6.15 Agriculture
Microorganisms (PGPRs) play a major role in sustaining the production and productivity of any agro-ecosystem through a myriad of roles that extend form nitrogen
fixation, nutrient solubilization, nutrient mobilization, plant growth promotion, and
the suppression of harmful pathogens and insects. Biocontrol of plant diseases using
antibiotics produced by cold-adapted bacteria, cell-wall digestive enzymes, and
toxins, or induced host resistance at low temperatures (0–5
C) are commercially
available as biocontrol agents (Bio-Green#, Plant-Helper#). They are an alternative to chemical pesticides for the control of diseases and pests in cold climates, of
winter crops, and during cold storage (Wong and McBeath 1999). Antibiotics
produced by Pseudomonas fluorescens have been commercialized for the biological
control of fire blight in pears and apples (Blightban®) (Lindow and Leveau 2002).
Arctic rhizobia increased the production of legumes by 30% through improved
nitrogen fixation and are more efficient than commercial rhizobia (Prevost et al.
2003). More recently, psychrotolerant Pseudomonas sp. PPERs23 inoculation
increased 13.4% grain yield of wheat under rainfed field condition of Indian
Himalaya (Bisht et al. 2009). In another study, coinoculation of cold tolerant
Pseudomonas spp. (PGERs17 & NARs9) with Rhizobium leguminosarum PR1
enhanced nodulation, acquisition, nutrient uptake and growth of lentil at 10
C
verifying effectiveness and specific functional compatibility relationships between
cold tolerant microbial inoculants (Mishra et al. 2010a). Application of
psychrotolerant bacterial inoculums and their agricultural importance is recently
reviewed by our groups (Mishra et al. 2010b, 2011, 2012).
Freezing injury in plants is particularly complex because of the non-uniform
behavior of different plant parts, e.g. stem, leaf, bud, flowers, etc. Also, ice nucleation in plants is frequently not endogenous, but is induced by catalytic sites present
in microbial parasites, which can be found on leaves, fruits, or stems (Lindow 1983).
A number of bacteria, such as Pseudomonas syringae and Erwinia herbicola, cause
frost injury to plants by triggering ice crystal formation through the action of INAs at
subzero temperatures. Reducing the number of such Ice
+ bacteria with naturally
occurring or genetically modified “ice-minus” mutants is claimed to be an effective
and environmentally safe method of controlling frost damage in plants. A commercial product (Frostban®) consisting of a mixture of three bacterial strains (Pseudomonas fluorescens and Pseudomonas syringae) can be sprayed on crops to protect
plants from frost (Skirvin et al. 2000; Lindow and Leveau 2002).
The development of transgenic plants with increased frost tolerance is another
exciting application. The introduction of genes from microorganisms or even whole
biosynthetic pathways in plants has already been shown to improve freeze tolerance.
Arabidopsis thaliana plants transformed with the codA gene encoding choline
oxidase and accumulating glycine betaine in the chloroplast showed a significant
improvement in freeze tolerance (Sakamota et al. 2002). Recently, Castiglioni et al.
(2008) demonstrate that bacterial Csp can confer improved stress adaptation to
multiple plant species. Transgenic rice (Oryza sativa) plants expressing CspA and
CspB manifest improved stress tolerance for a number of abiotic stresses, including
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 215
Microorganisms (PGPRs) play a major role in sustaining the production and productivity of any agro-ecosystem through a myriad of roles that extend form nitrogen
fixation, nutrient solubilization, nutrient mobilization, plant growth promotion, and
the suppression of harmful pathogens and insects. Biocontrol of plant diseases using
antibiotics produced by cold-adapted bacteria, cell-wall digestive enzymes, and
toxins, or induced host resistance at low temperatures (0–5
C) are commercially
available as biocontrol agents (Bio-Green#, Plant-Helper#). They are an alternative to chemical pesticides for the control of diseases and pests in cold climates, of
winter crops, and during cold storage (Wong and McBeath 1999). Antibiotics
produced by Pseudomonas fluorescens have been commercialized for the biological
control of fire blight in pears and apples (Blightban®) (Lindow and Leveau 2002).
Arctic rhizobia increased the production of legumes by 30% through improved
nitrogen fixation and are more efficient than commercial rhizobia (Prevost et al.
2003). More recently, psychrotolerant Pseudomonas sp. PPERs23 inoculation
increased 13.4% grain yield of wheat under rainfed field condition of Indian
Himalaya (Bisht et al. 2009). In another study, coinoculation of cold tolerant
Pseudomonas spp. (PGERs17 & NARs9) with Rhizobium leguminosarum PR1
enhanced nodulation, acquisition, nutrient uptake and growth of lentil at 10
C
verifying effectiveness and specific functional compatibility relationships between
cold tolerant microbial inoculants (Mishra et al. 2010a). Application of
psychrotolerant bacterial inoculums and their agricultural importance is recently
reviewed by our groups (Mishra et al. 2010b, 2011, 2012).
Freezing injury in plants is particularly complex because of the non-uniform
behavior of different plant parts, e.g. stem, leaf, bud, flowers, etc. Also, ice nucleation in plants is frequently not endogenous, but is induced by catalytic sites present
in microbial parasites, which can be found on leaves, fruits, or stems (Lindow 1983).
A number of bacteria, such as Pseudomonas syringae and Erwinia herbicola, cause
frost injury to plants by triggering ice crystal formation through the action of INAs at
subzero temperatures. Reducing the number of such Ice
+ bacteria with naturally
occurring or genetically modified “ice-minus” mutants is claimed to be an effective
and environmentally safe method of controlling frost damage in plants. A commercial product (Frostban®) consisting of a mixture of three bacterial strains (Pseudomonas fluorescens and Pseudomonas syringae) can be sprayed on crops to protect
plants from frost (Skirvin et al. 2000; Lindow and Leveau 2002).
The development of transgenic plants with increased frost tolerance is another
exciting application. The introduction of genes from microorganisms or even whole
biosynthetic pathways in plants has already been shown to improve freeze tolerance.
Arabidopsis thaliana plants transformed with the codA gene encoding choline
oxidase and accumulating glycine betaine in the chloroplast showed a significant
improvement in freeze tolerance (Sakamota et al. 2002). Recently, Castiglioni et al.
(2008) demonstrate that bacterial Csp can confer improved stress adaptation to
multiple plant species. Transgenic rice (Oryza sativa) plants expressing CspA and
CspB manifest improved stress tolerance for a number of abiotic stresses, including
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 215