212
P. T. Lacava et al.
production of organic acids (Nautiyal et al. 2000). They can also increase P availability in the soil by secreting acid phosphatase that can mineralize organic phosphorus (van der Heijden et al. 2008). Moreover, these microorganisms can prevent
phosphate adsorption and fixation under phosphate-limiting conditions by assimilating solubilized P (Khan and Joergensen 2009). In a recent review presented by
Afzal et al. (2019), they discussed the role of plant beneficial endophytic bacteria
with special reference to phosphate solubilization as commonly found in PGPR.
For instance, around 59–100% of endophytic populations from cactus, strawberry,
sunflower, soybean, and other legumes proved to be mineral phosphate solubilizers
(Dias et al. 2009a; Forchetti et al. 2007; Kuklinsky-Sobral et al. 2004; Palaniappan
et al. 2010; Puente et al. 2009).
9.4 Endophytic Bacteria from Tropical Plants of Economic
Importance: Phosphorus Solubilization Potential
9.4.1 Endophytic Bacteria from Coffea arabica
Similar to the free living bacteria and rhizobia, the endophytes generally influence
the plant for their growth and development. These bacteria have potential to exhibit
their effects in order to benefit the plants in a befitting manner. Some of them are
given below. Coffee (Coffea arabica L.) is a perennial plant widely cultivated in many
tropical countries. It belongs to the family Rubiaceae, which has approximately 500
genera and more than 6,000 species. It is the most important genus in economic
terms, mainly due to coffee production used as beverage (Mendes et al. 1995). Due
to its continental dimensions, Brazil has a variety of climatic conditions, reliefs, altitudes, and latitudes. Such bio-geography allows for the production of many types and
qualities of coffee, including specialty coffees and organic coffee, whose consumption has increased as society has begun to question the sustainability of the current
conventional agricultural model (Brasil 2015).
The microbiota associated with coffee plants may play a critical role in coffee
quality. However, the microbial diversity and agricultural potential associated with
coffee plants are still poorly characterized. There are some examples of studies of
microorganisms associated with coffee, such as Muleta et al. (2013), who reported
phosphate-solubilizing rhizobacteria associated with Coffea arabica L. in the natural
coffee forests of southwestern Ethiopia. In this study, a total of 395 rhizobacterial isolates tested for P solubilization formed visible dissolution haloes on the
Pikovskaya’s agar (PA) culture. According to these authors, two Erwinia species
and a Pseudomonas chlororaphis produced the highest solubilization index, and
the production of organic acids by these coffee-associated strains could be considered the major mechanism involved in the solubilization of insoluble hydroxyapatite/tricalcium. Earlier, Musson (1994) suggested that endophytes can act as efficient growth promoters, probably in the same manner as rhizobacteria, by producing
P. T. Lacava et al.
production of organic acids (Nautiyal et al. 2000). They can also increase P availability in the soil by secreting acid phosphatase that can mineralize organic phosphorus (van der Heijden et al. 2008). Moreover, these microorganisms can prevent
phosphate adsorption and fixation under phosphate-limiting conditions by assimilating solubilized P (Khan and Joergensen 2009). In a recent review presented by
Afzal et al. (2019), they discussed the role of plant beneficial endophytic bacteria
with special reference to phosphate solubilization as commonly found in PGPR.
For instance, around 59–100% of endophytic populations from cactus, strawberry,
sunflower, soybean, and other legumes proved to be mineral phosphate solubilizers
(Dias et al. 2009a; Forchetti et al. 2007; Kuklinsky-Sobral et al. 2004; Palaniappan
et al. 2010; Puente et al. 2009).
9.4 Endophytic Bacteria from Tropical Plants of Economic
Importance: Phosphorus Solubilization Potential
9.4.1 Endophytic Bacteria from Coffea arabica
Similar to the free living bacteria and rhizobia, the endophytes generally influence
the plant for their growth and development. These bacteria have potential to exhibit
their effects in order to benefit the plants in a befitting manner. Some of them are
given below. Coffee (Coffea arabica L.) is a perennial plant widely cultivated in many
tropical countries. It belongs to the family Rubiaceae, which has approximately 500
genera and more than 6,000 species. It is the most important genus in economic
terms, mainly due to coffee production used as beverage (Mendes et al. 1995). Due
to its continental dimensions, Brazil has a variety of climatic conditions, reliefs, altitudes, and latitudes. Such bio-geography allows for the production of many types and
qualities of coffee, including specialty coffees and organic coffee, whose consumption has increased as society has begun to question the sustainability of the current
conventional agricultural model (Brasil 2015).
The microbiota associated with coffee plants may play a critical role in coffee
quality. However, the microbial diversity and agricultural potential associated with
coffee plants are still poorly characterized. There are some examples of studies of
microorganisms associated with coffee, such as Muleta et al. (2013), who reported
phosphate-solubilizing rhizobacteria associated with Coffea arabica L. in the natural
coffee forests of southwestern Ethiopia. In this study, a total of 395 rhizobacterial isolates tested for P solubilization formed visible dissolution haloes on the
Pikovskaya’s agar (PA) culture. According to these authors, two Erwinia species
and a Pseudomonas chlororaphis produced the highest solubilization index, and
the production of organic acids by these coffee-associated strains could be considered the major mechanism involved in the solubilization of insoluble hydroxyapatite/tricalcium. Earlier, Musson (1994) suggested that endophytes can act as efficient growth promoters, probably in the same manner as rhizobacteria, by producing