Global Demand for Agricultural Produce Free Essay Example

Global demand for agricultural produce will increase over the coming decades, and productivity of crops must be increased particularly under tough climate conditions.(Rahi, 2017). On the other hand, it is urgent to affect the environment as little as possible.

Clearly, there is a need to move forward environmentally sustainable agriculture. One potential approach leading to reduce negative impacts of intense use of artificial fertilizers, herbicides and pesticides is the application of plant growth-promoting rhizobacteria (PGPR).

This definition was first introduced by Kloepper and Schroth (1978), to depict soil bacteria that colonize the rhizosphere, inside and above ground plant parts inciting plant growth and development through direct and indirect mechanisms (P?rez-Monta?o et al.

, 2014).

Actually, plants have had symbiotic relationships with microbes since they come to land, approximately, half a billion years (Knack et al., 2015). There have been complicated, sophisticated and continual relations between plants and a society of microbes (Smith et al., 2015). They provide necessary features for plants to develop and grow by supplying easy access to nutrients and tolerance against stressful situations.

Phyotomicrobiome

Plants have established strong connections with a great deal of microorganisms. While some microbes colonize plants just for their own benefit, others collaborate with plants in a mutually manner. Furthermore, microbes are able to indirectly impact plants by intensely changing their environments.

Unravelling the complicated interactions of plant-microbe can pave the way to increase crop yield in an environmentally friendly manner (schenk et al., 2012). Practically differnet parts of plants are colonized by microorganisms, including bacteria, archaea and fungi, collectively known as the plant-microbiome or phytomicrobiome.

The phytomicrobiome is categorized to endophytic (inside plant parts), epiphytic (on aboveground plant parts), or rhizospheric (in the soil close to the roots) according to the colonized plant parts (Kowalchuk et al., 2010, Lakshmanan et al., 2014). Microorganisms are often inseparable composition from their hostss, , and plants with their microbiome function as a metaorganism or holobiont (Bosch and McFall-Ngai, 2011, Vandenkoornhuyse et al., 2015).

Signaling in the phytomicrobiome

Rather than being an individual , plants evolving in field condition is community, but there must be a control over this community to minimize the effects of detrimental microorganism. It is increasingly evident that plants exert control over the elements of their phytomicrobiome (Smith et al., 2015).

This control occurs by the exchange of exo-hormons between plants and composition of their phytomicrobiome. Signaling also regulates activities within the phytomicrobiome, for instance through quorum sensing (Hartmann et al., 2014, Sitaraman 2015, Smith et al., 2015), and other less known signaling systems (Hagai et al., 2014). Signaling between leguminous plants and nitrogen-fixing rhizobia is one of the well characterized of signaling systems (Lira et al., 2018, Nelson and Sadowsky 2015, Smith et al., 2015, T?th and Stacey 2015 ).

Firstly, plant roots exuded isoflavonoids which absorb by rhizobia and then activate key genes within them to encode production of lipo-chitooligosaccharides (LCOs), which back to the host plant as a signal. There are various types of isoflavonoids producing by distinct legume species to control that only the proper rhizobia respond to these. Similarly, each strian of rhizobia secreted specific LCOs, in order to only the correct legume species reacts (Smith et al., 2015).

The LCOs stimulate a number of nodulation-related genes within the legume arranging nodulation process. It is said that the other phytomicrobiome composition facilitate the nodulation procedure (Maymon et al., 2015), but the related mechanisms are still unknown.

LCOs also act as signals molecules in the mycorrhizal symbiotic relationships, and for this reason this might be one of the ancient signaling systems. Nonetheless, there are distinct signal molecules in plant-to-mycorrhizal fungi symbiotic from those in plant-to-rhizobia (Smith et al., 2015). It is also interesting that rhizobia cells can produce lumichrome ,the plant growth promoting compound, another phytomicrobome signal (Dakora et al., 2002).

Bacteriocins are another group of rhizobia singals making plants compatible and competitive in their distinct habitat (Kirkup et al., 2004). In fact, bacteriocins are proteins molecules produced by bacteria which might be bacteriostatic or bacteriocidal against similar strains closed to the producers(Jack et al., 1995), so they provide producer strain with competitive benefit (Wilson et al., 1998) and if the producer strain is a proper one, it may increase occupation of nodules (Ornesik et al., 1999).

Another group of beneficial production by plant-microbe is antibiotic compounds playing a siginifcant role to control pathogens (Blomberg et al., 2007, Fravel 1988, Riley et al., 2002).

For instance, Bacteriocin thuricin 17 is isolated from soybean root tissue, and exerted by 17Bacillus thuringiensis NEB17, a non-bradyrhizobium endophytic bacterium ( Gray et al., 2006a,b). This bacteriocins are beneficial to increase growth and development in some crops (Schwinghamer et al.,2014, Subramanian,2014, Lee et al., 2009).

The phytomicrobiome and the role of PGPR

Since the time that higher plants adapted and disperesed across diverse environments, they have evolved to grow under a various conditions , and their interactions with microbes also evolved. This community, the phytomicrobiome (Smith and Zhou, 2014), with its root associated (Hirsch and Mauchline, 2012, Lundberg et al., 2012, rhizomicrobiome), above ground associated (Rastogietal,2012, 2013, Badrietal, 2013b, Kembel et al., 2014, phyllomicrobiome) and interior (Berg et al., 2014, endosphere) components.

It is becoming clear that even lower plants, for instance, Sphagnum sp. have had associations with microorganisms, including those with diazotrophs (Bragina et al., 2013). It is also reported that there have been complex interactiions among plant, soil, and microorganisms in the soil (Antoun and Prevost, 2005).

These collaborations might be detrimental, neutral or even beneficial which can meaningfully impact growth and development of plants (Adesemoye and Kloepper, 2009, Ahmad et al., 2011a, Lau and Lennon, 2011).

Diverse types of microbes, including fungi, protozoa, bacteria and actinomycetes colonise plants roots, and increment of growth by application of those microbial community is well indicated. (Bhattacharyya and Johan, 2012, Gray and Smith, 2005, Hayat et al., 2010, Saharan and Nehru, 2011, Zohar and Shad, 1996).

Bacteria are among the plentiful microorganisms populations present in the soil close to the plants roots (Kayak, 2010). Diverse genera of bacteria, Pseudomonas, Enterobacter, Bacillus, Variovorax, Klebsiella, Burkholderia, Azospirillum, Serratia and Azotobacter can significantly affect plant growth and are defined as plant growth promoting rhizobacteria (PGPR).

PGPRs play an important role in increasing plant growth and development through some direct and indirect mechanisms under both non-stress and stressful situations, (Glick et al., 2007, Nadeem et al., 2010b, Zahir et al., 2004) although the difference between mechanisms is not always distingushied (Lugtenberg and Kamilova, 2009, Ashraf et al., 2013).

Direct mechanisms include the facilitated access to nutrient by various approaches such as fixation of atmospheric nitrogen, movement of iron , mineralization and solubilization of insoluble phosphates. The production hormones stimulating plant growth and regulating stressful conditions is another type of direct mechanism. (Berg 2009, Glick et al., 2007, Hayat et al., 2010).

Indirect mechanisms involve restrictio of harmful microorganisms by breaking down the molecules secreted by pathogens, synthesis of fungal cell walls hydrolysis enzyme, enhancement of symbiotic relationships with microbes, and pest control (Das et al., 2013).

Importance of the subject

Due to climate changes, modern agriculture is exposed to a range of abiotic and biotic stresses which potentially affect crop yield (Tardieu and Tuberosa, 2010). More than half of reduction in harvest was also reported because of abiotic stresses (Bray et al., 2000).. Hence, adapting approaches intend to increase germination, growth and yield, and decrease losses prior and post harvest are becoming increasingly urgent(Gust et al., 2010).

In order to overcome the negative impacts of salinity, extreme temperature, drought stress, plants apply their adaptive and biological mechanisms, such as symbiotic relationships with microbes. Although studies on the efficacy of symbiosis under unstressed conditions are abundant , the characterization of the beneficial responses under stressful environments are few.

Canola (Brassica napus L, B. rapa L. and B. juncea L.) is a valuable crop producing one of the healthiest oil for human. . Canada is among the world’s main canola-producing countries, with 9,265 million ha, ranking third in oil production after China and Germany (USDA, 2017).  Therefore, it is inevitable to adapt new strategies to enhance yields (Lay et al., 2018).

Agronomic strategies including increasing density of seeding, changing fertilization regimes, and applying rotation crops and were successful increase canola yield (Harker et al., 2003, 2012, 2015a; Guo et al., 2005; Hwang et al., 2009), but understanding microbial associations with this economically important crop is still new, and has the potential to affect agricultural practices under stressful environments.

Thus, we aim to determine the efficacy of thuricin 17 in mitigating low temperature, drought, combination of drought and high temperature stress to improve germination and canola yield under field conditions.