Читать книгу Phytomicrobiome Interactions and Sustainable Agriculture - Группа авторов - Страница 22

Plants are meta‐organisms which are the multicellular organisms encompassing a synergistic association with a suite of microorganisms such as fungi, bacteria, archaea, and viruses, as well as several algal symbionts (Bosch and McFall‐Ngai 2011). Practically every plant component is colonized by a consortium of microorganisms, which in combination is designated as “plant microbiome” or“phytomicrobiome.” Based on their habitation, the microbes are categories as endophytic (within the plant tissue), epiphytic (on the surface of the above‐ground part), and rhizospheric (within or on the root surface) (McFall‐Ngai 2002, 2008). The microbiome composition and their metabolic activity determines the interaction and sustenance of the host plant within the surrounding environment (Kostic et al. 2013). The rhizospheric zone of the plant hosts a high density of microbial population enthralled with high microbial activity as compared with the other zones of plant habitation even within the surrounding bulk soil (Santoyo et al. 2016). Nonetheless, the microbial diversity is low as compared to the bulk soil and the composition within the bulk soil and rhizosphere are pretty distinct indicating stringency in the selection of microbial population (Pisa et al. 2011).

Years of research have contributed to identifying the associations of microbes with subtly distinguished parts of the plants such as epiphytic and endophytic regions of both stems and leaves of the phyllospheric region; the rhizosphere and the reproductive components such as seeds, fruits, flowers, etc. In the epidermal region of the grape plant along with the xylem of ovaries and ovules, two species of bacillus and the Pseudomonas species have specifically been found to colonize endophytically, whereas only the Bacillus species have been found to colonize the seed cell wall of berries (Lugtenberg and and Kamilova 2009; Compant et al. 2010a, 2010b). The plant growth–promoting rhizobacteria such as Diazotrophicus, Acetobacter, etc., (Quecine et al. 2012) assist the plant to fix nitrogen from the atmosphere and have an affinity to the plant roots (Pisa et al. 2011) and stem regions of the sugarcane plant and have been found to reside in the apoplastic zone under a low‐nitrogen and high‐sucrose situation.

The major hub of the interspecies associations that happen is at the rhizosphere which surrounds the roots area of the plants. The population of colonization depends upon the biochemistry of the plant and the microbes plus the available resources within the soil of that locality. One such species that is present in the majority of rhizosphere is the Streptomyces sp. They deserve a special mention because they can colonize not only the parts of the plants associated with the soil but also the parts above the ground. These microbes offer a variety of benefits to the host plant where they release antibiotic substances, thereby rendering the plant protected from the malicious conditions present in the surroundings. They are particularly useful as biocontrol agents where they protect various crop plants against pathogenic as well as environmental stresses. They serve as biofertilizers as well owing to their plant growth–promoting abilities. Their sporulating ability aids their survival in the adverse environment rendering them competent over the other microbes. This species releases various lytic enzymes that can metabolize insoluble organic substances to generate nutrients which are imperative for the proper growth and functioning of plants.

The aspect of microbial plant growth promotion can also be utilized for phytoremediation when dealing with a plant sown in a soil laden with high metal contamination. Bioethanol producers such as Helianthus tuberosus, a high biomass yielding crop acquires enhancement in the accumulation and sustenance of high concentrations of zinc and cadmium. In another case, the microbial population has been found to be colonizing the internal region of the roots as an endophyte; thereby resulting in increased assimilation of cadmium. The key feature of the presence of metal‐solubilizing bacteria is that it makes the host plant tolerant and decreases the effect of metal‐induced stress (Montalbán et al. 2017).

Interestingly, such a phenomenon has also been observed for the enhanced salt and drought resistance owing to the effects of plant growth–promoting bacteria as studied in Lolium perenne, also known as ryegrass. Unfortunately for this perennially relevant grass, as turf and forage, it is highly sensitive to drought‐induced stress and high salinity. However, Bacillus amyloliquefaciencs combined with hydrogels to prevent the soil from eroding can help the grass sustain the drought‐induced stress by the plant (Su et al. 2017).

In the cotton plant, arbuscular mycorrhizal fungus is a soil‐borne mutualistic symbiotic association with the terrestrial planets. One strain, Rhizophagusirregularis, acts antagonistically to the growth of Verticillium dahlia colonization and induces resistance by releasing the unknown volatiles thereby saving a most important crop plant (Zhang et al. 2018).

A beautiful symphony gets established to carry out mundane functions. The microbiome communities specific to the phyllosphere affect the development of plants along with its function within the ecosystem, whereas the host plant modulates the composition and effector functions of the phytomicrobiome. Environmentally governed factors have been found to amend several metabolite biosynthesis within the plant. Since the roots play a major role in establishing the health of the plant, the rhizomicrobial species participate in modulating plant growth, composition, and development. Interestingly enough, a study was found where just by treating the leaves with a specific consortium of phyllomicrobiome led to the prevention of feeding on the leaves by insect larvae (Badri et al. 2013).

However, it is believed that microbial community composition and their distribution in the phyllospheric region are somewhat arbitrary. Nonetheless, there is high‐level specificity in accommodation of the microbial communities within the endospheric and rhizospheric regions (Lebeis 2015).

The study for an in‐depth understanding of means of interaction has been attempted through studies involving biochemical, metabolomics, proteomics, and genomics studies. These studies aid in assimilating the knowledge pertaining to the direction of devising methods to enhance the yield of crop produce and biomass production without many additional inputs (Lebeis 2015). Knowledge of this kind underpins the engineering requirements of the phytomicrobiome, thereby catering in the manipulation of the beneficial consortium composition. This, in turn, caters to the plant microbial associations which bear the responsibility of generating signals that enhances the ability of the phytomicrobiome community to overcome various climatic and soil‐related stressed or undesirable conditions leading to overall crop productivity (Quecine et al. 2012).