Isolation of auxin- and 1-aminocyclopropane-1-carboxylic acid deaminase-producing bacterium and its effect on pepper growth under saline stress

Abstract

Plant tissues produce ethylene under the environmental stresses such as drought, salinity, and heavy metals. Ethylene concentration can be reduced by 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase produced by plant growth-promoting rhizobacterium (PGPR), which cleaves the ethylene precursor ACC. The present study focused on alleviation of environmental stress by selected PGPR, which could suppress fungal plant disease. These PGPRs were capable of utilizing ACC as sole source of nitrogen and also produced auxin. Seed germination of red pepper was reduced with increasing salt concentration, and approximately 98.2% of seeds germinated in the absence of salt, whereas only 36.2% seeds germinated in the presence of 175 mM NaCl. Seed germination was also decreased by 62.1 and 19.9% in the presence of 120mM NaCl and 120mM NaCl +ACC deaminase-producing PGPR Pseudomonas fluorescens 2112, respectively, compared to uninoculated control. The effect of salinity stress with different salt concentration on pepper plants and their alleviation with PGPR was evaluated. Non-inoculated pepper plants died after 5 week when grown in the presence of high salt (120 mM NaCl), whereas 80% of pepper plants inoculated with P. fluorescens 2112 survived under the high salt stress. Salt stress also decreased the fresh and dry weights of pepper grown, compared to the negative control, whereas pepper plants inoculated with P. fluorescens 2112 retained the biomass similar to control plants. These results indicate that ACC deaminase and auxin producing P. fluorescens 2112 is a multi-functional PGPR that can promote the growth and development of pepper plants by alleviating the high-salt stress.