Fodder radish aqueous extracts and associated rhizobacteria as bio-stimulants on tomato growth

Abstract

ABSTRACT Use of bio-stimulants can reduce amounts of synthetic chemicals for improving tomato (Solanum lycopersicum L.) growth and production. The investigation evaluated the rhizobacterial isolates B45, B46, B48, B54 and B55 associated with fodder radish (Raphanus sativus L.) and its aqueous extracts for their ability to promote growth of tomato plants under greenhouse conditions. Rhizobacteria were applied by root dipping followed by seedling drenching at planting. The isolates were characterized, based on macro-morphological and biochemical traits, and mechanisms involved in Plant Growth-Promoting (PGP) features were explored. For direct PGP traits, isolates were able to fix nitrogen on N-free agar medium. Isolates B45, B46, B54 and B55 were positive for indole-3-acetic acid production; isolates B46, B48 and B55 were positive for phosphate solubilization with the highest activity exhibited by B46. For indirect PGP traits, isolates were chitinase-, lipase-, and amylase-producing agents. Based on phylogenetic analysis of the 16S rDNA, the most bioactive isolate B46 was affiliated to Bacillus vallismortis (OK083726). All isolates displayed antifungal activity against soil-borne fungi Aspergillus niger, Penicillium digitatum, Fusarium oxysporum, F.sambucinum, and Trichoderma harzianum. Fodder radish aqueous extracts were tested at 5, 7.5, 10 or 15% (w:v). Chemical characterization by spectrophotometer of compounds indicated presence of auxin and polyphenols. Fodder radish aqueous extract displayed antifungal activity against all fungal species. Fodder radish appears to be a natural source for isolation of potent PGP rhizobacterial isolates and/or secondary metabolites bioactive for promotion of tomato growth and with an antifungal potential.