1 g, colloidal chitin (Sigma-Aldrich, St. Louis, MO, USA) 4.5 g, agar 15 g, distilled water 1000 mL, pH 4.8, supplemented with 0.15 g of bromocresol purple). The fungal growth disc (5 mm) from the five-day-old fungal culture was inoculated at the center of the Petri plate and was incubated at 28 ± 1 °C. The diameter of both the fungal colony and orange colored chitin degradation halo zone was measured at 7 days after inoculation (DAI). The Chitin Degradation Index (CDI) was calculated as follows,
C D I = D i a m e t e r   o f   h a l o   z o n e   o f   d e g r a d a t i o n   ( m m ) D i a m e t e r   o f   f u n g a l   c o l o n y   ( m m )

2.11. Quantification of Total Phenolics in the Culture Filtrate of Metarhizium Isolates

The total phenolics was determined by following the method of [32]. One mL culture filtrate of the fungus was extracted with 80% ethanol after putting it on a shaker for 30 min. The resultant extract (0.5 mL) was mixed with Folin–Ciocalteau reagent (0.5 mL) and 10% Na2CO3 (0.5 mL). The absorbance of the reaction mixture was measured at 760 nm using a UV–Vis spectrophotometer (Beckman Coulter DU730) after 1 h of incubation at room temperature. Gallic acid (Sigma-Aldrich, USA) concentrations ranging from 10 to 300 μg/mL were prepared and a calibration curve was obtained using a linear fit. The phenol content in the fungal extracts was derived from the standard curve and expressed as μg of gallic acid eq. per mL of extract.

2.12. Quantification of Total Flavonoids in the Culture Filtrate of Metarhizium Isolates

Colorimetric determination of flavonoids was carried out by following the protocol of [33]. One mL of culture filtrate was mixed with 4 mL of distilled water and 0.3 mL of sodium nitrite solution (5%) (w/v); 0.3 mL of aluminum chloride solution (10%) was then added to the mixture, followed by the addition of 0.2 mL of NaOH (1 M) after 1 min. The volume was made up to 10 mL with distilled water and the contents were mixed thoroughly. A white milky coloration indicated the presence of flavonoids and absorbance was measured at 510 nm (Beckman Coulter DU730). Quercetin (Sigma-Aldrich, USA) concentrations ranging from 10 to 800 μg/mL were prepared and a standard calibration curve was obtained using a linear fit. The flavonoid content in the fungal extracts was derived from the standard curve and expressed as μg of quercetin eq. per mL of fungal extract.

2.13. Solid-State Fermentation of Metarhizium Isolates

The mass multiplication of Metarhizium isolates viz., M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26), was carried out using the solid-state fermentation method using sorghum grains. Half-broken sorghum grains (100 g) were taken in a polypropylene bag (26 × 16 cm) and 40 mL water was added to maintain the moisture level at 40%. The bags were closed with cotton plugs and sterilized at 121 ± 2 °C for 30 min. After cooling, the lumps of grains in the bags were broken and later inoculated with 5 mL of spore suspension (1 × 108 conidia/mL) of Metarhizium isolates. The inoculated bags were incubated at 28 ± 1 °C for 14 days. Fungal mass was harvested along with the substrate and air-dried. After drying, the spore mass along with grain carrier (1 g) was suspended in 25 mL sterile 0.1% Tween-80 (Hi-Media, Mumbai, India) solution (v/v) and gently vortexed. The spores of Metarhizium were observed and counted using Neubauer’s chamber under a microscope (40×) (Olympus CX43).

2.14. Plant-Growth-Promoting and Salt-Stress-Alleviating Potential of Metarhizium Isolates in Tomato during Nursery Stage

The effect of salt stress and inoculation with Metarhizium isolates viz., M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26), on tomato seed germination and seedling growth was studied. Potting mixture comprising equal proportions of cocopeat and vermicompost (Mfr: Hygienic Enterprises, Anand, India) was prepared. Sterilized potting mixture was used as a growth medium to fill the pot trays. In the case of treatments comprising Metarhizium isolates, 10 mL of spore suspension (1 × 108 conidia/mL) was enriched in 100 g sterilized potting mixture for seven days and then added in pot trays. The concentration of 50 mM NaCl with an EC value of almost 5 dS/m was used to induce salt stress. In the study, tomato cultivar AT-3, a determinate type variety, noted to be sensitive to salinity stress and developed by Main Vegetable Research Station (MVRS) of Anand Agricultural University, Anand, India, was utilized. One day before sowing, salinity stress was induced by adding 50 mM NaCl solution to the pot trays (100 mL/pot tray) receiving salt stress (treated control) and salt stress + Metarhizium treatments. The treatment receiving Metarhizium species alone was maintained for each isolate under study. There were a total of six treatments and each was repeated four times. Two seeds were sown per pith of the pot tray (40 well type—5 × 4 × 4 cm). Germination percentage was recorded in each treatment. Further, seedling height (cm), fresh weight (g), and dry weight (g) of seedlings was recorded in 25-days-old seedlings. Vigour index was calculated by using the formula VI = plant height × germination % [34].

2.15. Quantification of Biochemical and Physiological Parameters in Tomato Plants during Nursery Stage

The biochemical parameters associated with salinity tolerance were analyzed in the tomato seedlings. The fresh leaf samples were collected from 25-days-old seedlings and analyzed for total phenolics [32], total flavonoids [33], and total proline content.

Quantification of Total Proline

The proline content was measured according to the method described by [35]. The fresh leaf samples (0.5 g) were homogenized in 4 mL of aqueous sulfosalicylic acid (3%) and the homogenate was subjected to centrifugation at 12,000 rpm for 10 min. Equal volumes of glacial acetic acid and ninhydrin were added to the supernatant. The mixture was boiled in a water bath adjusted at 100 °C for 1 h and then extraction was carried out with 4 mL of toluene. The absorbance was measured at 520 nm using a UV–Vis spectrophotometer (Beckman Coulter DU730, Germany), using toluene as a blank. A standard graph was plotted by using different concentrations (2, 4, 6, 8, 10 μg/mL) of proline (Sigma-Aldrich, USA).

2.16. Histology of Tomato Seedlings Root in Nursery Stage

Microscopic examination of changes in anatomical features of root tissue was observed following the protocol of [36]. Hand-cut sections of fresh root materials parallel to different treatments (Untreated Control, Treated control (50 mM NaCl), M. pinghaense (AAUBC-M26) + 50 mM NaCl, M. pinghaense (AAUBC-M26)) were allowed to soak in distilled water for 2–3 min. The staining solution was prepared using 0.05% toluidine blue in 0.1 M phosphate buffer of pH 6.8. These sections were immersed in a staining solution for 1 min. Following staining, sections were washed with tap water and examined at 10× and 40× using a research microscope (Olympus CX43, Tokyo, Japan). The root samples were analyzed for the root anatomy, number, and thickness of xylem cells.

2.17. Plant Growth-Promoting and Salt-Stress-Alleviating Potential of Metarhizium Species in Tomato under Pot Culture Conditions

The isolate M. pinghaense (AAUBC-26), found to be effective in in vitro and nursery stage experiments, was used in the pot culture studies. The 25-days-old seedlings of tomato cultivar AT-3 were transplanted from pot trays into the main pot (45 cm diameter and 25 kg soil holding capacity) containing sandy loam soil (pH (1:2.5) 7.85; EC (1:2.5)–0.82 dS/m; Organic carbon 0.97%; Available Nitrogen 235.20 kg/ha; Available P2O5 38.45 kg/ha; Available K2O 189.50 kg/ha) as the growth medium. While transplanting, the recommended dose of FYM (N:P:K 0.82:0.52:0.75 %) and chemical fertilizers (KRIBHCO, India) were incorporated in each pot (FYM 150 g/pot; N:P2O5:K2O (kg/ha) 37.5:37.5:37.5 as basal application and N:P2O5:K2O (kg/ha) 37.5:00:00 through top dressing at 40 days after transplanting).
One day before transplanting, salinity stress was induced by adding water containing 50 mM NaCl to the pots (500 mL/pot). Later, after a week of transplanting, water containing 50 mM NaCl was applied two times at five-day intervals. The spore suspension of M. pinghaense (AAUBC-M26) was treated to the plants through different methods and their combinations as described below. The experiment was laid out in a completely randomized design with four replications for each treatment. In each pot, four plants were maintained during the experiment period.
In the treatments of seedling root dip, seedling roots were dipped in spore suspension of 20 mL/L water (1 × 108 conidia/mL) for 30 min before transplanting. In case of soil application, 10 mL spore suspension (1 × 108 conidia/mL) was enriched in 100 g soil for seven days, and then it was incorporated in the pot soil while transplanting. For foliar treatments, 5 mL spore suspension (1 × 108 conidia/mL)/L of water was sprayed on the plant foliage using a hand-held garden sprayer. The first spray was carried out 7 days after transplanting. Subsequent sprays were carried out at 7-day intervals, and a total of three sprays were taken up during the experiment period. The plants were watered using tap water (pH 6.8) as and when required. The experiment was terminated at 60 days after transplanting. Observations on plant height (cm), shoot and root length (cm), and fresh and dry weights of shoot and root (g) were documented. The EC and pH of soil samples were recorded at the time of harvesting (soil:water 1:2.5) using the method described by [37].

2.18. Statistical Analysis

The data obtained on different aspects were subjected to ANOVA. The treatment means were compared by using Duncan’s Multiple Range Test (DMRT) in SPSS (version 20).

3. Results

3.1. Pathogenicity of Metarhizium Isolates in Pupal Stage of H. armigera

The Metarhizium isolates tested against pupal stage of H. armigera showed varied pupal mortality (Figure 1). The highest pupal mortality of 82.05% was observed in the isolate M. pinghaense (AAUBC-M26), which was statistically on a par with the pupal mortality showed by the isolate M. anisopliae (AAUBC-M15) (79.19%). The isolate M. anisopliae (AAUBC-M22) showed the lowest pupal mortality (65.17%).

3.2. Salinity Stress Tolerance of Metarhizium Isolates

The growth response of various Metarhizium isolates at different NaCl concentrations (50 mM, 100 mM, 150 mM, 200 mM, 250 mM, and 300 mM) amended in Czapeck broth and potato dextrose broth has been recorded in the form the mycelial fresh weight (g), dry weight (g), and spore yield. All the isolates under examination were found to be tolerant to the NaCl concentrations supplemented. In case of fungal growth in Czapeck broth, mycelial fresh weight was gradually increased at either 50 mM or 100 mM NaCl concentration and a gradual decline was noticed. The Metarhizium isolates M. pinghaense (AAUBC-M26) (2.02 g) and M. anisopliae (AAUBC-15) (2.01 g) recorded the highest mycelial fresh weight at 100 mM NaCl concentration. There was a considerable decline in mycelial fresh weight at higher NaCl concentrations. The lowest fresh weight was recorded at 300 mM NaCl treatment. Concerning the dry weight of Metarhizium isolates, a similar pattern was registered as witnessed in fresh weight observations. The highest mycelial dry weights were reported for the isolates M. pinghaense (AAUBC-M26) (0.30 g) and M. anisopliae (AAUBC-15) (0.29 g) at 100 mM NaCl. Furthermore, among all the isolates, the lowest dry weight of the mycelium was recorded at 300 mM NaCl (0.15 g) by isolates M. robertsii (AAUBC-M7), M. anisopliae (AAUBC-M22), and M. robertsii (AAUBC-M27) (Figure 2) (supplementary material). A similar pattern of fungal growth parameters was recorded in potato dextrose broth (Figure 3). The highest spore yield was documented in Czapeck broth as compared to potato dextrose broth (PDB). Spore yield was gradually increased at either 100 mM or 150 mM NaCl concentration, and a subsequent gradual decline was noticed (Figure 2 and Figure 3).

3.3. Plant-Growth-Stimulating Traits at Elevated Salt Stress

3.3.1. IAA Production

The Metarhizium isolates under study were tested for IAA production, which was shown to be present in all three Metarhizium isolates (Figure 4). Higher concentrations of NaCl resulted in less IAA being synthesized. The treatment T4 containing the co-inoculation of isolates M. anisopliae (AABU-M15) and M. pinghaense (AAUBC-M26) without NaCl addition recorded the highest amount of IAA (40.17 µg/mL). Among the two isolates, M. pinghaense (AAUBC-M26) showed the highest IAA production (39.16 µg/mL). The salt-susceptible Metarhizium isolate M. robertsii (AAUBC-M27) showed the IAA production of 32.23 µg/mL. When the culture medium was amended with higher NaCl concentrations (100 and 200 mM), IAA production was subsequently reduced. At the 100 mM NaCl level, treatment T8 M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) showed an IAA production of 38.55 µg/mL, which was followed by the treatment T7 M. pinghaense (AAUBC-M26) (37.58 µg/mL). This finding demonstrates the effectiveness of Metarhizium isolate M. pinghaense (AAUBA-M26) alone and in combination with isolate M. anisopliae (AAUBC-M15) in tolerating the salt stress of 100 mM NaCl, which has no significant effect on IAA production. Furthermore, the salt-susceptible isolate T5 M. robertsii (AAUBC-M27) recorded the lowest IAA (31.13 µg/mL) at 100 mM NaCl. Concerning the response of isolates at 200 mM NaCl, treatment T12 combination of isolates M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) exhibited the highest IAA production (37.67 µg/mL). The other treatments comprising the sole isolates viz., T9 M. robertsii (AAUBC-M27) (26.89 µg/mL) T10 M. anisopliae (AAUBC-M15) (27.72 µg/mL), and T11 M. pinghaense (AAUBA-M26) (30.16 µg/mL), witnessed the significant decline in the production of IAA. Amongst all the treatments, the lowest IAA production was recorded in the salt-sensitive Metarhizium isolate T9 M. robertsii (AAUBC-M27) at 200 mM NaCl (26.89 µg/mL).

3.3.2. Phosphate and Potash Solubilization

The Metarhizium isolates were found to have different degrees of phosphate solubilization. A clear zone of phosphate solubilization was noticed on the Pikovskaya’s agar medium supplemented with different NaCl levels (Figure 5). The phosphate solubilization efficiency (SE) was calculated and expressed as solubilization index (SI) (Supplementary Materials). The highest solubilization index was found in the treatment T4—co-inoculation of isolates M. pinghaense (AAUBC-M26) and M. anisopliae (AAUBC-M15) (2.12)—which was followed by the treatments T3 M. pinghaense (AAUBC-M26) (2.08) and T2 M. anisopliae (AAUBC-M15) (1.98), in which no salt stress was induced. The lowest solubilization index was documented in M. robertsii (AAUBC-M27) (1.92). At 200 mM NaCl concentration, a significant decrease in solubilization index of T11—M. pinghaense (AAUBC-M26) (1.74), T10—M. anisopliae (AAUBC-M15) (1.69) and T12—Consortium (1.83) was noticed. Further, a broth assay was performed using Pikovskaya’s broth supplemented with tri-calcium phosphate to study the efficacy of Metarhizium isolates in releasing inorganic phosphate (Figure 4). The observations reported during the broth assay are in line with the findings of the agar plate assay. Salinity stress of 100 mM and 200 mM NaCl had a significant influence on the phosphate solubilization activity of the isolates except in the treatment T8 constituting the isolates M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) with 100 mM NaCl (78.7 µg/mL). A significant decline in the phosphate concentration was realized at the elevated NaCl level of 200 mM. No apparent zone of potash solubilization was observed with Metarhizium isolates inoculated on Aleksandrov agar medium. However, a medium-to-light growth of isolates was recorded on the plates. All the three isolates of Metarhizium (AAUBC-M15, AAUBC-M26 and AAUBC-M27) showed medium, loose mycelial growth with no supplementation of NaCl. The plates with elevated levels of NaCl (100 and 200 mM) showed light and loose mycelial growth.

3.3.3. ACC-Deaminase and Chitinase Enzyme Activity

Metarhizium isolates showed dense mycelial growth on the Petri plates containing (NH4)2SO4 as the sole nitrogen source. Very poor mycelial growth was noticed on the plates amended with nitrogen-free DF salts, whereas the plates containing ACC as the sole source of nitrogen without salt stress demonstrated the dense growth of Metarhizium isolates. However, plates supplemented with ACC + 100 mM NaCl showed medium growth of isolates, whereas at 200 mM NaCl, light growth of isolates was documented. The chitin degradation index (CDI) was used to express the chitinase enzyme’s activity. The higher NaCl concentrations had a significant impact on the chitinase enzyme activity. A gradual and substantial increase in chitinase enzyme activity was seen with an increase in salt concentration. Among the treatments where NaCl was not added, the treatment T4 comprising co-inoculation of isolates M. anisopliae (AAUBC-15) and M. pinghaense (AAUBC-26) showed a CDI of 1.96. It was noted that a slight increase in CDI of various treatments at 200 mM NaCl as compared to CDI of treatments supplemented with 100 mM NaCl (Figure 6) (Supplementary Materials).

3.3.4. Phenolics and Flavonoids Production

The biochemical constituents phenolics and flavonoids as antioxidants are important to promote stress tolerance in plants. Production of phenolics and flavonoids by Metarhizium fungus indicates its ability to provide protection against stress conditions. An increase in phenolics and flavonoids content in the culture filtrate was documented with an increase in NaCl concentration up to 100 mM. Later, there was substantial decline at 200 mM NaCl (Figure 7). Significantly, the highest phenolics content was recorded in the treatment T8 comprising the co-inoculation, i.e., M. anisopliae (AAUBC-15) and M. pinghaense (AAUBC-26) with 100 mM NaCl (149.3 µg/mL). The lowest phenolics content was recorded in the treatment T1 comprising salt-susceptible Metarhizium isolate M. robertsii (AAUBC-M27) (112.7 µg/mL) without NaCl supplementation. Similar findings were observed regarding flavonoids production. The treatment T8 registered significantly higher flavonoids content (79.2 µg/mL). The treatment T1 with M. robertsii (AAUBC-M27) without NaCl supplementation recorded the lowest flavonoids in the culture filtrate (60.3 µg/mL). Further, it was also noted that the interaction effect between distinct Metarhizium isolates at various NaCl levels tested for the various plant-growth-promoting characteristics mentioned above was found to be statistically insignificant.

3.4. Growth Promotion in Tomato Plant by Metarhizium Species under Salt Stress

During the nursey stage, the isolates M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) were evaluated for reducing salt stress in tomato in relation to plant growth. The highest seed germination percentage was observed in the treatment inoculated with the isolate M. pinghaense (AAUBC-M26) followed by M. anisopliae (AAUBC-M15). The treatments comprising Metarhizium + salinity stress (50 mM NaCl) showed a higher germination rate than the control treatment (50 mM NaCl). The potential of Metarhizium fungus in reducing salt stress is apparently demonstrated by this finding. Similar results were observed on the growth parameters, such as seedling height, vigor index, and fresh and dry weight of seedlings (Table 2 and Figure 8). Treatment containing the isolate M. pinghaense (AAUBC-M26) proved to be more promising than the treatments inoculated with M. anisopliae (AAUBC-M15). Furthermore, phenolics, flavonoids, and proline content in tomato leaves was estimated. The phenolics and flavonoids content was decreased under salt stress, whereas the osmolyte proline content increased with the salt stress (Figure 9). However, in treatments of Metarhizium isolate + salt stress (50 mM NaCl), an increase in phenolics and flavonoids content was realized. These results showed that the Metarhizium fungus could reduce salt stress by increasing the production of biochemical components necessary for plants to tolerate salinity stress. Various anatomical changes were observed in the root tissues of tomato seedlings in various treatments of salt stress and M. pinghaense (AAUBC-M26) inoculation (Figure 10). Plants treated with fungus showed an increase in thickness of the endodermis compared to plants grown in salt stress of 50 mM NaCl. The root sections of un-inoculated plants demonstrated the normal growth of endodermis and xylem cells, whereas the root tissues of the plants treated with 50 mM NaCl showed a very thin endodermis with poorly developed xylem tissue. Plants treated with 50 mM NaCl and M. pinghaense (AAUBC-M26) showed a greater number of thickened xylem cells and endodermis. The root anatomy of plants treated with M. pinghaense (AAUBC-M26) alone showed a greater number of xylem cells with enhanced cell thickness. These observations indicate the salt-stress-mitigating potential of Metarhizium fungus. Additionally, at NaCl concentrations (0, 50 mM), the interaction effect between the two Metarhizium isolates (AAUBC-M15 and AAUBC-M26) examined for the numerous plant growth-promoting traits indicated above was shown to be statistically not significant.
The pot culture experiment was conducted to determine the effectiveness of M. pinghaense (AAUBC-M26) in reducing salt stress on tomato plants. The spore suspension of M. pinghaense (AAUBC-M26) was treated through soil application, seedling root dip, and foliar spray. The treatment comprising soil application + seedling root dip + foliar spray resulted in improved plant growth parameters viz., plant height, root length, and fresh and dry weight of shoot and root (Figure 11, Figure 12 and Figure 13). At the completion of the experiment, soil samples in each treatment were analyzed for EC and pH. The values of EC and pH documented were found to be non-significant (Supplementary Materials). However, pH was reduced in the treatments inoculated with Metarhizium because of the ability of the fungus to produce organic acids. Metarhizium species is a well-known fungus for regulating biotic stress of insect pests in crop plants, and this study reveals that it can also aid plants in coping with abiotic stress such as salinity.

4. Discussion

Metarhizium sp., an entomopathogenic fungus, plays multifarious roles in the agro-ecosystem. In addition to its primary use as a mycoinsecticide for the sustainable management of a variety of insect pests, it also has the potential to function as a bio-inoculant to encourage plant growth and development under stressful conditions [4,7]. In the present study, an attempt has been made to study salt-stress-alleviating potential and plant growth promotion of native isolates of entomopathogenic fungus Metarhizium species in tomato. In a nutshell, our data demonstrates the potential of native entomopathogenic fungus M. pinghaense AAUBC-M26 in reducing the salt stress and enhancing the plant growth attributes in tomato. Initially, we checked the pathogenicity potential of all the isolates against the pupal stage of H. armigera. The entomopatogenic fungus Metarhizium is rhizocompetent and widely known for its efficacy against the soil-dwelling stage of various insect pests [38,39]. M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) showed the highest pupal mortality. Further, all the isolates were screened for salt stress tolerance at different concentrations of NaCl. By recording the highest mycelial fresh weight, dry weight, and spore yield, M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) were found to be highly competent at tolerating NaCl stress. Numerous endophytic beneficial fungi have been investigated as potential plant growth promoters in both natural and stressed conditions [1,40,41]. Jan et al. [42] reported the salt-tolerating potential of endophytic fungus Meyerozyma carribbica isolated from Solanum xanthocarpum. The strain SXSp1 was most resistant against salt stress of 100, 150, and 200 mM NaCl supplemented in growth media. The possible explanation for salt stress tolerance is that M. caribbica produces reductone, which might have reacted with the free radicals and blocked radical chain reactions. Similarly, [43] reported the salt tolerance of endophytic fungus Aspergillus ochraceus able to tolerate 200 g sodium chloride/L. They explained that the reason behind this is that fungi mandate passive mechanisms such as the production of extracellular polysaccharides to cover the cells or increase the thickness of the cell wall, and the creation of cell clumps to survive at high salt concentrations.
Many soil microorganisms are able to synthesize auxin, mainly Indole 3-Acetic Acid (IAA), to influence the growth of plants [15,16]. IAA production was observed in the Metarhizium isolates. The highest IAA production was recorded in the co-inoculation treatment of isolates without NaCl addition. IAA production was subsequently reduced at NaCl concentrations used. IAA-producing microbes are believed to improve root growth and increase root length, resulting in an increased root surface area, thus enabling increased access to soil-based nutrients and affecting biosynthesis of various metabolites in the plant [44,45]. IAA production by M. robertsii was described for the first time in [46], which facilitated plant growth in an Arabidopsis system. This phenomenon supported the significance of auxin in Metarhizium’s capacity to promote plant growth. Siqueira et al. [47] reported the ability of Brazilian isolates of Metarhizium to produce IAA in vitro higher than Trichoderma harzianum isolates. Our study reveals that at higher NaCl concentrations, IAA production was reduced. However, observations of the isolate M. pinghaense (AAUBC-M26) alone and in combination with isolate M. pinghaense (AAUBC-M26) tolerating salt stress of 100 mM NaCl, with no tangible effect on IAA production, warrants further investigation.
Phosphorus is an essential element for plants, because it is the least available of all essential nutrients in soil [44]; the release of insoluble forms of phosphorus is an important aspect of PGP microorganisms method for increasing soil phosphorus availability. Soil microorganisms can solubilize insoluble phosphorus by producing organic exudates, organic acids, acid phosphatases, or enzymes, such as phytases, making P available to be acquired by plants [48]. We documented the phosphate solubilization activity of Metarhizium isolates. The treatment constituting co-inoculation of M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26) without NaCl addition was found to be superior. However, the salinity stress of 100 mM and 200 mM NaCl had significantly affected phosphate solubilization activity except in the co-inoculation treatment at 100 mM NaCl. The decreased phosphate solubilization with an increase in NaCl concentration might be due to detrimental effects of NaCl on the phosphatase enzyme or on generation of organic acids by Metarhizium isolates. Siqueira et al. [47] reported phosphate solubilization indices of T. harzianum, M. humberi, M. robertsii, and M. anisopliae ranging from 1.16 to 2.12. The two Metarhizium isolates viz., M. humberi and M. anisopliae performed better in phosphate solubilization than T. harzianum. Regarding the solubilization of potash by Metarhizium isolates inoculated on Aleksandrov agar medium, no apparent zone of potash solubilization was observed. However, a medium-to-light growth of isolates was recorded on the plates. The chemical interaction between Aleksandrov medium components and NaCl might have inhibited Metarhizium isolates from developing normally.
Salt stress inhibits the activity of ACC deaminase enzyme, as evidenced by the growth characteristics of Metarhizium isolates on the ACC-containing medium supplemented with or without NaCl. Plants can employ the ACC deaminase to combat abiotic constraints such as salinity stress. It promotes plant growth and development under stress conditions by lowering ethylene levels in the plant. The ability of beneficial fungal isolates to produce the enzyme ACC deaminase helps plants to tolerate biotic and abiotic stress when used as plant probiotics. The higher NaCl concentrations had a significant influence on chitinase enzyme activity. During the study, a gradual and substantial increase in chitinase enzyme activity was registered with an increase in salt concentration. An increase in CDI (Chitin Degradation Index) of various treatments at 200 mM NaCl was documented as compared to the CDI of treatments supplemented with 100 mM NaCl. A significant number of fungi produces chitinases, which may aid in promoting plant growth directly and indirectly. However, the role of chitinases in salt stress tolerance and plant growth promotion by Metarhizium is not clearly understood. Generally, this group of enzymes has been explored in the context of biocontrol of phytopathogens and nematodes [49]. The enhanced chitinase enzyme activity exhibited by Gujarat (India) isolates of Metarhizium may be a novel characteristic in selection of good entomopathogenic fungus with multifarious attributes for both biotic and abiotic stress management. Chitin production by Metarhizium was also reported by [47]. harzianum has stronger chitinase activity than the other three fungi M. robertsii, M. anisopliae, and M. humberi. The M. robertsii isolate was the second-best chitinase producer, followed by M. anisopliae and M. humberi.
We registered the production of phenolics and flavonoids in the culture filtrate of Metarhizium isolates. There was significantly higher phenolics and flavonoids contents at 100 mM NaCl. Plants produce higher quantities of phenolics to protect them from unfavorable condition. Phenolics are accumulated by higher plants during biotic and abiotic stresses to undergo normal growth. Flavonoids are antioxidant compounds crucial for fostering plant development in stressful conditions. This can be the reason that inoculated fungus supports plants to produce more phenolics and flavonoids in order to detoxify reactive oxygen species (ROS) that might have generated at elevated salt stress. Hamayun et al. [50] found similar findings regarding the fungus Aspergillus flavus producing phenolics and flavonoids in culture filtrates. Our report appears to be the first report documenting the phenolics and flavonoids in a culture filtrate of Metarhizium species.
Generally, the tomato plant is believed to be salt-sensitive. In the present study, we found that inoculating plants with Metarhizium species significantly enhanced the growth attributes such as seedling height, vigor index, and fresh and dry weight of seedlings during nursery stage. M. pinghaense (AAUBC-M26) proved to be more promising than M. anisopliae (AAUBC-M15). This finding is consistent with related research employing Metarhizium on plant growth attributes of 35-days-old tomato seedlings [51]. The plants under salt stress realized the reduced phenolics and flavonoids, whereas the osmolyte proline content was pronounced. However, in treatments of Metarhizium isolate + salt stress (50 mM NaCl), an increase in phenolics and flavonoids content was observed. By enhancing the production of the biochemical elements required for plants to endure salinity stress, this study demonstrated that the Metarhizium fungus may minimize salt stress. The osmolyte proline accumulation is a crucial process in maintaining the osmotic balance while the plant is experiencing stressful conditions [52]. The results of enhanced accumulation of proline in the plants inoculated with plant-growth-promoting fungus under salinity stress are in agreement with the findings of [42]. Moreover, the stimulation of proline biosynthesis accounts for the increased amount of proline content in plants under salt stress [53]. In addition, tomato plants treated with Metarhizium species had a thicker root epidermis and improved xylem tissue compared to control treatments. Dave and Ingle [54] demonstrated the PGPR Streptomyces-9-mediated increase in the thickness of epidermis of pigeon pea roots and xylem tissue. The effectiveness of M. pinghaense (AAUBC-M26) was tested in a pot culture experiment to help tomato plants cope with salt stress. The spore suspension of M. pinghaense (AAUBC-M26) treated using soil application, seedling root dipping, and foliar spray increased the growth parameters of the plant, such as plant height, root length, and fresh and dried shoot and root weight. Supporting the results of this study, [21] reported that, in the presence of fungal Metarhizium anisopliae strain while exposed to salt stress (70 and 140 mM), the soybean plants showed significantly higher shoot length and shoot fresh and dry weight in comparison with the control. Plants respond to hyper-ionic and hyper-osmotic states, as well as dehydration, when exposed to salt over an extended period of time. Fungal symbioses have been found to reprogram physiological systems and enhance plant tolerance to stress under these conditions. It maintains the ionic homeostasis of the Na+:K+ ratio in plants. Endophytic-induced interplay of strigolactones play regulatory roles in salt tolerance by interacting with phytohormones [40]. The results of pot culture experiments highlight the plant growth promotion potential of M. pinghaense (AAUBC-M26) in tomato under saline environment.

5. Conclusions

Among six different Metarhizium isolates screened for salt stress tolerance, the isolates M. anisopliae AAUBC-15 and M. pinghaense AAUBC-M26 were found to be the most successful at withstanding the salt stress (up to 300 mM NaCl), having the highest mycelial fresh and dry weight along with highest spore yield. These isolates showed the plant-growth-promoting attributes at elevated salt stress levels (up to 200 mM NaCl). M. pinghaense AAUBC-M26 was found to be promising in alleviating salinity stress (up to 50 mM NaCl) in tomato plants during nursery and pot culture conditions. This study showed that M. pinghaense, a well known fungus used to regulate biotic stress caused by insect pests, can also help plants adapt to abiotic stress such as salinity. Researchers studying microbial biostimulants/bioinoculants in relation to various biotic and abiotic stresses will find the current findings to be helpful. Further investigations on molecular insights of the processes involved in tolerating the salt stress will pave the way to explore entomopathogenic fungus M. pinghaense as a novel bioinoculant with diverse mode of action, supporting plant growth to a larger extent.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy13061577/s1, Table S1. Growth response of Metarhizium isolates in Czapek broth amended with NaCl. Table S2. Growth response of Metarhizium isolates in potato dextrose broth amended with NaCl. Table S3. Spore yield of Metarhizium isolates in Czapek broth and potato dextrose broth amended with NaCl. Table S4. Phosphate solubilization activity and chitin degradation index of Metarhizium isolates. Table S5. Summary of Metarhizium isolates activity at different levels of NaCl. Table S6. EC and pH parameters of soil at harvesting.

Author Contributions

P.J.C.: Conceptualization, Methodology, Investigation, Validation, Original draft preparation; R.B.L.: Conceptualization, Validation, Writing—Review and editing, Supervision; H.K.P.: Writing—review and editing, supervision, resources; P.V.M.: Writing—review and editing, supervision; N.B.P.: Resources, visualization; B.S.: Resources, visualization; A.D.: Resources, visualization; S.Y.B.: Software, visualization; D.M.: Software, visualization; D.J.: Software, visualization; A.A.A.: Software, visualization; P.K.: Software, visualization. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The contributing author can provide the data that support the study’s findings upon reasonable request.

Acknowledgments

The authors would like to extend their sincere appreciation to the Researchers Supporting Project Number (RSP2023R236), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be considered as a potential conflict of interest.

Nomenclature

Treatments
T1Seedling root dip
T2Soil application
T3Foliar spray
T4Seedling root dip + Soil application
T5Seedling root dip + Foliar spray
T6Soil application + Foliar spray
T7Seedling root dip + Soil application + Foliar spray
T8Treated control (Salt stress)
T9Untreated control (No salt stress)

References

  1. Elena, G.J.; Beatriz, P.J.; Alejandro, P.; Lecuona, R.E. Metarhizium anisopliae (Metschnikoff) Sorokin promotes growth and has endophytic activity in tomato Plants. Adv. Biol. Res. 2011, 5, 22–27. [Google Scholar]
  2. Liao, X.; O’Brien, T.R.; Fang, W.; St Leger, R.J. The plant beneficial effects of Metarhizium species correlate with their association with roots. Appl. Microbiol. Biotechnol. 2014, 98, 7089–7096. [Google Scholar] [CrossRef] [PubMed]
  3. Barelli, L.; Moreira, C.C.; Bidochka, M.J. Initial stages of endophytic colonization by Metarhizium involves rhizoplane colonization. Microbiology 2018, 164, 1531–1540. [Google Scholar] [CrossRef] [PubMed]
  4. Bidochka, M.J.; Kamp, A.M.; Lavender, T.M.; Dekoning, J.; De Croos, J.A. Habitat association in two genetic groups of the insect-pathogenic fungus Metarhizium anisopliae: Uncovering cryptic species? Appl. Environ. Microbiol. 2001, 67, 1335–1342. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Agbessenou, A.; Akutse, K.S.; Yusuf, A.A.; Ekesi, S.; Subramanian, S.; Khamis, F.M. Endophytic fungi protect tomato and nightshade plants against Tuta absoluta (Lepidoptera: Gelechiidae) through a hidden friendship and cryptic battle. Sci. Rep. 2020, 10, 22195. [Google Scholar] [CrossRef] [PubMed]
  6. Hu, S.; Bidochka, M.J. Root colonization by endophytic insect-pathogenic fungi. J. Appl. Microbiol. 2021, 130, 570–581. [Google Scholar] [CrossRef] [PubMed]
  7. Ahmad, I.; Jiménez-Gasco, M.D.M.; Luthe, D.S.; Barbercheck, M.E. Systemic colonization by Metarhizium robertsii enhances cover crop growth. J. Fungi 2020, 6, 64. [Google Scholar] [CrossRef]
  8. FAO. Salt-Affected Soils; (Online); FAO: Rome, Italy, 2020. [Google Scholar]
  9. Srivastava, P.; Wu, Q.S.; Giri, B. Salinity: An overview. In Microorganisms in Saline Environments: Strategies and Functions; Giri, B., Varma, A., Eds.; Springer Nature: Cham, Switzerland, 2019; pp. 3–18. [Google Scholar] [CrossRef]
  10. Chauhan, P.S.; Lata, C.; Tiwari, S.; Chauhan, A.S.; Mishra, S.K.; Agrawal, L.; Agrawal, L.; Chakrabarty, D.; Nautiyal, C.S. Transcriptional alterations reveal Bacillus amyloliquefaciens-rice cooperation under salt stress. Sci. Rep. 2019, 9, 11912. [Google Scholar] [CrossRef] [Green Version]
  11. Upadhyay, S.K.; Singh, J.S.; Saxena, A.K.; Singh, D.P. Impact of PGPR inoculation on growth and antioxidant status of wheat under saline conditions. Plant Biol. 2012, 14, 605–611. [Google Scholar] [CrossRef]
  12. Ansari, F.A.; Ahmad, I.; Pichtel, J. Growth stimulation and alleviation of salinity stress to wheat by the biofilm forming Bacillus pumilus strain FAB10. Appl. Soil Ecol. 2019, 143, 45–54. [Google Scholar] [CrossRef]
  13. Kang, S.M.; Khan, A.L.; Waqas, M.; You, Y.H.; Kim, J.H.; Kim, J.G.; Hamayun, M.; Lee, I.J. Plant growth-promoting rhizobacteria reduce adverse effects of salinity and osmotic stress by regulating phytohormones and antioxidants in Cucumis sativus. J. Plant Interact. 2014, 9, 673–682. [Google Scholar] [CrossRef] [Green Version]
  14. Palaniyandi, S.A.; Damodharan, K.; Yang, S.H.; Suh, J.W. Streptomyces sp. strain PGPA39 alleviates salt stress and promotes growth of ‘Micro Tom’ tomato plants. J. Appl. Microbiol. 2014, 117, 766–773. [Google Scholar] [PubMed]
  15. Schultz, B.; Boyle, C. The endophytic continuum. Mycol. Res. 2005, 109, 661–686. [Google Scholar]
  16. Rai, M.; Rathod, D.; Agarkar, G.; Dar, M.; Brestic, M.; Pastore, G.M.; Junior, M.R.M. Fungal growth promotor endophytes: A pragmatic approach towards sustainable food and agriculture. Symbiosis 2014, 62, 63–79. [Google Scholar] [CrossRef]
  17. Strobel, G.; Daisy, B. Bioprospecting for microbial endophytes and their natural products. Microbiol. Mol. Biol. Rev. 2003, 67, 491–502. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  18. Hyde, K.D.; Soytong, K. The fungal endophyte dilemma. Fungal Divers. 2008, 33, e173. [Google Scholar]
  19. Khan, S.A.; Hamayun, M.; Yoon, H.; Kim, H.Y.; Suh, S.J.; Hwang, S.K.; Kim, J.M.; Lee, I.J.; Choo, L.Y.; Yoon, U.H.; et al. Plant growth promotion and Penicillium citrinum. BMC Microbiol. 2008, 8, 231. [Google Scholar] [CrossRef] [Green Version]
  20. Colla, G.; Rouphael, Y.; Di Mattia, E.; El-Nakhel, C.; Cardarelli, M. Co-inoculation of Glomus intraradices and Trichoderma atroviride acts as a biostimulant to promote growth, yield and nutrient uptake of vegetable crops. J. Sci. Food Agri. 2015, 95, 1706–1715. [Google Scholar] [CrossRef]
  21. Khan, A.L.; Hamayun, M.; Khan, S.A.; Kang, S.M.; Shinwari, Z.K.; Kamran, M.; Rehman, S.; Kim, J.G.; Lee, I.J. Pure culture of Metarhizium anisopliae LHL07 reprograms soybean to higher growth and mitigates salt stress. World J. Microbiol. Biotechnol. 2011, 28, 1483–1494. [Google Scholar] [CrossRef]
  22. Luz, C.; Rocha, L.F.N.; Montalva, C.; Souza, D.A.; Botelho, B.R.Z.; Lopes, R.B.; Faria, M.; Junior, I.D. Metarhizium humberi sp. nov. (Hypocreales: Clavicipitaceae), a new member of the PARB clade in the Metarhizium anisopliae complex from Latin America. J. Invertebr. Pathol. 2019, 166, 107216. [Google Scholar] [CrossRef]
  23. Goettel, M.S.; Inglis, G.D. Fungi: Hyphomycetes. In Manual of Techniques in Insect Pathology; Academic Press: Lacey, WA, USA, 1997; pp. 213–249. [Google Scholar] [CrossRef]
  24. Porcel, R.; Aroca, R.; Ruiz-Lozano, J.M. Salinity stress alleviation using arbuscular mycorrhizal fungi. A review. Agron. Sustain. Develop. 2012, 32, 181–200. [Google Scholar] [CrossRef] [Green Version]
  25. Patten, C.L.; Glick, B.R. Bacterial biosynthesis of indole-3-acetic acid. Can. J. Microbiol. 1996, 42, 207–220. [Google Scholar] [CrossRef] [PubMed]
  26. Gordon, S.A.; Weber, R.P. Colorimetric estimation of indole acetic acid. Plant Physiol. 1951, 26, 192. [Google Scholar] [CrossRef] [Green Version]
  27. El-Azouni, I.M. Effect of phosphate solubilizing fungi on growth and nutrient uptake of soybean (Glycine max L.) plants. J. Appl. Sci. Res. 2008, 4, 592–598. [Google Scholar]
  28. APHA. Standard Methods for the Examination of Water and Waste Water, 21st ed.; American Public Health Association: Washington, DC, USA, 2005. [Google Scholar]
  29. Hu, X.; Chen, J.; Guo, J. Two phosphate and potassium solubilizing bacteria isolated from Tianmu Mountain, Zhejiang, China. World J. Microbiol. Biotech. 2006, 22, 983–990. [Google Scholar] [CrossRef]
  30. Duan, J.; Müller, K.M.; Charles, T.C.; Vesely, S.; Glick, B.R. 1-aminocyclopropane-1-carboxylate (ACC) deaminase genes in Rhizobia from southern Saskatchewan. Microb. Ecol. 2009, 57, 423–436. [Google Scholar] [CrossRef]
  31. Agrawal, T.; Kotasthane, A.S. Chitinolytic assay of indigenous Trichoderma isolates collected from different geographical locations of Chhattisgarh in Central India. SpringerPlus 2012, 1, 73. [Google Scholar] [CrossRef] [Green Version]
  32. Qawasmeh, A.; Obied, H.K.; Raman, A.; Wheatley, W. Influence of fungal endophyte infection on phenolic content and antioxidant activity in grasses: Interaction between Lolium perenne and different strains of Neotyphodium lolii. J. Agric. Food Chem. 2012, 60, 3381–3388. [Google Scholar] [CrossRef]
  33. Srinivasan, K.; Jagadish, L.K.; Shenbhagaraman, R.; Muthumary, J. Antioxidant activity of endophytic fungus Phyllosticta sp. isolated from Guazuma tomentosa. J. Phytol. Phytochem. 2010, 2, 37–41. [Google Scholar]
  34. Abdul-Baki, A.A.; Anderson, J.D. Vigor determination in soybean seed by multiple criteria. Crop Sci. 1973, 13, 630. [Google Scholar] [CrossRef]
  35. Shaw, J.J.; Spakowicz, D.J.; Dalal, R.S.; Davis, J.H.; Lehr, N.A.; Dunican, B.F.; Orellana, E.A.; Narvaez-Trujillo, A.; Strobel, S.A. Biosynthesis and genomic analysis of medium-chain hydrocarbon production by the endophytic fungal isolate Nigrograna mackinnonii E5202H. Appl. Microbiol. Biotech. 2018, 99, 3715–3728. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  36. O’Brien, T.; Feder, N.; McCully, M.E. Polychromatic staining of plant cell walls by toluidine blue O. Protoplasma 1964, 59, 368–373. [Google Scholar] [CrossRef]
  37. Jackson, M.L. Soil Chemical Analysis; Prentic Hall Idia Pvt. Ltd.: New Delhi, India, 1973. [Google Scholar]
  38. Tahir, M.; Wakil, W.; Ali, A.; Sahi, S.T. Pathogenicity of Beauveria bassiana and Metarhizium anisopliae isolates against larvae of the polyphagous pest Helicoverpa armigera. Entomol. Gen. 2018, 38, 225–242. [Google Scholar] [CrossRef]
  39. Ramanujam, B.; Hosamani, A.; Poornesha, B.; Sowmya, E. Biological control of white grubs, Holotrichia serrata (Fabricius) in sugarcane by two species of entomopathogenic fungi, Metarhizium anisopliae and Beauveria bassiana. Int. J. Trop. Insect. Sci. 2021, 41, 671–680. [Google Scholar] [CrossRef]
  40. Gupta, S.; Schillaci, M.; Walker, R.; Smith, P.M.; Watt, M.; Roessner, U. Alleviation of salinity stress in plants by endophytic plant-fungal symbiosis: Current knowledge, perspectives and future directions. Plant Soil 2021, 461, 219–244. [Google Scholar] [CrossRef]
  41. Klinsukon, C.; Lumyong, S.; Kuyper, T.W.; Boonlue, S. Colonization by arbuscular mycorrhizal fungi improves salinity tolerance of eucalyptus (Eucalyptus camaldulensis) seedlings. Sci. Rep. 2021, 11, 1–10. [Google Scholar] [CrossRef]
  42. Jan, F.G.; Hamayun, M.; Hussain, A.; Iqbal, A.; Jan, G.; Khan, S.A.; Khan, H.; Lee, I.J. A promising growth promoting Meyerozyma caribbica from Solanum xanthocarpum alleviated stress in maize plants. Biosci. Rep. 2019, 39, BSR20190290. [Google Scholar] [CrossRef] [Green Version]
  43. Badawy, A.A.; Alotaibi, M.O.; Abdelaziz, A.M.; Osman, M.S.; Khalil, A.M.; Saleh, A.M.; Mohammed, E.F.; Hashem, A.H. Enhancement of seawater stress tolerance in barley by the endophytic fungus Aspergillus ochraceus. Metabolites 2021, 11, 428. [Google Scholar] [CrossRef]
  44. Fu, S.F.; Sun, P.F.; Lu, H.Y.; Wei, J.Y.; Xiao, H.S.; Fang, W.T.; Cheng, B.Y.; Chou, J.Y. Plant growth-promoting traits of yeasts isolated from the phyllosphere and rhizosphere of Drosera spatulata Lab. Fungal Biol. 2016, 120, 433–448. [Google Scholar] [CrossRef]
  45. Rana, K.L.; Kour, D.; Sheikh, I.; Yadav, N. Advances in Endophytic Fungal Research; Springer International Publishing: New York, NY, USA, 2019; Available online: https://www.springer.com/gp/book/9783030035884 (accessed on 29 March 2023).
  46. Liao, X.; Lovett, B.; Fang, W.; St Leger, R.J. Metarhizium robertsii produces indole-3-acetic acid, which promotes root growth in Arabidopsis and enhances virulence to insects. Microbiology 2017, 163, 980–991. [Google Scholar] [CrossRef]
  47. Siqueira, A.C.O.; Mascarin, G.M.; Gonçalves, C.R.; Marcon, J.; Quecine, M.C.; Figueira, A.; Delalibera, Í., Jr. Multi-trait biochemical features of Metarhizium species and their activities that stimulate the growth of tomato plants. Front. Sustain. Food Syst. 2020, 4, 137. [Google Scholar] [CrossRef]
  48. Gouda, S.; Kerry, R.G.; Das, G.; Paramithiotis, S.; Shin, H.S.; Patra, J.K. Revitalization of plant growth promoting rhizobacteria for sustainable development in agriculture. Microbiol. Res. 2018, 206, 131–140. [Google Scholar] [CrossRef] [PubMed]
  49. Gan, Z.; Yang, J.; Tao, N.; Liang, L.; Mi, Q.; Li, J.; Zhang, K. Cloning of the gene Lecanicillium psalliotae chitinase Lpchi1 and identification of its potential role in the biocontrol of root-knot nematode Meloidogyne incognita. Appl. Microbiol. Biotechnol. 2007, 76, 1309–1317. [Google Scholar] [CrossRef] [PubMed]
  50. Hamayun, M.; Hussain, A.; Afzal Khan, S.; Iqbal, A.; Lee, I.J. Aspergillus flavus promoted the growth of soybean and sunflower seedlings at elevated temperature. BioMed Res. Int. 2019, 2019, 1295457. [Google Scholar] [CrossRef] [Green Version]
  51. Dutta, P.; Kaushik, H.; Bhawmick, P.; Puzari, K.C.; Hazarika, G.N. Metarhizium anisopliae as endophyte has the ability of plant growth enhancement. Int. J. Curr. Res. 2015, 7, 14300–14304. [Google Scholar]
  52. Lei, P.; Xu, Z.; Liang, J.; Luo, X.; Zhang, Y.; Feng, X. Poly (γ-glutamic acid) enhanced tolerance to salt stress by promoting proline accumulation in Brassica napus L. Plant Growth Regul. 2016, 78, 233. [Google Scholar] [CrossRef]
  53. Khan, M.N.; Siddiqui, M.H.; Mohammad, F.; Naeem, M.; Khan, M.M.A. Calcium chloride and gibberellic acid protect linseed (Linum usitatissimum L.) from NaCl stress by inducing antioxidative defence system and osmoprotectant accumulation. Acta Physiol. Planta. 2010, 32, 121. [Google Scholar] [CrossRef]
  54. Dave, A.; Ingle, S. Streptomyces sp. S-9 promotes plant growth and confers resistance in pigeon pea (Cajanus cajan) against Fusarium wilt. 3 Biotech 2021, 11, 459. [Google Scholar] [CrossRef]
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Figure 1. Efficacy of native Metarhizium isolates against pupal stage of Helicoverpa armigera. Data represent mean of three replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
Figure 1. Efficacy of native Metarhizium isolates against pupal stage of Helicoverpa armigera. Data represent mean of three replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
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Figure 2. Growth response of Metarhizium isolates (M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) in Czapek broth amended with NaCl represented by mycelial fresh weight (g), dry weight (g), and spore yield. Data represent mean of three replications.
Figure 2. Growth response of Metarhizium isolates (M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) in Czapek broth amended with NaCl represented by mycelial fresh weight (g), dry weight (g), and spore yield. Data represent mean of three replications.
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Figure 3. Growth response of Metarhizium isolates ((M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26)) in potato dextrose broth amended with NaCl represented by mycelial fresh weight (g), dry weight (g), and spore yield. Data represent mean of three replications.
Figure 3. Growth response of Metarhizium isolates ((M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26)) in potato dextrose broth amended with NaCl represented by mycelial fresh weight (g), dry weight (g), and spore yield. Data represent mean of three replications.
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Figure 4. IAA production and release of inorganic phosphate by Metarhizium isolates (M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) at 100 mM and 200 mM NaCl concentration. Data represent the mean of three replications with standard error. Means with letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05. * indicates the co-inoculation of two isolates viz., AABC-M15 and AAUBC-M26.
Figure 4. IAA production and release of inorganic phosphate by Metarhizium isolates (M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) at 100 mM and 200 mM NaCl concentration. Data represent the mean of three replications with standard error. Means with letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05. * indicates the co-inoculation of two isolates viz., AABC-M15 and AAUBC-M26.
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Figure 5. Phosphate solubilization activity of Metarhizium isolates on Pikovskaya’s agar medium supplemented with different NaCl levels. (1) M. anisopliae (AAUBC-M15); (2) M. pinghaense (AAUBC-M26). (A) Control; (B) 100 mM NaCl; (C) 200 mM NaCl. Arrow indicates the zone of phosphate solubilization.
Figure 5. Phosphate solubilization activity of Metarhizium isolates on Pikovskaya’s agar medium supplemented with different NaCl levels. (1) M. anisopliae (AAUBC-M15); (2) M. pinghaense (AAUBC-M26). (A) Control; (B) 100 mM NaCl; (C) 200 mM NaCl. Arrow indicates the zone of phosphate solubilization.
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Figure 6. (Top) Chitin degradation activity of Metarhizium isolates on medium containing colloidal chitin. (1) M. anisopliae (AAUBC-M15) (2) M. pinghaense (AAUBC-M26) (3) Co-inoculation of M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26). (Bottom) Enhanced chitinase enzyme activity at elevated salt stress 200 mM NaCl (Co-inoculation of M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26). Arrow indicates the halo of chitin degradation.
Figure 6. (Top) Chitin degradation activity of Metarhizium isolates on medium containing colloidal chitin. (1) M. anisopliae (AAUBC-M15) (2) M. pinghaense (AAUBC-M26) (3) Co-inoculation of M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26). (Bottom) Enhanced chitinase enzyme activity at elevated salt stress 200 mM NaCl (Co-inoculation of M. anisopliae (AAUBC-M15) and M. pinghaense (AAUBC-M26). Arrow indicates the halo of chitin degradation.
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Figure 7. Total phenolics and flavonoids in the culture filtrate of Metarhizium isolates (M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) at 100 mM and 200 mM NaCl concentration. Data represent mean of three replications with standard error. Means with letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05. * indicates the co-inoculation of two isolates viz., AABC-M15 and AAUBC-M26.
Figure 7. Total phenolics and flavonoids in the culture filtrate of Metarhizium isolates (M. robertsii AAUBC-27, M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) at 100 mM and 200 mM NaCl concentration. Data represent mean of three replications with standard error. Means with letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05. * indicates the co-inoculation of two isolates viz., AABC-M15 and AAUBC-M26.
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Figure 8. Effect of Metarhizium isolate AAUBC-M26 inoculation on growth attributes of 25-days-old tomato seedlings under salt stress (50 mM NaCl) in nursery stage.
Figure 8. Effect of Metarhizium isolate AAUBC-M26 inoculation on growth attributes of 25-days-old tomato seedlings under salt stress (50 mM NaCl) in nursery stage.
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Figure 9. Effect of Metarhizium isolates (M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) on phenolics, flavonoids, and proline content in tomato seedlings. Data represent mean of three replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
Figure 9. Effect of Metarhizium isolates (M. anisopliae AAUBC-15, M. pinghaense AAUBC-26) on phenolics, flavonoids, and proline content in tomato seedlings. Data represent mean of three replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
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Figure 10. Anatomical features of root tissues of tomato seedlings treated with M. pinghaense AAUBC-M26 observed under the microscope (40×). Arrow indicates the cell wall thickening in xylem cells. (A) Un-inoculated control; (B) Treated control (50 mM NaCl); (C) M. pinghaense AAUBC-M26 + 50 mM NaCl; (D) M. pinghaense AAUBC-M26. (E) Cell wall thickening in xylem cells of plants treated with M. pinghaense AAUBC-M26.
Figure 10. Anatomical features of root tissues of tomato seedlings treated with M. pinghaense AAUBC-M26 observed under the microscope (40×). Arrow indicates the cell wall thickening in xylem cells. (A) Un-inoculated control; (B) Treated control (50 mM NaCl); (C) M. pinghaense AAUBC-M26 + 50 mM NaCl; (D) M. pinghaense AAUBC-M26. (E) Cell wall thickening in xylem cells of plants treated with M. pinghaense AAUBC-M26.
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Figure 11. Effect of M. pinghaense (AAUBC-26) inoculation on plant height and root length of tomato seedlings in pot culture experiment. Data represent mean of four replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05, DATP—Days after transplanting.
Figure 11. Effect of M. pinghaense (AAUBC-26) inoculation on plant height and root length of tomato seedlings in pot culture experiment. Data represent mean of four replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05, DATP—Days after transplanting.
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Figure 12. Effect of M. pinghaense (AAUBC-26) inoculation on shoot fresh weight and dry weight of tomato seedlings in pot culture experiment. Data represent mean of four replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
Figure 12. Effect of M. pinghaense (AAUBC-26) inoculation on shoot fresh weight and dry weight of tomato seedlings in pot culture experiment. Data represent mean of four replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
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Figure 13. Effect of M. pinghaense (AAUBC-26) inoculation on root fresh weight and dry weight of tomato seedlings in pot culture experiment. Data represent mean of four replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
Figure 13. Effect of M. pinghaense (AAUBC-26) inoculation on root fresh weight and dry weight of tomato seedlings in pot culture experiment. Data represent mean of four replications with standard error. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
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Table
Table 1. Description of Metarhizium isolates used in the study.
Table 1. Description of Metarhizium isolates used in the study.
Metarhizium Species and Isolate CodeSource/Isolation MethodSource Location with GPS
Co-Ordinates		Date of Sampling
Metarhizium robertsii-
AAUBC-M7		Soil/Insect bait with Corcyra cephalonicaVillage: Mendarda, Dist: Junagadh, Gujarat (India)
(21.3209° N, 70.4412° E)		12 July 2020
Metarhizium anisopliae-
AAUBC-M15		Forest soil/Insect bait with Corcyra cephalonicaVillage: Hiranvel, Dist. GirSomnath, Gujarat (India)
(21.1398° N, 70.5100° E)		15 December 2020
Metarhizium anisopliae-
AAUBC-M21		Forest soil/Insect bait with Corcyra cephalonicaVillage: Hiranvel, Dist. GirSomnath, Gujarat (India)
(21.1398° N, 70.5100° E)		31 December 2020
Metarhizium anisopliae-
AAUBC-M22		Maize soil/Selective medium (PDAY)Village: Runaj, Dist. Anand, Gujarat (India)
(22.5025° N, 72.7009° E)		27 December 2019
Metarhizium pinghaense-
AAUBC-M26		Maize soil/Insect bait with Corcyra cephalonicaVillage: Jahangirpura, Dist. Anand, Gujarat (India)
(22.5288° N, 72.9828° E)		20 December 2019
Metarhizium robertsii-
AAUBC-M27		Cucumber soil/Selective medium (PDAY)Village: Bochasan, Dist. Anand, Gujarat (India)
(22.4097° N, 72.8416° E)		31 January 2019
Table
Table 2. Effect of Metarhizium species inoculation on growth attributes of tomato seedlings under salt stress in nursery stage. Each value represents the mean of four replications. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
Table 2. Effect of Metarhizium species inoculation on growth attributes of tomato seedlings under salt stress in nursery stage. Each value represents the mean of four replications. Means with the letter/letters in common are not significant by Duncan’s Multiple Range Test (DMRT); p < 0.05.
TreatmentsGermination Percentage (%)Plant Height (cm)Vigor
Index		Seedling Fresh Weight (g)Seedling Dry Weight (g)
T1Untreated control94.61 ab11.42 d1052.62 bc1.41 b0.55 c
T2Treated control (50 mM NaCl)79.75 d8.25 e666.51 d1.10 c0.49 d
T3M. anisopliae
(AAUBC-M15) + 50 mM NaCl		87.89 bc16.07 c1410.49 c1.85 b0.66 bcd
T4M. anisopliae
AAUBC-M15		95.16 ab19.40 b1828.57 ab2.01 a0.76 ab
T5M. pinghaense
(AAUBC-M26) + 50 mM NaCl		89.60 bc16.83 c1494.97 c1.92 b0.71 abc
T6M. pinghaense
(AAUBC-M26)		96.56 a20.73 a1967.55 a2.11 a0.88 a
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Chaudhary, P.J.; B. L., R.; Patel, H.K.; Mehta, P.V.; Patel, N.B.; Sonth, B.; Dave, A.; Bagul, S.Y.; M., D.; Jain, D.; et al. Plant Growth-Promoting Potential of Entomopathogenic Fungus Metarhizium pinghaense AAUBC-M26 under Elevated Salt Stress in Tomato. Agronomy 2023, 13, 1577. https://doi.org/10.3390/agronomy13061577

AMA Style

Chaudhary PJ, B. L. R, Patel HK, Mehta PV, Patel NB, Sonth B, Dave A, Bagul SY, M. D, Jain D, et al. Plant Growth-Promoting Potential of Entomopathogenic Fungus Metarhizium pinghaense AAUBC-M26 under Elevated Salt Stress in Tomato. Agronomy. 2023; 13(6):1577. https://doi.org/10.3390/agronomy13061577

Chicago/Turabian Style

Chaudhary, Priyanka J., Raghunandan B. L., Hiren K. Patel, Punit V. Mehta, Nainesh B. Patel, Bandeppa Sonth, Anand Dave, Samadhan Y. Bagul, Divya M., Devendra Jain, and et al. 2023. "Plant Growth-Promoting Potential of Entomopathogenic Fungus Metarhizium pinghaense AAUBC-M26 under Elevated Salt Stress in Tomato" Agronomy 13, no. 6: 1577. https://doi.org/10.3390/agronomy13061577

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