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Role of Endophytes, Plant Growth Promoting Rhizobacteria

of infection. Fungal and bacterial endophytes are most unexplored diverse

groups of microorganisms that promote both plant growth and stress toler­

ance (Shiomi et al., 2006). An efficient plant-endophytes interaction needs

a successful colonization. Endophytes enter the plant in the same way as

pathogens enter the plants, but the main difference is plants develop defense

responses and secretes protective molecules against the former. Endophytic

organisms may follow some of the important stages for successful coloniza­

tion inside the plant tissue including host finding, recognition, colonization,

and entry into the internal tissue (Rodriguez et al., 2009). Fungal endophytes

are generally found in root, stem, and leave while bacterial endophytes are

mainly found in the rhizospheric area. Fungal endophytes are belonging

from two groups, clavicipitaceous endophytes (C-endophytes) and non­

clavicipitaceous endophytes (NC-endophytes). C-endophytes mainly found

in grasses and NC-endophytes grows in non-vascular plant, gymnosperms,

and angiosperms (Mei & Flinn, 2010). Both bacterial and fungal endophytes

take entry through the wound site and natural opening like stomata, lenticels,

and hydathodes. Abiotic damages and wounds caused by pathogens are the

most promising way for endophytes to take entry. In Phaseolus vulgaris, two

bacterial endophytes Enterobacter asburiae and Pseudomonas fluorescens

took entry through the damaged tissue caused by pathogen Rhizoctonia sp.

(Mahaffee & Kloepper, 1997). Endophytic microbes also secrete cell wall

degrading enzymes like cellulases, pectinases, proteinases, and hemicel­

lulases. In a study it was found that Acremonium typhinum an endophyte

secretes a proteinase during colonization in grass Poa ampla (Lindstrom &

Belanger, 1994). Temperature is another important factor in plant-endophyte

colonization. Plants with endophytes infection can tolerate 65C while non-

symbiotic association is susceptible to high temperature (Rodriguez et al.,

2008). Beside these endophytes can also transmit via seeds and other vegeta­

tive organs of plants.

Through plant-endophytes interaction both the organisms draw benefits.

Endophytes regulate different physiological processes in the plant which

promotes growth and stress tolerance. For instance, bacterial endophytes

enhance nitrogen fixation in both leguminous and non-leguminous plants

like wheat, rice, and maize (Saravanan et al., 2008). Gluconacetobacter

diazotrophicus isolated from Saccharum sp. promoted growth and nutrient

uptake under stress condition (Suman et al., 2005). Burkholderia kukruriensis

the bacterial endophytes isolated from rice plant improved root and shoot

growth and also promoted high grain yield (Mattos et al., 2008). Beside these

endophytes also regulate phytohormonal imbalance thus alter physiological