106
C. Dileep et al.
in biocontrol of plant diseases (Gardner et al. 1984). Various species mainly Pseudomonas fluorescens, Pseudomonas aeruginosa, Pseudomonas aureofaciens, Pseudomonas putida, and Pseudomonas pyrrocinia demonstrated florescent with varying
degrees of the antagonism (de Weger et al. 1986). Some of the fluorescent pseudomonads have currently received world-wide attention due to the production of
a wide range of antifungal compounds (Minaxi and Saxena 2010); siderophores;
volatile compounds such as HCN (Defago and Haas 1990), antibiotics such as
phenazine-1-carboxylic acid; pyoluteorin (Hu et al. 2005); viscosinamide and tesin
(Chin et al. 2003); 2,4-diacetylphloroglucinol (Shanahan et al. 1992); and lytic
enzymes.
The suppression of phytopathogens depends on the ability of the bacteria to colonize the roots and production of an antibiotic phenazine-1-carboxylic acid (PCA),
siderophores, and some antifungal factor (AFF). Iron-regulated, non-siderophore
antibiotics may be produced by fluorescent pseudomonads more frequently than
previously recognized, and could be partly responsible for beneficial effects that were
attributed in the past to fluorescent siderophores (Thomashow and Weller 1990). This
will lead to the nutrient imbalance in the soil. The high pH and high T.S.S (Total
Soluble Salts) creates a complex microenvironment in the rhizosphere.
The nutrient uptake by plants will be challenged in this environment and adversely
affects crop productivity (Chaudhari et al. 2013). Iron is one of the essential micronutrients and its availability to plants is limited by its non-solubility in soil. Salinity
increases the non-solubility of the iron. Iron limitation in saline soil is a multistress condition (Ferreira et al. 2019). PGPR proved effective in stress alleviation
and can be modified rhizosphere by these organisms (Backer et al. 2018). The fluorescent Pseudomonas, a reliable game-changer of iron chelation by siderophores
converts insoluble iron into available form for plant-uptake (Bakker and Schippers
1987). This chapter focuses on the mechanism of plant growth-promoting fluorescent
Pseudomonads to avoid iron limitation and assist in facilitation for the growth and
development of plants.
5.2 Interaction Between Deleterious Rhizo Bacteria (DRB)
and PGPR
Seed bacterization with fluorescent rhizosphere pseudomonads suppressed deleterious (growth-inhibiting) rhizosphere bacteria (Geels et al. 1983, 1985; Kloepper
and Schroth 1981; Schippers et al. 1985; Schroth and Hancock 1982; Suslow 1982;
Suslow and Schroth 1982). This draws support from the fact that growth promotion
is accompanied by a decrease in the number of rhizosphere microorganisms that
when reintroduced in the rhizosphere are found to adversely affect the root growth
(Suslow and Schroth 1982). The suppression of DRB and the yield decrease is the
result of at least two properties, (i) fluorescent pseudomonad isolates interfere with
the iron metabolism in the soil by converting Fe
3+ ions to a form, by complexing
C. Dileep et al.
in biocontrol of plant diseases (Gardner et al. 1984). Various species mainly Pseudomonas fluorescens, Pseudomonas aeruginosa, Pseudomonas aureofaciens, Pseudomonas putida, and Pseudomonas pyrrocinia demonstrated florescent with varying
degrees of the antagonism (de Weger et al. 1986). Some of the fluorescent pseudomonads have currently received world-wide attention due to the production of
a wide range of antifungal compounds (Minaxi and Saxena 2010); siderophores;
volatile compounds such as HCN (Defago and Haas 1990), antibiotics such as
phenazine-1-carboxylic acid; pyoluteorin (Hu et al. 2005); viscosinamide and tesin
(Chin et al. 2003); 2,4-diacetylphloroglucinol (Shanahan et al. 1992); and lytic
enzymes.
The suppression of phytopathogens depends on the ability of the bacteria to colonize the roots and production of an antibiotic phenazine-1-carboxylic acid (PCA),
siderophores, and some antifungal factor (AFF). Iron-regulated, non-siderophore
antibiotics may be produced by fluorescent pseudomonads more frequently than
previously recognized, and could be partly responsible for beneficial effects that were
attributed in the past to fluorescent siderophores (Thomashow and Weller 1990). This
will lead to the nutrient imbalance in the soil. The high pH and high T.S.S (Total
Soluble Salts) creates a complex microenvironment in the rhizosphere.
The nutrient uptake by plants will be challenged in this environment and adversely
affects crop productivity (Chaudhari et al. 2013). Iron is one of the essential micronutrients and its availability to plants is limited by its non-solubility in soil. Salinity
increases the non-solubility of the iron. Iron limitation in saline soil is a multistress condition (Ferreira et al. 2019). PGPR proved effective in stress alleviation
and can be modified rhizosphere by these organisms (Backer et al. 2018). The fluorescent Pseudomonas, a reliable game-changer of iron chelation by siderophores
converts insoluble iron into available form for plant-uptake (Bakker and Schippers
1987). This chapter focuses on the mechanism of plant growth-promoting fluorescent
Pseudomonads to avoid iron limitation and assist in facilitation for the growth and
development of plants.
5.2 Interaction Between Deleterious Rhizo Bacteria (DRB)
and PGPR
Seed bacterization with fluorescent rhizosphere pseudomonads suppressed deleterious (growth-inhibiting) rhizosphere bacteria (Geels et al. 1983, 1985; Kloepper
and Schroth 1981; Schippers et al. 1985; Schroth and Hancock 1982; Suslow 1982;
Suslow and Schroth 1982). This draws support from the fact that growth promotion
is accompanied by a decrease in the number of rhizosphere microorganisms that
when reintroduced in the rhizosphere are found to adversely affect the root growth
(Suslow and Schroth 1982). The suppression of DRB and the yield decrease is the
result of at least two properties, (i) fluorescent pseudomonad isolates interfere with
the iron metabolism in the soil by converting Fe
3+ ions to a form, by complexing