Antifungal potential evaluation and alleviation of salt stress in tomato seedlings by a halotolerant plant growth-promoting actinomycete Streptomyces sp. KLBMP5084

Abstract

Salt stress affects plant growth and crop yield reduction, thus how to improve the salt tolerance of plants is full of challenges. Plant growth-promoting rhizobacteria (PGPR), as an environment-friendly treatment to improve salt stress tolerance of plants is widely accepted and has big potential in field application. In this study, a halotolerant actinomycete Streptomyces sp. KLBMP5084 obtained from the root of halophyte Limonium sinense was evaluated for antifungal activity in vitro and applied for the growth promoting of tomato seedlings under salt stress. Results demonstrated that the fermentation broth and the volatile organic compounds (VOCs) of strain KLBMP5084 could inhibit a variety of plant pathogenic fungi, including tomato early blight disease pathogenic fungi Alternaria solani. In particular, the KLBMP5084 inoculation significantly enhance the growth of tomato seedlings compared with the control after irrigating with 200 mM NaCl, with increased fresh weight, shoot length, and the number of fibrous roots. Further, the antioxidant enzymes activity, soluble sugar and proline contents in leaf and stem were also effectively increased, and malondialdehyde (MDA) was decreased. KLBMP5084 inoculation also increased the contents of K+ and Ca2+, reduced the Na+ accumulation in leaf. A total of 191 genes were also observed differentially expressed after KLBMP5084 treatment under salt stress in leaves by transcriptome analysis. Genes involved in the photosynthesis-antenna proteins pathway, isoquinoline alkaloid biosynthesis, zeatin biosynthesis and protein processing of endoplasmic reticulum pathway were enriched to the highest degree, indicating their significance and effects in response to salt stress in tomato seedlings. Collectively, these findings indicate that strain Streptomyces sp. KLBMP5084 has the potential as the biological fertilizer for promoting the tomato seedlings growth under salinity stress.