Innovations in Dryland Agriculture

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cytokinins and antioxidants by microorganisms results in abscisic acid (ABA) accu-
mulation and the degradation of reactive oxygen species. Under stress conditions,
the plant hormone ethylene endogenously regulates plant homeostasis reducing root
and shoot growth. However, ACC-deaminase-producing bacteria can reduce the
effect of stress ethylene by sequestering and degrading plant ACC (an immediate
precursor for ethylene production) to produce nitrogen and energy. Thus, the appli-
cation of ACC-deaminase-producing bacteria as bioinoculants can help to amelio-
rate the deleterious effects of stress-induced ethylene (Glick et al. 2007 ; Saleem
et al. 2007 ). Inoculation with ACC-deaminase-containing bacteria induces longer
roots which may increase the plantʼs water use efficiency due to enhanced uptake of
water from deep soil (Zahir et al. 2008 ). Many soil microorganisms produce exo-
polysaccharides which bind clay particles and organic matter to form micro- and
macro-aggregates. The application of exopolysaccharide (EPS)-producing microor-
ganisms can help to improve soil structure thus increasing water and nutrient reten-
tion in the root zone (Sandhya et al. 2009 ). The accumulation of osmoprotectants
has been correlated with abiotic stress tolerance in plants. Proline is a compatible
solute that helps plants in different ways, e.g. maintaining osmotic turgor, stabiliz-
ing macromolecules, acting as a sink for carbon and nitrogen for later use, and free
radical detoxification (Mohammadkhani and Heidari 2008 ). Similarly, Rhizobium-
mediated trehalose accumulation has been related to abiotic stress tolerance in
legumes (Figueiredo et al. 2008 ). Volatile organic compounds (VOCs) such as 2R,
3R–butanediol, salicylic acid (SA) and jasmonic acid emitted by microorganisms
are reportedly involved in IST (Grover et al. 2011 ). A further role of RNA chaper-
ones has been reported in abiotic stress tolerance. The expression of bacterial CSPs
(CSP A and CSP B) improved the tolerance of transgenic rice, maize and arabidop-
sis plants to some abiotic stresses including cold, heat and water deficit resulting in
improved yields under field conditions (Castiglioni et al. 2008 ). Inoculation with
PGPRs improved plant growth, foliar potassium concentration and leaf relative
water content under elevated CO 2 and drought (Alguacil et al. 2009 ). Under desert
farming, PGP bacteria enhanced plant photosynthetic activity and biomass synthe-
sis (up to 40 %) under drought stress (Marasco et al. 2012 ).
Thus, the selection and application of efficient microorganisms can be a useful
strategy for alleviating the negative effects of climate-change-related abiotic stresses
in plants and enhancing adaptation to climate change. Table 4 summarizes the role
of microorganisms in abiotic stress management in crop plants.


6 Conclusions

Dryland agriculture faces multiple challenges e.g., soil moisture deficit stress, high
and low temperatures, salinity, poor soil health and nutrient deficiency—which
reduce crop productivity. The changing climatic conditions are bound to exacerbate
these conditions. Further, with the expansion of dryland areas, the dependency on
these areas to contribute towards food production is increasing. Therefore, climate


M. Grover et al.
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