7 Tropical Endophytic Bacillus Species …
163
distinct from the endophytic community. Recent studies from our research group
show that maize root-associated microbial communities have lower diversity indices
than the rhizospheric communities (Gomes et al. 2018). These results are evidenced
and consistent with previous studies showing that maize endophytic microbiota differ
from those of the rhizosphere (Edwards et al. 2015; Miliute et al. 2015; Robbins et al.
2018).
7.3 Endophytic Bacillus and Plant Growth Promotion
in Tropical Soils
Tropics occupy approximately one-third of the Earth’s surface, with different climate,
vegetation, geomorphology, lithology, and, consequently, soils in the region which
are more diverse than temperate and arctic soils (Kalpage 1974), which contributes to
the microorganism diversity. There is a growing interest in understanding the role of
endophytic microorganisms in tropical soils. The investigation of bacterial diversity
in these soils may help to describe new species and to elucidate traits related to plant
growth promotion under adverse tropical conditions.
Major factors that constrain tropical soil fertility and sustainable agriculture are
low nutrient capital, moisture stress, erosion, high P fixation, and high acidity with
aluminum toxicity (Santos et al. 2010; Camenzind et al. 2017; Garland et al. 2018).
Phosphate soluble fertilizers applied to soils can be complexed by adsorption to iron
and aluminum oxides (mainly in clayey tropical soils) and calcium precipitation
(alkaline soils), making it unavailable to plants (Novais and Smyth 1999). Phosphorus can also be complexed in organic form reaching values of up to 80% of total
P in no-till soils (Marschner et al. 2006). The fragility of many tropical soils limits
food production in annual cropping systems. Since some tropical soils under natural
conditions have high biological activity, an increased use of the biological potential of these soils to counter the challenges of food production problems is proposed
(Cardoso and Kuyper 2006). Phosphate solubilizing and mineralizing microorganism
have a high potential to be used in the management of P deficient soils. The mechanisms of P solubilization by PGPB are associated with the production of organic and
inorganic acids, proton excretion, and phosphatase activity. Organic acids decrease
the rhizosphere pH favoring the solubility of precipitated P forms. They can compete
or even replace phosphate sorbed on the surfaces of soil clays and chelate Al and Fe
avoiding thus the precipitation of phosphate (Vega 2007).
Among the common members of PGPB community, Bacillus is the most naturally
abundant and universally present endophytic genus in tropical plants (Tiwari et al.
2019). Although Bacillus is well known, there is still a range of information on
endophytes that needs to be interpreted in tropical soils so that new metabolites and
biotechnological characteristics of these bacteria can be used in medicine, industry,
and agriculture.
163
distinct from the endophytic community. Recent studies from our research group
show that maize root-associated microbial communities have lower diversity indices
than the rhizospheric communities (Gomes et al. 2018). These results are evidenced
and consistent with previous studies showing that maize endophytic microbiota differ
from those of the rhizosphere (Edwards et al. 2015; Miliute et al. 2015; Robbins et al.
2018).
7.3 Endophytic Bacillus and Plant Growth Promotion
in Tropical Soils
Tropics occupy approximately one-third of the Earth’s surface, with different climate,
vegetation, geomorphology, lithology, and, consequently, soils in the region which
are more diverse than temperate and arctic soils (Kalpage 1974), which contributes to
the microorganism diversity. There is a growing interest in understanding the role of
endophytic microorganisms in tropical soils. The investigation of bacterial diversity
in these soils may help to describe new species and to elucidate traits related to plant
growth promotion under adverse tropical conditions.
Major factors that constrain tropical soil fertility and sustainable agriculture are
low nutrient capital, moisture stress, erosion, high P fixation, and high acidity with
aluminum toxicity (Santos et al. 2010; Camenzind et al. 2017; Garland et al. 2018).
Phosphate soluble fertilizers applied to soils can be complexed by adsorption to iron
and aluminum oxides (mainly in clayey tropical soils) and calcium precipitation
(alkaline soils), making it unavailable to plants (Novais and Smyth 1999). Phosphorus can also be complexed in organic form reaching values of up to 80% of total
P in no-till soils (Marschner et al. 2006). The fragility of many tropical soils limits
food production in annual cropping systems. Since some tropical soils under natural
conditions have high biological activity, an increased use of the biological potential of these soils to counter the challenges of food production problems is proposed
(Cardoso and Kuyper 2006). Phosphate solubilizing and mineralizing microorganism
have a high potential to be used in the management of P deficient soils. The mechanisms of P solubilization by PGPB are associated with the production of organic and
inorganic acids, proton excretion, and phosphatase activity. Organic acids decrease
the rhizosphere pH favoring the solubility of precipitated P forms. They can compete
or even replace phosphate sorbed on the surfaces of soil clays and chelate Al and Fe
avoiding thus the precipitation of phosphate (Vega 2007).
Among the common members of PGPB community, Bacillus is the most naturally
abundant and universally present endophytic genus in tropical plants (Tiwari et al.
2019). Although Bacillus is well known, there is still a range of information on
endophytes that needs to be interpreted in tropical soils so that new metabolites and
biotechnological characteristics of these bacteria can be used in medicine, industry,
and agriculture.