FIGURE 3.1 Different environmental stress and the mechanisms through which rhizosphere

microorganisms induced stress tolerance in plants.

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Role of Endophytes, Plant Growth Promoting Rhizobacteria

3.2 PLANT AND DIFFERENT ENVIRONMENTAL STRESSES

Plants may be subjected to different environmental stresses through different

abiotic and biotic factors. Stress can be defined as any adverse environmental

condition which limits plants growth and development. In plant stress is

caused by the principal abiotic factors like heat, salinity, cold, water logging,

drought, heavy metals, nutrients deficit, intense light and also by biotic factors

including pathogens and different pests (Lichtenthaler, 1998; Wahid et al.,

2007). Abiotic stressors are the main challenge in the agricultural sector as it

is responsible for the main yield losses every year worldwide. The scarcity

of available water in the soil is responsible for different stress conditions like

drought and salinity. Application of fertilizer along with irrigation and low

rainfall greatly influenced salinity stress. It was reported that about 64% of

the total arable land area of the world is under drought condition and 6% area

is under salinity stress (Cramer et al., 2011). Drought is the most destructive

stress condition that exhibit effects both at morphological and cellular level.

One of the main effects of drought stress is reduced germination of seedlings

(Nezhadahmadi et al., 2013). In addition to this, drought stress also inhibits

photosynthetic efficiency of plants by decreasing leaf expansion along