7.1 Introduction
Agricultural augmentation in the twentieth century has been greatly attained
through the use of farm machineries, high-yielding varieties, vigorous tillage, irri-
gation, fertilizers and pesticides (Foley et al. 2005 ). This is well illustrated by the
global use of fertilizers that increased from approx. 27 to 170 million of nutrient
tonnes over the past 50 years before 2010 (Bumb and Baanante 1996 ; Heffer 2013 ).
However, continuous use of fertilizers over a long period leads to deleterious effects
on the soil. Accordingly, environmentally safe approaches have to be implemented
to maintain sustainable agricultural production to overcome threats that lead to yield
loss, including unfavourable environmental conditions to plant stress, as well as
biotic stress induced by plant pathogens and pests. Hence, it is necessary for using
endophytic bacteria for the biocontrol of plant disease and their management (Jha
et al. 2013 ).
Bacterial endophytes have been explained as bacteria isolated from internal plant
parts remain colonized in the internal tissues, not having any harmful effects to the
host (Holiday 1989 ; Schulz and Boyle 2006 ). Almost 3,00,000 plant species
existed on the earth. Among these, endophytes consist of a very few (Strobel et al.
2004 ). Of these, complete endophytic biology was studies for only few plants.
Therefore, the prospects to upbring beneficial endophyties from the diverse genera
inhabit in different ecosystems.
Bacteria may live as in soils or attached to the root surface or phyllosphere, and
may establish symbiotic relations with plants (Smith and Goodman 1999 ). Unlike
phytopathogens, endophytic bacteria do not cause any symptoms on host plants,
and their occurrence is not related to the morphological changes that appear in plant
tissues such as formation of root-nodule by symbionts. Endophytes colonize all
plant parts (inbetween the spaces of the cell walls and vascular bundles of plant
roots, stems and leaves, tissues orflowers, fruits and seeds) (Compant et al. 2011 ;
de Melo Pereira et al. 2012 ; Trognitz 2014 ). Population dynamics of endophyte
bacteria may vary from 100 to 9 109 bacteria/g of plant tissue (Misaghi and
Donnedelinger 1990 ; Chi et al. 2005 ). Generally, the highest endophytic popula-
tions is found in below ground parts when compared to above ground tissues, the
apoplastic movement of endophytic bacteria from roots to rice leaves has been
showed (Reinhold-Hurek and Hurek 2011 ). Further, roots are considered as point of
invasion of the potential endophytes from soil to the host plant.
Strong union amid host plant and endophytes is mediated through the action of
secondary metabolites produced by the microorganisms and the host cells
(Reinhold-Hurek and Hurek 2011 ; Brader et al. 2014 ). The perusal of literature
revealed the varying consequences of endophytic bacteria on plant growth.
Bacterial endophytes colonize plant tissue same as that of plant pathogens, which
can act as biocontrol agents (Berg et al. 2005 ). On the other hand, innumerable
reports exhibit the endophytic bacteria have the capability to manage several
phytopathogens (Sturz and Matheson 1996 ; Duijff 1997 ; Krishnamurthy and
Gnanamanickam 1997 ), insects (Azevedo et al. 2000 ) and nematodes (Hallmann
134 A. Muthukumar et al.