Drought is one of the major constraints limiting agricultural production worldwide and is
expected to increase in the future. Limited water availability causes significant effects to
plant growth and physiology. Plants have evolved different traits to mitigate the stress
imposed by drought. The presence of plant growth-promoting rhizobacteria (PGPR) could
play an important role in improving plant performances and productivity under drought.
These beneficial microorganisms colonize the rhizosphere of plants and increase drought
tolerance by lowering ethylene formation. In the present study, we demonstrate the potential
to improve the growth of velvet bean under water deficit conditions of two different strains of
PGPR with ACCd (1-Aminocyclopropane-1-Carboxylate deaminase) activity isolated from
rainfed farming system. We compared uninoculated and inoculated plants with PGPR to
assess: a) photosynthetic performance and biomass; b) ACC content and ethylene emission
from leaves and roots; c) leaf isoprene emission. Our results provided evidence that
under drought conditions inoculation with PGPR containing the ACCd enzyme could
improve plant growth compared to untreated plants. Ethylene emission from roots and
leaves of inoculated velvet bean plants was significantly lower than uninoculated plants.
Moreover, isoprene emission increased with drought stress progression and was higher in
inoculated plants compared to uninoculated counterparts. These findings clearly illustrate
that selected PGPR strains isolated from rainfed areas could be highly effective in promoting
plant growth under drought conditions by decreasing ACC and ethylene levels in plants.