Unleashing Bacillus species as versatile antagonists: Harnessing the biocontrol potentials of the plant growth-promoting rhizobacteria to combat Macrophomina phaseolina infection in Gloriosa superba

Charcoal rot caused by Macrophomina phaseolina is one of the most devastating diseases that cause severe yield loss in Gloriosa superba cultivation. Plant growth-promoting rhizobacteria (PGPR) are extensively harnessed as biocontrol agents due to their effectiveness in combating a wide array of plant pathogens through a multifaceted approach. The present study delved into the mechanisms underlying its ability to inhibit root rot pathogen and its capacity to promote plant growth in G. superba, commonly known as glory lily. PGPR isolated from the rhizosphere of glory lily were subjected to in vitro assessments using the dual plate technique. The isolated Bacillus subtilis BGS-10 and B. velezensis BGS-21 showed higher mycelial inhibition (61%) against M. phaseolina. These strains also promote plant growth by producing indole-3-acetic acid, siderophore, ammonia, amylase, cellulase, pectinase, xylanase, and lipase chemicals. Genome screening of BGS-10 and BGS-21 revealed the presence of antimicrobial peptide genes such as Iturin (ituD gene), surfactin (srfA and sfp genes) along with the mycolytic enzyme β-1,3-glucanase. Further, the presence of secondary metabolites in the bacterial secretome was identified through gas chromatography-mass spectrometry (GC/MS) analysis. Notably, pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl), 9 H-pyrido[3,4-b] indole and L-leucyl-D-leucine exhibited the highest docking score against enzymes responsible for pathogen growth and plant cell wall degradation. Under glasshouse conditions, tuber treatment and soil application of talc-based formulation of B. subtilis BGS-10 and B. velezensis BGS-21 suppress the root rot incidence with a minimal disease incidence of 27.78% over untreated control. Concurrently, there was a notable induction of defense-related enzymes, including peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL), in glory lily. Therefore, it can be concluded that plant growth-promoting Bacillus strains play a significant role in fortifying the plant's defense mechanisms against the root rot pathogen.

Genetic diversity, symbiotic efficiency, stress tolerance, and plant growth promotion traits of rhizobia nodulating Vachellia tortilis subsp. raddiana growing in dryland soils in southern Morocco

In the present study, we analyzed the genetic diversity, phylogenetic relationships, stress tolerance, phytobeneficial traits, and symbiotic characteristics of rhizobial strains isolated from root nodules of Vachellia tortilis subsp. raddiana grown in soils collected in the extreme Southwest of the Anti-Atlas Mountains in Morocco. Subsequent to Rep-PCR fingerprinting, 16S rDNA gene sequencing of 15 representative strains showed that all of them belong to the genus Ensifer. Phylogenetic analysis and concatenation of the housekeeping genes gyrB, rpoB, recA, and dnaK revealed that the entire collection (except strain LMR678) shared 99.08 % to 99.92% similarity with Ensifer sp. USDA 257 and 96.92% to 98.79% with Sinorhizobium BJ1. Phylogenetic analysis of nodC and nodA sequences showed that all strains but one (LMR678) formed a phylogenetic group with the type strain "E. aridi" LMR001^T (similarity over 98%). Moreover, it was relevant that most strains belong to the symbiovar vachelliae. In vitro tests revealed that five strains produced IAA, four solubilized inorganic phosphate, and one produced siderophores. All strains showed tolerance to NaCl concentrations ranging from 2 to 12% and grew at up to 10% of PEG6000. A greenhouse plant inoculation test conducted during five months demonstrated that most rhizobial strains were infective and efficient. Strains LMR688, LMR692, and LMR687 exhibited high relative symbiotic efficiency values (respectively 231.6 %, 171.96 %, and 140.84 %). These strains could be considered as the most suitable candidates for inoculation of V. t. subsp. raddiana, to be used as a pioneer plant for restoring arid soils threatened with desertification.

Biochemical traits of Bacillus subtilis MF497446: Its implications on the development of cowpea under cadmium stress and ensuring food safety

The present study aimed at assessment of different application methods of Bacillus subtilis MF497446 to induce development of cowpea ensuring food safety under cadmium (Cd) stress. Also, isolation, plant growth promoting (PGP) traits and 16 S rRNA-based identification of Bacillus subtilis MF497446 is documented. Out of 24 Bacillus isolates (AS1-AS24), only four isolates (AS4, AS12, AS14 and AS22) showed greater Cd tolerance up to 18 mg L^-1. The greatest PGP traits under Cd stress were displayed by Bacillus isolate (AS12); which, also, enhanced seedling elongation and vigor index of cowpea under Cd stress. Phylogenetic analysis, based on 16 S rRNA, confirmed that this promising Bacillus isolate (AS12) belongs to Bacillus subtilis and is referred to as B. subtilis MF497446. Treatment of inoculation+soaking for 90 min of cowpea seeds by B. subtilis MF497446 resulted in the best development of cowpea plants under Cd stress (up to 9 mg kg^-1); as fresh and dry masses of cowpea increased from 6.80 to 1.54 to 12.35 and 2.59 g plant^-1, respectively. Moreover, shoot and root lengths were 19.66 and 28.33 cm when cowpea seeds were treated by B. subtilis MF497446 (inoculation+soaking for 90 min) compared to 11.33 and 10.66 cm, respectively, for control (Cd stress only). Application of B. subtilis MF497446 (as inoculation+soaking for 90 min) reduced Cd accumulation and bioconcentration factor in cowpea plants by 29.2 and 28.9%, respectively, compared to control (Cd stress only). These results clearly reveal that applying of B. subtilis MF497446 to crops grown on Cd-contaminated soil enhances plant growth and eliminates (or at least diminishes) the risks to human health ensuring food safety.

Complete genome sequence of plant growth promoting Pseudomonas aeruginosa AJ D 2 an isolate from monocropic cotton rhizosphere

A plant growth promoting Pseudomonas aeruginosa AJD 2 was isolated from monocropic cotton rhizosphere of Maharashtra state, India. The strain was identified as per physiological, biochemical and 16S rRNA gene sequencing (Accession number MG234531). The strain possess multiple functional plant growth promoting traits and antifungal activity. The genome was extracted, purified and library of avg.515 bp was prepared and sequenced by over Illumina platform. The sequenced genome was studied by using CLC workbench and NCBI pipeline using Pseudomonas aeruginosa PAO1 and Pseudomonas aeruginosa YL84 as reference assembler. The size of the genome is 6.1 Mb with 5802 genes within it. The study over strain may give an insight into its plant growth promotion mechanism.

Evaluation of the production of exopolysaccharide by plant growth promoting yeast Rhodotorula sp. strain CAH2 under abiotic stress conditions

The capability of plant growth promoting microbes to survive under abiotic stresses has important significance for improving plant growth and productivity. Among the various plant growth promoting biomolecules produced by microbes, exopolysaccharide (EPS) help microbes to survive in inhospitable environments and endure environmental stressful conditions. In the present study, a yeast strain CAH2 was isolated from Beta vulgaris rhizosphere soil and identified as Rhodotorula sp., based on the partial 18S rRNA gene sequence analysis. Rhodotorula sp. strain CAH2 was found to tolerate higher concentrations of Al (6 mM), NaCl (150 mM) and PEG-6000 (15%, w/v). The strain CAH2 was shown to produce 7.5 g L^-1 of EPS in the production medium with sucrose and yeast extract as a carbon and nitrogen sources, respectively. The EPS yield was increased constantly with increasing concentrations of Al, NaCl and PEG-6000. The structural feature of EPS studied through FT-IR and NMR spectral analysis confirmed the presence of glucose, mannose and galactose. The yeast strain CAH2 was produced multiple plant growth promoting traits in the presence and absence of abiotic stresses. Finally, these results indicate that the production of EPS could be safeguard the plant growth promoting Rhodotorula sp. strain CAH2 from unfavourable environmental conditions.