160
C. C. V. Velloso et al.
rice, millet, and sorghum, with PGPB bacilli can increase productivity and food security, and reduce the use of agrochemicals and production costs contributing to a more
sustainable agriculture.
This chapter provides an overview of the importance of endophytic Bacillus from
tropical soils associated with different cereals with main emphasis on plant nutrition.
7.2 Plant Colonizing Endophytic Bacteria
Plant growth-promoting bacteria (PGPB) colonize the rhizosphere, the foliar surface
(epiphytic) or the interior of plant tissue (endophytic) providing plants with nutrients
and protection against biotic and abiotic stresses (Ahmad et al. 2008; Boddey et al.
2003; Doty et al. 2016; Franche et al. 2009; Santoyo et al. 2016; Maheshwari and
Annapurna 2017). Although, most of the research on PGPB focuses on rhizobacteria,
knowledge of endophytic bacteria has grown extensively in recent years creating a
relatively new niche and very promising approach to the development of sustainable
agriculture (Miliute et al. 2015; Santoyo et al. 2016; Xia et al. 2015).
Currently, endophytic microorganisms have been reported from nearly all host
plants studied, including crops of agronomic importance, natural and extreme conditions environments, wild and perennial plants (Nair and Padmavathy 2014; Yuan
et al. 2014; Zinniel et al. 2002). Endophytic bacteria live, at least a part of their
life cycle inside plants, apparently without causing any damage to their hosts
(Assumpção et al. 2009), which differentiates them from phytopathogenic microorganisms. Even though roots have the highest number of endophytes compared to
the shoot (Rosenblueth and Martínez-Romero 2006), endophytes have been isolated
from flowers, fruits, leaves, stems, and seeds of various plant species (Kobayashi and
Palumbo 2000; Melnick et al. 2008; Piccolo et al. 2010; Thomas et al. 2007). They
present different mechanisms of colonization, particularly roots hence considered as
a subgroup of rhizospheric bacteria that have acquired the ability to colonize plants
without inducing the host defense pathway (Marquez-Santacruz et al. 2010; Misko
and Germida 2002). Once within the plant, endophytic bacteria can exert a direct and
more effective beneficial effect compared to rhizospheric bacteria due to consistent
nutrient supply and, as they occupy the same habitat as phytopathogenic microorganisms, therefore efficient in disease control (Compant et al. 2010). In addition,
being more competitive than non-endophytic microorganisms inside the host plant
assist in the endophyte-plant interaction an evolutionary process controlled by genes
of both organisms (Rosenblueth and Martínez-Romero 2006).
According to life strategies, endophytes are classified as obligate or facultative
organisms in nature. The obligate ones are those strictly dependent on the host plant
for their growth and survival, usually transmitted by seeds and spread in the plant by
vertical colonization or by the action of a vector. Facultative endophytes have some
phases of the life cycle inside the host plant and another in which they live outside
(Hardoim et al. 2008). They constitute the majority of endophytic microorganisms
showing as characteristic of the biphasic lifestyle alternating between plant and
C. C. V. Velloso et al.
rice, millet, and sorghum, with PGPB bacilli can increase productivity and food security, and reduce the use of agrochemicals and production costs contributing to a more
sustainable agriculture.
This chapter provides an overview of the importance of endophytic Bacillus from
tropical soils associated with different cereals with main emphasis on plant nutrition.
7.2 Plant Colonizing Endophytic Bacteria
Plant growth-promoting bacteria (PGPB) colonize the rhizosphere, the foliar surface
(epiphytic) or the interior of plant tissue (endophytic) providing plants with nutrients
and protection against biotic and abiotic stresses (Ahmad et al. 2008; Boddey et al.
2003; Doty et al. 2016; Franche et al. 2009; Santoyo et al. 2016; Maheshwari and
Annapurna 2017). Although, most of the research on PGPB focuses on rhizobacteria,
knowledge of endophytic bacteria has grown extensively in recent years creating a
relatively new niche and very promising approach to the development of sustainable
agriculture (Miliute et al. 2015; Santoyo et al. 2016; Xia et al. 2015).
Currently, endophytic microorganisms have been reported from nearly all host
plants studied, including crops of agronomic importance, natural and extreme conditions environments, wild and perennial plants (Nair and Padmavathy 2014; Yuan
et al. 2014; Zinniel et al. 2002). Endophytic bacteria live, at least a part of their
life cycle inside plants, apparently without causing any damage to their hosts
(Assumpção et al. 2009), which differentiates them from phytopathogenic microorganisms. Even though roots have the highest number of endophytes compared to
the shoot (Rosenblueth and Martínez-Romero 2006), endophytes have been isolated
from flowers, fruits, leaves, stems, and seeds of various plant species (Kobayashi and
Palumbo 2000; Melnick et al. 2008; Piccolo et al. 2010; Thomas et al. 2007). They
present different mechanisms of colonization, particularly roots hence considered as
a subgroup of rhizospheric bacteria that have acquired the ability to colonize plants
without inducing the host defense pathway (Marquez-Santacruz et al. 2010; Misko
and Germida 2002). Once within the plant, endophytic bacteria can exert a direct and
more effective beneficial effect compared to rhizospheric bacteria due to consistent
nutrient supply and, as they occupy the same habitat as phytopathogenic microorganisms, therefore efficient in disease control (Compant et al. 2010). In addition,
being more competitive than non-endophytic microorganisms inside the host plant
assist in the endophyte-plant interaction an evolutionary process controlled by genes
of both organisms (Rosenblueth and Martínez-Romero 2006).
According to life strategies, endophytes are classified as obligate or facultative
organisms in nature. The obligate ones are those strictly dependent on the host plant
for their growth and survival, usually transmitted by seeds and spread in the plant by
vertical colonization or by the action of a vector. Facultative endophytes have some
phases of the life cycle inside the host plant and another in which they live outside
(Hardoim et al. 2008). They constitute the majority of endophytic microorganisms
showing as characteristic of the biphasic lifestyle alternating between plant and