Role of Pseudomonas fluorescens in mitigating salinity stress in safflower (Carthamus tinctorius L.) through physio-biochemical responses

Salinity is an agricultural problem of great concern, at which, about one third of the world’s irrigated land is not in use. Several microorganisms such as fluorescent Pseudomonas, known to have the ability to tolerate high salt concentrations. Among these microorganisms, Pseudomonas fluorescens is plant growth promoting rhizobacterium and lives in the plant rhizosphere. This study was executed to evaluate the impact of Pseudomonas fluorescens on growth parameters and some biochemical constituents related to salinity in safflower (Carthamus tinctorius L.) Arak 12811 cultivar under salt stress.

Treatments, four levels salinity stress factor with sodium chloride salt (0, 5, 25, 50 and 150 mM) and two level inoculation factor (control and bacterium) as a factorial experiment in a completely randomized design with four replications was designed. Safflower seeds coated with growth promoting bacteria with 5% cellulose carboxymethyl and the plants grow in pots under different salt levels. After 40 days, root and shoot dry weight and relative water content measured under salt levels and bacterial inoculations. Also changes of chlorophyll a and b, carotenoides, proline, soluble sugars, glycine betaine and malondialdehyde contents were measured by chlorometric analysis.

The results showed that an increase in NaCl concentration in the nutrient solution reduced the height, shoot and root dry weight and chlorophyll a and b content in soybean plants while the amount of proline, soluble sugars, glycine betaine and malondialdehyde, increased. Safflower plants inoculated with P. fluorescens gave the highest significant increment in plant height, stem and root dry weights, chlorophyll a and b, carotenoides and relative water content under saline and non-saline conditions. Negative correlation between relative water content and total soluble sugars, glycine betaine and proline, show osmolytes accumulation for continued water uptake and reduced osmotic stress. The highest significant activity of proline, total soluble sugars and glycine betaine were recorded with inoculated plants irrigated with 150 mM NaCl solution. The bacterium inhibited malondialdehyde accumulation and decreased lipid peroxidation. Overall, this research revealed that seedlings inoculated with promoting growth bacterium until 50 mM salinity has provided most optimal performance and efficiency.

The present results revealed increases in safflower plant growth and biochemical constituents related to salinity by using of P. fluorescens, which could be suggested for improve plant salinity stress resistance.