Abstract
Stenotrophomonas maltophilia is a plant growth-promoter. This bacterium is also implicated in human diseases. Thus, after the use of this bacterium in agriculture, the safety of the final products has to be verified. Due to the ubiquitous presence of S. maltophilia in soil, in this study a massive contamination was simulated to evaluate the growth and safety of Raphanus sativus L.. Different inoculums and soil treatment conditions were tested. Soils were analysed weekly and the radishes at harvest for their microbial loads and presence/persistence of S. maltophilia LMG 6606. The concentration of the bacterium added in the different trials decreased during the first week, but increased thereafter and determined a significant increase of growth parameters of radishes. The addition of S. maltophilia LMG 6606 to non-autoclaved soil enhanced the productivity of radishes. The bacterium did not internalize in the hypocotyls, but colonized the external surface ensuring the safety of the products. Thus, a sanitizing bath of hypocotyls before consumption is necessary.
Highlights
The experimental plan included eight different conditions for the growth of radish plants: ASS, autoclaved soil inoculated with S. maltophilia LMG 6606; AS, autoclaved soil added with Ringer’s solution (Sigma-Aldrich, Milan, Italy); nASS, non-autoclaved soil inoculated with S. maltophilia LMG 6606; nAS, non-autoclaved soil added with Ringer’s solution; ASSwS, autoclaved soil weekly inoculated with S. maltophilia LMG 6606; ASwR, autoclaved soil weekly added with Ringer’s solution; nASSwS, nonautoclaved soil weekly inoculated with S. maltophilia LMG 6606; nASwR, non-autoclaved soil weekly added with Ringer’s solution
The autoclaved soil uninoculated showed a Total mesophilic count (TMC) of 3.53 Log CFU gdw−1 and, surprisingly, the bacterial load estimated on vancomycin–imipenem–amphotericin B (VIA) was at almost 2 Log CFU gdw−1, whereas the non-autoclaved un-inoculated soil showed levels of ca. 7 Log CFU gdw−1 on both Plate Count Agar (PCA) and VIA media
The concentrations on VIA evaluated for the trials weekly added with S. maltophilia LMG 6606 (ASSwS and nASSwS) showed trends almost comparable to those displayed by the corresponding trials not subjected to the weekly additions (ASS and nASS), but the levels estimated for the second were slightly lower
Summary
This bacterium is implicated in human diseases. After the use of this bacterium in agriculture, the safety of the final products has to be verified. Due to the ubiquitous presence of S. maltophilia in soil, in this study a massive contamination was simulated to evaluate the growth and safety of Raphanus sativus L. Cultivated plants may suffer nutritional stresses when the amount or availability of soil nutrients is lower than that required for sustaining metabolic processes in each growth stage [1]. Restoring of nutrients and enhancing their availability by improving soil characteristics and efficiency of plants, are the main objectives of the modern agriculture. Sustainable agricultural production systems may be obtained by enhancing the uptake efficiency of nutrient Lowering the use of chemical inputs and the search for alternative ways to improve a more sustainable agriculture is a current challenge [2].
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