RhizobacteriumBacillus subtilisreduces toxic effects of high electrical conductivity in soilless culture of lettuce

Abstract

Quality of irrigation water is a critical factor for greenhouse production. A high concentration of soluble salts is the main reason for high electrical conductivity (EC) of irrigation water. The low water quality available for agriculture is the main problem in many places of the world. Plant growth-promoting bacteria are free-living soil bacteria that can help plant growth without having pathogenic effects. In the current study, three concentrations of NaCl (0, 40 and 80 mM, which resulted in EC of 1, 4 and 8 mS, respectively) were added to the irrigation water. Half of the salt-treated plants were fed with the rhizobacterium Bacillus subtilis (OD=0.6) to test whether it can reduce the problems of medium and high EC of irrigation water on lettuce plants, cultivated in Perlite medium. Growth parameters, including fresh and dry weights, leaf area, leaf number and plant height of control plants, were considerably improved by application of B. subtilis in the root medium of lettuce plants. Furthermore, the growth of plants exposed to medium and high EC was improved by the presence of B. subtilis in their rhizosphere. Polyphasic chlorophyll fluorescence transient parameters such as absorption flux, trapping flux and quantum yield for energy dissipation were decreased in plants with B. subtilis in their rhizosphere, while electron transport flux per reaction center was increased in B. subtilis-treated plants. In conclusion, B. subtilis can be used in the root medium of greenhouse plants to prevent the toxic effects of high EC of irrigation water.