Plant growth-promoting effects of rhizospheric and endophytic bacteria associated with different tomato cultivars and new tomato hybrids

Gennaro Roberto Abbamondi,Panagiotis Gkorezis,Wouter Sillen,Barbara Nicolaus,Carmine Iodice,Nele Weyens,Wesley De Melo Rangel,Sofie Thijs,Jaco Vangronsveld,Giuseppina Tommonaro

doi:10.1186/s40538-015-0051-3

Abstract

Conventional agriculture relies on chemical pesticides and fertilizers, which can degrade ecosystems. A reduction of these harmful practices is required, replacing (or integrating) them with more eco-friendly approaches, such as microbial inoculation. Tomato is an important agricultural product, with a high content of bioactive compounds (folate, ascorbate, polyphenols, and carotenoids). The focus of this research was to investigate the plant growth-promoting (PGP) abilities of bacterial strains isolated from different tomato cultivars, with the aim to develop systems to improve plant health and crop productivity based on microbial inoculation. A pool of different tomato cultivars already available on the market and new tomato hybrids were selected based on their nutritional quality (high content of biologically active compounds). A total of 23 strains were isolated from tomato roots (11 rhizospheric strains and 12 root endophytes). The cultivable isolates were analyzed for a number of different PGP traits: organic acids (OA), indole acetic acid (IAA), ACC deaminase, and siderophore production. The effects of microbial inoculation on root growth of Arabidopsis thaliana were also evaluated using a Vertical Agar Plate assay. A high percentage of the isolated strains tested positive for the following PGP traits: 73 % were able to produce OA, 89 % IAA, 83 % ACC deaminase, and 87 % siderophores. The most striking result were remarkable increases in the formation of root hairs for most of the inoculated plants. This effect was obvious for all A. thaliana seedlings inoculated with the isolated endophytes, and for the 50 % of the seedlings inoculated with the rhizospheric strains. A better knowledge of the plant growth-promotion activity of these strains can provide an important contribution to increase environmental sustainability in agriculture.

Highlights

Conventional agriculture relies on chemical pesticides and fertilizers, which can degrade ecosystems
Agric. (2016) 3:1 be drawn between bacteria residing in the rhizosphere or phyllosphere and bacteria living inside the plant, the so-called endophytes
Genotypic characterization After the isolation, all morphologically different bacteria were purified, but only 2/3 of the strains showed to be cultivable in the subsequent steps; 16S rDNAbased identification was performed on 15 strains (6 rhizospheric and 9 endophytic strains)

Summary

Introduction

Conventional agriculture relies on chemical pesticides and fertilizers, which can degrade ecosystems. Established strategies to enhance crop productivity are the use of chemical fertilizers, manures, and pesticides These approaches often have a negative impact on the environment: leaching of nitrate into. Endophytic bacteria reside in specific tissues of the plant (such as root cortex or xylem) and develop a close association with the plant, with exchange of nutrients, enzymes (lipase, catalase, oxidase, etc.), functional agents (siderophores, biosurfactants, etc.), and “signals” [9, 10]. Endophytes colonize their plant host tissues in which they persist without exerting the negative effects of a pathogen (disruption of respiration, photosynthesis, translocation of nutrients, transpiration, etc.). Plant growth-promoting bacteria promote plant health and growth via three mechanisms: phytostimulation, biofertilization, and biocontrol [11]

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Results

Discussion

Conclusion