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Role of Endophytes, Plant Growth Promoting Rhizobacteria

(Nadeem et al., 2013). In this particular, it was found that microbes that are

associated with plants through the symbiotic relationship help to mitigate

different stress conditions and promotes growth. Plant microbes’ association

is a very common incident and found in a plenty number of different plant

species. Plant-microbes interactions induced tolerance in plant and also help

to modulate plant response to adverse environmental conditions (Massad et

al., 2012). Different beneficial bacteria, fungi, algae, protozoa, and actinomy­

cetes that promote plants growth can be categorized into endophytes, PGPR

and arbuscular mycorrhizal fungi (AMF). Not only in the stress condition but

also in the normal condition, inoculation of plant roots with these microbes

provides better plant growth and development. These microorganisms mainly

harbor in the plant root and the rhizospheric area in the soil. The rhizosphere

is the soil area that lies near the plant root supports maximum microbial activi­

ties since root exudates provides nutrients for their growth and metabolism

(Ilangumaran & Smith, 2017).

Endophytes are symbiotic microorganisms that reside in the healthy

plants without causing any significant harm and disease. Therefore,

endophytic organisms are beneficial microbes that may be fungi, bacteria,

or viruses (Lata et al., 2018). In 1866, De Bary first time coined the term

endophytes for all the microbes that reside inside the healthy plant that do

not develop any symptoms or disease (Verma et al., 2021). Geological time

scale analysis has suggested that plant-endophytes interaction has originated

from the time of origin of the first group of higher land plants and currently

all the plants show plant-endophytes interaction. In recent time plant and

endophytes interactions gained a special position as it could induce toler­

ance in plants against environmental stressors and also helps in inhibiting

different pathogenic infections (Wiewiora et al., 2015). Endophytes can

survive various adverse environmental conditions like nutrient deficit,

drought, chilling conditions, etc. Fungal endophytes give protections to the

photosynthetic apparatus in plants from heat and high light intensity and also

induce the amount of photosynthetically active pigments (Rozpadek et al.,

2015). Some of the fungal and bacterial endophytes help in sequestration of

metals resulting in heavy metal tolerance in plants. Endophytes positively

regulate the acclimatization process in plants under adverse climatic condi­

tions and induce expression of stress responsive genes that are critical for

the plant survival. Endophytes-mediated stress tolerance includes several

direct and indirect mechanisms which includes providing enhanced nitrogen

fixing abilities, production of osmolytes, phytohormones, Reactive Oxygen

Species (ROS) scavenging enzymes, induced expression of defensive genes,