The combined effects of Pseudomonas fluorescens and Tuber melanosporum on the quality of Pinus halepensis seedlings

Abstract

The ecological, economic and social values of the ectomycorrhizal fungi of the black truffle found in the rural Mediterranean are well known. The inoculation of Pinus halepensis seedlings with mycorrhizal fungi and rhizobacteria can improve the morphology and physiology of the seedlings and benefit the regeneration of arid regions and the reintroduction of inocula of mycorrhizal fungi into these areas. Some rhizobacteria can improve the establishment and functioning of ectomycorrhizal symbiosis. In this study, seedlings of P. halepensis were inoculated with the mycorrhizal fungus Tuber melanosporum and the rhizobacteria Pseudomonas fluorescens CECT 844 under non-limiting greenhouse conditions. Five months after inoculation, we analysed the growth, water parameters (osmotic potential at saturation, osmotic potential at turgor loss and modulus of elasticity), concentrations of mycorrhizal colonies, nutrient concentration and nutrient contents (N, P, K, Ca, Mg and Fe) in roots and aerial parts of the seedlings. Subsequently, tests were performed to estimate the root growth potentials. None of the treatments changed the water parameters or growth potentials of the roots. The inoculations improved the growth and nutrient uptake of the seedlings, although the combination of P. fluorescens CECT 844 and T. melanosporum did not generally lead to a significant improvement over the positive effects of a simple inoculation of T. melanosporum; however, the addition of P. fluorescens CECT 844 did double the rate of the mycorrhization of T. melanosporum. These results may be promising for enhancing the cultivation of truffles.

The combined effects of Pseudomonas fluorescens CECT 844 and the black truffle co-inoculation on Pinus nigra seedlings

“…We previously demonstrated that the inoculation of P. halepensis seedlings with P. fluorescens CECT 844 rhizobacteria and the black truffle T. melanosporum improved plant growth and the N absorption of seedlings, and that the addition of P. fluorescens CECT 844 doubled the mycorrhization rate of T. melanosporum (Dominguez et al 2012). In the present study, inoculations (both combined and single) were performed using T. melanosporum and P. fluorescens CECT 844 in P. nigra seedlings.…”

“…1). However, we have demonstrated that P. fluorescens CECT 844 can facilitate the formation and establishment of T. melanosporum ectomycorrhizae in P. halepensis seedlings under non-optimal soil pH conditions, when calcium carbonate is not added to the growing peat substrate (Dominguez et al 2012). According to Garbaye & Duponnois (1993), MHB are not plant-specific, but they are clearly selective in their interactions with various fungal species, being therefore fungus-specific.…”

“…We recently demonstrated that the inoculation of Aleppo pine (Pinus halepensis Mill.) with P. fluorescens CECT 844 improved the vegetative growth and N absorption of the P. halepensis seedlings (Dominguez et al 2012).…”

“…The adhesion of and colonization by mycorrhizal helper bacteria (MHB), such as P. fluorescens, on the surfaces of several ectomycorrhizae can improve the symbiotic relationship and the presymbiotic stages, and can benefit the host plant , Deveau et al 2007). In some cases, the co-inoculation of mycorrhizal fungi and P. fluorescens may also increase the root colonization by Pseudomonas (Ouahmane et al 2009, Dominguez et al 2012, and the mycorrhizal fungus. In other cases, synergistic effects on the plant growth were observed (Rincón et al 2007), although co-inoculation did not affect the fungal colonization.…”

“…We recently demonstrated that the inoculation of Aleppo pine (Pinus halepensis Mill.) with P. fluorescens CECT 844 improved the vegetative growth and N absorption of the P. halepensis seedlings (Dominguez et al 2012).The use of environmental-friendly natural microbial inocula, such as PGPR or mycorrhizal fungi, is presented in this study as a potential alternative fertilizers. These microorganisms are also beneficial for the maintenance of pre-existing soil microflora, thus contributing to the conservation of soil biodiversity.…”