Sugarcane Peking 1985 |BEST|
Biological control agents (BCAs) provide cost-effective, environmentally friendly pest and pathogen control in many crops, including sugarcane (Li et al., 2018; Jayakumar et al., 2019). The method of achieving biological control is complex and cannot be effective in certain production conditions. A range of non-pathogenic microbial species has the potential to trigger induced systemic resistance (ISR) by producing elicitors that trigger immune responses in plants (Cawoy et al., 2014). Plant growth-promoting endophytic bacteria (PGPEB) are microorganisms that reside and colonize inside plant tissue have also been explored widely for host plant resistance to pathogen attacks (Choudhary et al., 2007; Kumar et al., 2017). These bacteria simply enter the plant roots through various means and promote plant growth through different mechanisms, such as plant growth regulators, phosphate solubilization, nitrogen-fixation, ethylene metabolism, and indirect disease resistance mechanisms by antimicrobial metabolites or siderophores that suppress pathogenic microbes (Sun et al., 2009; Olanrewaju et al., 2017). Hence, the use of PGPEB is receiving a renewed interest as a green alternative to agrochemicals for sustainable agriculture.
Sugarcane Peking 1985
In plant-associated environments, Pseudomonas organisms are ubiquitous and play a significant role in the natural defense of plants against pathogens (Mendes et al., 2007). Bacteria belonging to the genus Pseudomonas protect plants by direct competition with or being antagonistic to pathogens (Haas and Défago, 2005; Bakker et al., 2007). Many Pseudomonas species, especially P. fluorescens, P. putida, P. chlororaphis, and P. syringe, are well recognized for their ability to stimulate plant growth and control a range of plant pathogens (Raaijmakers and Mazzola, 2012; Li et al., 2017). Some of the earlier literature reported the isolation of Pseudomonas strains from sugarcane: Pseudomonas spp., P. aeruginosa, P. aurantiaca, P. fluorescens, P. putida, P. reactans, P. monteilii, P. plecoglossicida, P. entomophila, P. koreensis, and P. mosselii (Viswanathana and Samiyappan, 2002; Viswanathan et al., 2003; Mendes et al., 2007; Mehnaz et al., 2009, 2010; Magnani et al., 2010; Li et al., 2017). P. aeruginosa strains are touted to be an important tool for disease management programs in tropical countries owing to their biocontrol effectiveness against several pathogens (Kumar et al., 2013). However, P. aeruginosa is often referred to as an opportunistic pathogen that colonizes various groups of organisms, and a comprehensive understanding of P. aeruginosa strains is limited.
Antifungal activity of strain B18 against Sporisorium scitamineum, Ceratocystis paradoxa, and Fusarium verticillioides sugarcane pathogens. The first row shows control plates, the second row shows growth inhibition of pathogens by strain B18 in dual culture plate assay, and the third row shows the agar well diffusion method. C (control).
CLSM and SEM micrographs images showing morphology and colonization of Pseudomonas aeruginosa B18 in sugarcane variety (Yacheng71-374). (A,B) is rod-shaped morphology of B18 strain, (C,D) is the colonization of B18 in stem tissue of sugarcane, and (E,F) is the colonization of B18 on the root surface of sugarcane. CLSM images confirming inoculated GFP tagged B18 strain as green dots in sugarcane tissues.
qRT-PCR expression analysis of pathogen defense-related genes in the leaf of smut susceptible sugarcane variety (Yacheng71-374) four weeks following treatments. The data were standardized to the level of the GAPDH expression. The mean SE is viewed as all data points (n = 3) and the same letters show no difference between treatments at p-value
Endophytic bacterial strains support plant growth via diverse direct and indirect systems, such as producing IAA, cytokinin, and GA3 phytohormones (Hardoim et al., 2015), P- solubilization, siderophores secretion, and plant resistance to biotic and abiotic stresses (Rosenblueth and Martínez-Romero, 2006; Gaiero et al., 2013; Lebeis, 2014). In this study, strain B18 showed IAA production, and comprehensive genome analysis established the presence of trpABCDEG genes related to IAA production. The occurrence of tryptophan-linked genes in the genome of bacteria is well-established, and it is associated with IAA biosynthesis (Tadra-Sfeir et al., 2011; Gupta et al., 2014). Similar to our results, complete genome analysis of Sphingomonas sp. LK11 and Enterobacter roggenkampii ED5 showed the existence of trpABD and trpBE genes, responsible for IAA production (Asaf et al., 2018; Guo et al., 2020). Previously, P. aeruginosa strain NJ-15 has been reported to produced IAA and biocontrol activity (Bano and Musarrat, 2003). In another study, P. aeruginosa BG was shown to produce IAA and promote growth enhancement in Chickpea (Goswami et al., 2013). Consistent with these findings, in this study, we observed improved growth of sugarcane plant after B18.
Biotic stress also affects plant yield by increasing the level of intracellular ROS, causing tissue damage, and the production and exclusion of ROS in plants are retained by the activity of several antioxidant enzymes (Gupta and Datta, 2003). Bacteria produce cell-wall-degrading enzymes and different metabolites that prevent the growth of pathogenic microbes (Shoda, 2000; Chernin and Chet, 2002). Certain bacteria activate a phenomenon identified as ISR to refer to stress-related physical and chemical adaptations in plants against pathogens attack. The metabolic pathways in plants are either up-or downregulated under stress at diverse developmental stages, altering plant growth (Chaves et al., 2002). The majority of information on ISR is associated with rhizobacterial strain, but some endophytic bacteria have also been reported to include ISR activity. For instance, P. fluorescens EP1 activated ISR in response to Colletotrichum falcatum pathogen causing sugarcane red rot disease (Viswanathan and Samiyappan, 1999).
Figure 4. Scanning electron microscopy (SEM) and CLSM micrographs of most efficient endophytic E. roggenkampii ED5 strain and its colonization in sugarcane plant parts at the root and stem regions. Panels (A,B) is the SEM images showing the morphology of ED5 strain and, (C,D) is the colonization images obtained after the inoculation of ED5 strain in root and stem tissues of sugarcane. Panels (E,F) showing the CLSM micrographs of GFP-tagged endophytic ED5 strain, and (G,H), showing the colonization in the roots and stems of sugarcane by GFP-tagged E. roggenkampii ED5. CLSM images showing the selected strain ED5 in green dots of auto-fluorescence in both root and stem tissues, respectively, and bacterial cells are specified by blue and white arrowheads. Both micrographs confirmed the colonization of inoculated endophytic E. roggenkampii ED5 strain in sugarcane.
Environmentally protected approaches such as bio-fertilizers are seriously required to improve crop/sugarcane growth, nitrogen fixation, and reduce yield loss in different stress conditions to retain sustainable crop production. The utilization of plant growth-promoting (PGP) endophytic bacteria is an efficient approach to stabilizing and improving crop yield due to these bacteria may have ecological benefits more than epiphytic and rhizospheric bacteria as they directly contact with the plants (James, 2000). Endophytic microbes, inhabit and survive inside plant tissue are widely investigated in several plants (Hardoim et al., 2015; Kumar et al., 2017), can support plant growth by several ways such as improving the soil nutrient uptake and germination rate, altering the phytohormone levels and improving plant biotic and abiotic stresses. In addition, secondary aids consist of the biological control of plant pathogens and the induction of induced systemic resistance (ISR) in plants (Rosenblueth and Martínez-Romero, 2006; Ryan et al., 2008; Mei and Flinn, 2010).
The complete-genome study can be used to categorize genes implicated in the positive effects of plant growth-promoting bacteria (PGPB), offer the perception of the molecular and functional mechanisms (Kang et al., 2016; Qin et al., 2017; Oh et al., 2018). Earlier, complete genome analysis of some other Enterobacter stains is accessible (Ren et al., 2010; Taghavi et al., 2010; Liu et al., 2012; Andrés-Barrao et al., 2017) excluding E. roggenkampii. Therefore, the complete genome sequence accessibility of endophytic E. roggenkampii isolated from sugarcane root will help in full understanding of the diverse biological mechanisms and determining the characteristics of this bacteria, plus gene identification that is contributing to the positive activity of PGPB, improve sugarcane growth under abiotic and biotic stresses.
Scanning electron microscopy (SEM) and CLSM micrographs of most efficient endophytic E. roggenkampii ED5 strain and its colonization in sugarcane plant parts at the root and stem regions. Panels (A,B) is the SEM images showing the morphology of ED5 strain and, (C,D) is the colonization images obtained after the inoculation of ED5 strain in root and stem tissues of sugarcane. Panels (E,F) showing the CLSM micrographs of GFP-tagged endophytic ED5 strain, and (G,H), showing the colonization in the roots and stems of sugarcane by GFP-tagged E. roggenkampii ED5. CLSM images showing the selected strain ED5 in green dots of auto-fluorescence in both root and stem tissues, respectively, and bacterial cells are specified by blue and white arrowheads. Both micrographs confirmed the colonization of inoculated endophytic E. roggenkampii ED5 strain in sugarcane.
Also, genes involved in plant resistance response, i.e., antimicrobial peptide, synthesis of resistance inducers, hydrolase genes such as chitinase, cellulase, α- amylase, GTP cyclohydrolase, glutamate dehydrogenase, xylan 1,4beta-xylosidase, and glucosidase, whereas, oxidoreductases genes such as superoxide dismutase (SOD), glutathione peroxidase (GPX) and peroxiredoxin (PRXS) were also categorized (Table 5). Strain ED5 genome predicted some key genes of volatile substances such as 2,3-butanediol (alsD and ilvABCDEHMY), methanethiol (metH and idi) and isoprene (gcpE and ispE) and might be involved in biocontrol mechanism of strain ED5 (Table 5). Some symbiosis-related genes were also observed in strain ED5 genome, which might play a role in the establishment of symbiosis with the sugarcane plant (Table 5). 041b061a72