Effect of Plant Growth-Promoting Rhizobacteria on Growth, Nodulation and Nutrient Accumulation of Lentil Under Controlled Conditions

Application of plant growth-promoting rhizobacteria （PGPR） has been shown to increase legume growth and development under field and controlled environmental conditions. The present study was conducted to isolate plant growth-promoting rhizobacteria （PGPR） from the root nodules of lentil （Lens culinaris Medik.） grown in arid/semi-arid region of Punjab, Pakistan and examined their plant growth-promoting abilities. Five bacterial isolates were isolated, screened in vitro for plant growth-promoting （PGP） characteristics and their effects on the growth of lentil were assessed under in vitro, hydroponic and greenhouse （pot experiment） conditions. All the isolates were Gram negative, rod-shaped and circular in form and exhibited the plant growth-promoting attributes of phosphate solubilization and auxin （indole acetic acid, IAA） production. The IAA production capacity ranged in 0.5-11.0μg mL-1 and P solubilization ranged in 3-16 mg L-1. When tested for their effects on plant growth, the isolated strains had a stimulatory effect on growth, nodulation and nitrogen （N） and phosphorus （P） uptake in plants on nutrient-deficient soil. In the greenhouse pot experiment, application of PGPR significantly increased shoot length, fresh weight and dry weight by 65%, 43% and 63% and the increases in root length, fresh weight and dry weight were 74%, 54% and 92%, respectively, as compared with the uninoculated control. The relative increases in growth characteristics under in vitro and hydroponic conditions were even higher. PGPR also increased the number of pods per plant, 1 000-grain weight, dry matter yield and grain yield by 50%, 13%, 2870 and 29%, respectively, over the control. The number of nodules and nodule dry mass increased by 170% and 136%, respectively. After inoculation with effective bacterial strains, the shoot, root and seed N and P contents increased, thereby increasing both N and P uptake in plants. The root elongation showed a positive correlation （R2 = 0.67） with the IAA production and seed yield exhibited a positive correlation （R2 = 0.82） with root nodulation. These indicated that the isolated PGPR rhizobial strains can be best utilized as potential agents or biofertilizers for stimulating the growth and nutrient accumulation of lentil.