The outcome of PGPR-mediated drought tolerance may depend
on the interaction between the strain of PGPR used and soil type
(Cairns et al., 2009, 2011) as well as the plants ability to benefit
from PGPR populations occurring naturally in the soils (Den Herder
et al., 2010). Coarse sandy or gravelly soils have been reported to
allow for thinner roots to develop, which lead to improved soil
penetration, and may ultimately translate to drought tolerance
(Cairns et al., 2009). In addition, the outcome of PGPR-mediated
drought tolerance may be influenced by the duration and severity
of the stress and the age and stage of the plant’s development at
the point of drought exposure. Moreover, the performance of
effective PGPR strains must be evaluated under field conditions
where plants are more likely to experience cyclic drought rather
than continuous drought. In these evaluations the effect of PGPR on
overall crop yield should be documented. Ultimately, integrating
testing of PGPR strains into plant breeding strategies for drought
tolerance may help agriculture adapt to continued climate change.