Co-inoculation of soybean with Bradyrhizobium and PGPB resulted in an increase in
nodule number and shoot dry weight (Zeffa et al. 2020). Co-inoculation of a Bacillus
strain with Rhizobium leguminosarum enhanced plant growth and nodulation of pea
and lentil (Mishra et al. 2009; Schwartz et al. 2013). A Bacillus strain increased
nodulation of Phaseolus vulgaris in combination with Rhizobium tropici CIAT
899 and this beneficial effect occurred under controlled as well as under field
conditions (Camacho et al. 2001). Co-inoculation of chickpea with nitrogen-fixing
and phosphorus-solubilizing bacteria improved nodulation, plant growth, and yield
(Elkoca et al. 2007), and co-inoculation of PGPR and rhizobia was shown to have a
synergistic effect on bean growth (Korir et al. 2017).
21.1.1 What About Potential Pathogens That May Affect
Animals or Humans?
The most prevalent microbes in the soil are likely to be those associated with plants
because plants are sources of carbon, which is needed for heterotrophic bacteria and
fungi. However, depending on the land’s use, soil can also be “home” to animal and
human pathogens. Land that is used for crop production and pasture for various
animals often houses potential pathogens such as Bacillus anthracis, E. coli,
Enterobacter cloacae, Pseudomonas aeruginosa, and many others. However, at
the same time, many of these isolates positively affect plant growth. Strategies for
determining the potential pathogenicity of microbial isolates can be found in the
following reference (Martínez-Hidalgo et al. 2018) and the references therein.
21.2 Symbiosis as an Evolutionary Driving Force
All plant roots have microbiomes, but the larger question is: how did this interaction
become established between soil microbes and plant roots at the very beginning of
land plant evolution? For an answer, we need to go into the earliest records of the
evolution of plants, their roots, and in some cases, their associated microbes, which
were all present at least 420 to ca. 360 million years ago (Mya), in the Devonian.
Early on, the land masses were clustered together and surrounded by shallow seas.
They were not arranged at that time on Earth the way we are accustomed to seeing
them now from satellite photos and maps. It was the Age of the Fishes and the
beginnings of vascular plant root evolution on land. Evidence of bacterial presence
in oceans dates back at least 3.5 billion years ago (Gya), but data remain controversial with respect to land colonization. Support had also come from isotopic signatures dating from 2.6 to 2.7 Gya based on Watanabe et al. (2000). These authors
reported that land colonization was likely based on the presence of soil-surface
microbial mats, consisting of sheathed cyanobacteria and thin filaments (i.e., lichen430
S. Kouas et al.
nodule number and shoot dry weight (Zeffa et al. 2020). Co-inoculation of a Bacillus
strain with Rhizobium leguminosarum enhanced plant growth and nodulation of pea
and lentil (Mishra et al. 2009; Schwartz et al. 2013). A Bacillus strain increased
nodulation of Phaseolus vulgaris in combination with Rhizobium tropici CIAT
899 and this beneficial effect occurred under controlled as well as under field
conditions (Camacho et al. 2001). Co-inoculation of chickpea with nitrogen-fixing
and phosphorus-solubilizing bacteria improved nodulation, plant growth, and yield
(Elkoca et al. 2007), and co-inoculation of PGPR and rhizobia was shown to have a
synergistic effect on bean growth (Korir et al. 2017).
21.1.1 What About Potential Pathogens That May Affect
Animals or Humans?
The most prevalent microbes in the soil are likely to be those associated with plants
because plants are sources of carbon, which is needed for heterotrophic bacteria and
fungi. However, depending on the land’s use, soil can also be “home” to animal and
human pathogens. Land that is used for crop production and pasture for various
animals often houses potential pathogens such as Bacillus anthracis, E. coli,
Enterobacter cloacae, Pseudomonas aeruginosa, and many others. However, at
the same time, many of these isolates positively affect plant growth. Strategies for
determining the potential pathogenicity of microbial isolates can be found in the
following reference (Martínez-Hidalgo et al. 2018) and the references therein.
21.2 Symbiosis as an Evolutionary Driving Force
All plant roots have microbiomes, but the larger question is: how did this interaction
become established between soil microbes and plant roots at the very beginning of
land plant evolution? For an answer, we need to go into the earliest records of the
evolution of plants, their roots, and in some cases, their associated microbes, which
were all present at least 420 to ca. 360 million years ago (Mya), in the Devonian.
Early on, the land masses were clustered together and surrounded by shallow seas.
They were not arranged at that time on Earth the way we are accustomed to seeing
them now from satellite photos and maps. It was the Age of the Fishes and the
beginnings of vascular plant root evolution on land. Evidence of bacterial presence
in oceans dates back at least 3.5 billion years ago (Gya), but data remain controversial with respect to land colonization. Support had also come from isotopic signatures dating from 2.6 to 2.7 Gya based on Watanabe et al. (2000). These authors
reported that land colonization was likely based on the presence of soil-surface
microbial mats, consisting of sheathed cyanobacteria and thin filaments (i.e., lichen430
S. Kouas et al.