Abstract

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.

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