Pseudomonas chlororaphis as a potential Plant Growth Promoting Rhizobacteria for enhancing barley performance under drought stress

Drought is one of the major abiotic stresses affecting crops. Traditional breeding and genetic approach are applied to mitigate the effects of the drought. However, crop tolerance to abiotic stresses involves quantitative traits and many genes, therefore the plant adaptation to stresses should be improved by various sustainable strategies (Ali et al., 2022). Sustainability in agriculture without affecting the yield of the crops is one of the main areas of research in recent years. Plant growth promoting rhizobacteria (PGPR) could very well achieve this goal as they are excellent plant biostimulants. Due to their diverse nature and activity on the plants, PGPR can play an important role in improving the growth of plants, the yield, and crop tolerance to abiotic stress events, such as long period of drought (Ferioun et al., 2023), whose frequency is increasing due to climate change. The aim of the present study was to evaluate the interaction between Pseudomonas chlororaphis subspecies aureofaciens inoculation and six genotypes of barley in controlled condition under drought stress. The selected genotypes of barley involved facultative (Lunet and Pamina), spring (Tremois and Morex), and winter (Nure and Ponente) growing habit. A randomized complete design was used with six genotypes, two treatments (inoculated and non-inoculated) and two irrigation regimes (soil moisture at 20% as stress and soil moisture at 40% as control). Twelve biological replicates were considered. Seeds of barley were inoculated with Pseudomonas chlororaphis subspecies aureofaciens (1 × 109 CFU/mL) at sowing. The pots (12 cm x 14 cm) were kept at control conditions (16 h / 8 h day/ night; 24 °C day and 19 °C night). Drought stress was applied fourteen days after sowing. The growth of seedlings was monitored, and morphological and physiological parameters were recorded. Two weeks after the application of drought stress the plants were destroyed for biomass evaluation.
Various morphological and physiological parameters showed that bacterial application significantly (P <0.05) improved height (+3.6%), leaf chlorophyll (+17.5%), and plant fresh (+37%) and dry weight (+28.8%) and root fresh (+63.8%) and dry weight (61%) under drought in comparison with untreated plants. Significant interactions among variables (Genotype, Stress and Treatment) were observed in some parameters (height, root, shoot and total dry and fresh weight and Water use efficiency). Considering the dry weight of plants the best results were achieved by inoculated plants without drought stress followed by plant without inoculation and without emphasized textdrought stress, inoculated plants under drought stress and plant without inoculation and under drought stress. Considering water use efficiency, Pamina was the genotype that showed the highest values when inoculated with Pseudomonas chlororaphis subspecies aureofaciens whereas Ponente showed the highest results without inoculation.
Conclusively, our results showed that Pseudomonas chlororaphis subspecies aureofaciens has the potential to ameliorate drought tolerance in barley, however, other genotypes should be evaluated considered the interactions between genotype and treatment observed and the effect of PGPR should be also checked in field condition.