According to World Agriculture, chemical fertilizer destroys soil friability, microorganisms habitat, encourage plant disease, leach away into our ground water without fully benefiting the plant and so on.
Moreover, Chemical fertilizers are primarily made from nonrenewable sources, including fossil fuels which are triggering the global warming by producing greenhouse gas (GHG). In fact, chemical fertilizers don’t replace many trace elements that are gradually depleted by repeated crop plantings, resulting in long-term damage to the soil. Repeated applications may result in a toxic buildup of chemicals such as arsenic, cadmium, and uranium in the soil. These toxic chemicals can eventually make their way into your fruits and vegetables.
National Extension Policy, Biodiversity policy, Bangladesh Bank CSR policy and even UN Sustainable Development Goals have already endorsed a development target for all nations in favor of organic fertilizer in September 2015.
As the potential area of organic fertilizer, plant endophytic bacteria will be a strong solution in the area of agriculture. This is because of bacteria from the environment, particularly plant-associated microorganisms, is useful for the development of sustainable pollution free agriculture. The phyllosphere, the vivacious plant-associated haunt, limn a microbial niche with massive agricultural and environmental importance. The plant growth and productivity closely depend on the microbial community in the phyllosphere that varies spatially.
The diversity and catabolic variations of endophytic bacteria ascribe the specific makeup of leaves, according to Rodionov et al. (2010).
Moreover, cultivars and geographical distances govern the bacterial colonization and population size of total endophytic bacteria (Madhaiyan, Poonguzhali, & Sa, 2007; Rasche et al., 2006). Similarly, the impact of geographical variation on leaf bacterial clique was illustrated by Knief, Ramette, Frances, Alonso Blanco, and Vorholt (2010). In one experiment, Firmicutes are prevalent in one area, whereas other parts show gamma proteobacteria widespread in the other parts of banana plants. Among others bacillus exhales important endophytic colonization enzymes like amylases, proteases, cellulases, and lipases, is considered as a popular endophytic bacterial genus (Kannan, Damodaran, & Uma Maheswari, 2015).
On the other hand, Proteobacteria found in oak (Uroz, Buee, Murat, Frey-Klett, & Martin, 2010) and Arabidopsis thaliana (Lundberg et al., 2012) also noted a rhizosphere (and endophyte in Arabidopsis).Besides that, several studies revealed that microbial diversity and ecosystem functions can impact plant communities in aboveground (Bonkowski & Roy, 2005). The differences in population structure in leaves are usually attributed to geographic area and leaf exudates, and also plants with different genetic backgrounds can drive different bacterial diversity on their leaf surface.
In contradiction to this, 16S rRNA gene results from leaf samples of different plant species using a culture-dependent method have demonstrated that Proteobacteria are the dominant group on leaves (Lambais, Crowley, Cury, Bull, & Rodrigues, 2006) with α – and γ-proteobacteria as major bacterial inhabitants of the phyllosphere.
In other cases, β- Proteobacteria and Firmicutes were found to be the dominant group of the bacterial community (Lambais et al., 2006). Production of siderophore is one of the traits for the bacteria to compete with other bacteria to colonize plant roots and leaves. Loaces, Ferrando, and Scavino (2011) showed that 11 rice leaf endophytic isolates were able to produce siderophore, and the isolates belonged to the genera Pantoea and Pseudomonas.
These are the representatives from the genera Pantoea, Pseudomonas, Rhodococcus, Serratia, and Klebsiella. Compared to Loaces et al. (2011), our results show a higher diversity of leaf endophytes which can produce siderophore. Siderophore-producing characters of maize endophytes were recently reported by Szilagyi-Zecchin et al. (2014). The siderophore production and antagonistic activity against plant pathogens tested had no direct correlation, suggesting a unique pattern of mechanisms involved in disease management when endophytes were explored for bioinoculant potential (Ahmad, Ahmad, & Khan, 2008).
Besides that, bacteria-producing phytohormones such as IAA, cytokinins, and gibberellin stimulate seed germination, root elongation, and plant growth. In vitro screening for characteristics commonly associated with plant growth promotion revealed that all isolates were able to produce IAA in a range of 10.24–16.71 μg/mL. IAA is one of the most studied phytohormones, which is produced in the shoot and transported to the root system.
In general, the root elongation changes based on IAA levels, and production by bacteria (particularly endophytes) may have the role in plant–microbe interaction (Ma, Prasad, Rajkumar, & Freitas, 2011).Similarly, endobacterial isolates obtained from maize (Szilagyi-Zecchin et al., 2014), tomato (Rashid, Charles, & Glick, 2012), Catharanthus roseus (Karthikeyan et al., 2012), wheat (Duran et al., 2014), and Brassica napus (Zhang et al., 2011) were able to produce IAA.
Further studies on the role of IAA in plant–bacterial interactions may reveal whether IAA is responsible for the promotion of growth, and how this IAA-producing character of bacteria helps in plant endophytic colonization.
Similarly, endophytic bacteria isolated from Alyssum serpyllifolium were found to be effective in improving Brassica juncea growth and endophytic colonization, as in the Alyssum serpyllifolium plant (Ma, Rajkumar, Luo, & Freitas, 2011). Confirmation of the plant growth-promoting bacterial effect on multiple crops is required to use the isolates as bioinoculants for many crops.
Adequate knowledge, policy, and incentives for promotion are needed to produce, market and use of organic fertilizer especially plant endophytic bacteria in Bangladesh.
Writer: M A Halim
The writer is an Assistant Professor, Department of Biotechnology, Sher-e-Bangla Agricultural University (SAU), Dhaka-1207 and a PhD fellow, Fertilizer and Soil Microbiology Lab, Department of Environmental and Biological Chemistry, Chungbuk National University (CBNU), South Korea. He can be reached at: mahalim@sau.edu.bd
BDST: 1002 HRS, JUN 27, 2017
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