Background
WHY THIS PROJECT?
Urbanization and industrialization are reducing the area of arable land on the one hand, while on the other hand, we need to double food production by 2050 to feed the growing population which is set to reach nine billion (Qin et al., 2011). In order to feed the ever-increasing world population, farmers are using chemical pesticides and chemical fertilizers to boost agricultural production (Shukla et al., 2019).
These chemicals input pose a serious threat to the health of humans, animals, plants, and the entire biosphere. To minimize the chemical footprint in agricultural, plant growth promoting rhizobacteria (PGPRs) have been explored for their ability to improve plant growth and agricultural productivity (Etesami & Maheshwari, 2018).
WHY THESE OBJECTIVES?
Plant-growth-promoting rhizobacteria (PGPR) represents the group of microorganisms that colonize the root of plants and enhances plant growth either directly or indirectly (Lugtenberg & Kamilova, 2009).
PGPR improves plant growth by increasing acquisition of nutrients like phosphorus and nitrogen, and increased synthesis of phytohormones (Richardson et al., 2009; Vessey, 2003). Indirectly, PGPR improves the plant immunity against pathogenic microbes by eliciting an Induced Systemic Resistance (ISR) or Systemic Acquired Resistance (SAR), not allowing the soil-borne phytopathogens to infect plant (Bloemberg & Lugtenberg, 2001).PGPRs are widely reported to increase seed germination, plant weight, harvest yield, and disease resistance (Kloeppe et al., 1999; Kloepper et al., 1980). PGPRs are also reported to regulate photosynthesis by decreasing glucose-sensing and abscisic acid level in Arabidopsis plants (Zhang et al., 2008).Application of PGPRs also mitigates harmful effects of abiotic stresses in several crop plants (Ali et al., 2009; Hamdia et al., 2004; Kohler et al., 2009; Mayak et al., 2004).
PGPRs isolated from roots of a succulent halophyte, Salicornia brachiata improves salinity tolerance in Arachis hypogaea by reducing uptake toxic Na+ ions (Shukla et al., 2012). PGPRs regulate several physiochemical and biochemical adaptive processes to confer stress tolerance in plants (Yang et al., 2009).
Plants influence the composition of rhizomicrobiome by producing root exudates including carbohydrates, amino acids, and organic acids, are secreted in larger quantities than secondary metabolites, such as flavonoids, glucosinolates, auxins ((Backer et al., 2018; Bertin et al., 2003; Uren, 2000). Root exudates are rich source of carbohydrates, which can be more favorable to the growth of some PGPRs as compared to others (Backer et al., 2018). Carbohydrates are polyhydroxy aldehyde or ketone, and can be categorized into monosaccharide, disaccharide (oligosaccharide) and polysaccharide (Cummings & Stephen, 2007). Several reports indicated that the glucose mineralization level and the absorption of sugar by microorganisms influence the growth of PGPRs (Gunina & Kuzyakov, 2015)
In this project, I hypothesized that different carbohydrates differentially regulate the growth of different PGPRs, thus potentiate the growth promotional activity of these rhizobacteria. In this study, I would explore the effect of different saccharides as substrates to selectively enhance the beneficial bacteria in the soil, and how those bacteria effect on plant growth. I explored the effect of different carbohydrate on Ensifer fredii, Serratia proteamaculans and Pseudomonas fluorescens CHAO, and their role in plant growth promotion.
PGPR improves plant growth by increasing acquisition of nutrients like phosphorus and nitrogen, and increased synthesis of phytohormones (Richardson et al., 2009; Vessey, 2003). Indirectly, PGPR improves the plant immunity against pathogenic microbes by eliciting an Induced Systemic Resistance (ISR) or Systemic Acquired Resistance (SAR), not allowing the soil-borne phytopathogens to infect plant (Bloemberg & Lugtenberg, 2001).PGPRs are widely reported to increase seed germination, plant weight, harvest yield, and disease resistance (Kloeppe et al., 1999; Kloepper et al., 1980). PGPRs are also reported to regulate photosynthesis by decreasing glucose-sensing and abscisic acid level in Arabidopsis plants (Zhang et al., 2008).Application of PGPRs also mitigates harmful effects of abiotic stresses in several crop plants (Ali et al., 2009; Hamdia et al., 2004; Kohler et al., 2009; Mayak et al., 2004).
PGPRs isolated from roots of a succulent halophyte, Salicornia brachiata improves salinity tolerance in Arachis hypogaea by reducing uptake toxic Na+ ions (Shukla et al., 2012). PGPRs regulate several physiochemical and biochemical adaptive processes to confer stress tolerance in plants (Yang et al., 2009).
Plants influence the composition of rhizomicrobiome by producing root exudates including carbohydrates, amino acids, and organic acids, are secreted in larger quantities than secondary metabolites, such as flavonoids, glucosinolates, auxins ((Backer et al., 2018; Bertin et al., 2003; Uren, 2000). Root exudates are rich source of carbohydrates, which can be more favorable to the growth of some PGPRs as compared to others (Backer et al., 2018). Carbohydrates are polyhydroxy aldehyde or ketone, and can be categorized into monosaccharide, disaccharide (oligosaccharide) and polysaccharide (Cummings & Stephen, 2007). Several reports indicated that the glucose mineralization level and the absorption of sugar by microorganisms influence the growth of PGPRs (Gunina & Kuzyakov, 2015)
In this project, I hypothesized that different carbohydrates differentially regulate the growth of different PGPRs, thus potentiate the growth promotional activity of these rhizobacteria. In this study, I would explore the effect of different saccharides as substrates to selectively enhance the beneficial bacteria in the soil, and how those bacteria effect on plant growth. I explored the effect of different carbohydrate on Ensifer fredii, Serratia proteamaculans and Pseudomonas fluorescens CHAO, and their role in plant growth promotion.
Research Objectives
1.To increase the growth of PGPRs by supplementing with different carbohydrates
2.To enhance the plant growth promotional activity of different PGPRs in soil