The Effect of Plant Growth Promoting Rhizobacteria Inoculation on Wheat Growth Indices in Saline Irrigation Conditions

There are many sources of saline water that can be used in agriculture by adopting specific methods. Considering that salinity stress reduces the growth of plants, including wheat, Therefore, any technology that increases wheat's tolerance to salinity stress is very important. The use of plant growth promoting rhizobacteria (PGPR) is one of the strategies based on sustainable development to reduce the effects of stress in agricultural production. In this research, five strains of selected PGPR were used which were screened based on different plant growth stimulating characteristics. The ability of the strains to salinity tolerance at electrical conductivity (EC) values of 5, 10, 15 and 20 dS.m-1 was evaluated. A factorial greenhouse experiment was conducted based on the completely randomized design in three replicates under salinity stress conditions during a period of 100 days using wheat cultivar Narin in the year 2020 at the central station of the Soil and Water Research Institute. Salinity stress was applied through irrigation with saline water at four levels with electrical conductivity of 0.40 (normal water), 6, 10 and 14 dS.m-1. The inoculation factor included levels without inoculation and inoculation with Pseudomonas putida P186, P. fluorescens P187, P. sp P241, Azotobacter chroococcum Azto478 and A443 and Azospirillum lipoferum strains. Two milliliters of inoculum per seed was inoculated with a population of 1.5 x 108 during cultivation. The laboratory results showed that all strains did not show any growth reduction up to a salinity of 20 dS.m-1. The results of the greenhouse experiment showed that irrigation with saline water had significant reducing effects on all growth indices. Stress at the levels of 6, 10 and 14 14 dS.m-1 caused a decrease of 13.5, 35 and 57% of shoot wet weight, respectively. Also, the mentioned levels caused a decrease of 37.5, 50 and 55% of shoot dry weight, respectively. The root dry weight decreased by 80, 87 and 91%. Plant height decreased by 11, 17, and 18%, head length by 16, 25, and 31%, and head number by 23, 31, and 45%, respectively, at different salinity levels. Inoculation with selected bacteria did not show a significant effect on any of the wheat growth indices under salinity stress conditions. In this research, it was concluded that the reasons for the lack of significant effect of inoculation could be the resistance of the Narin variety to salinity and the inability of the bacteria to make the plant more tolerant to salinity conditions or the growth-promoting properties of the bacteria being unaffected in these conditions.