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- Combining ectomycorrhizal fungi and bacteria: a powerful tool to improve tree performancePublication . Ramos, Miguel A.; Sousa, Nadine R.; Franco, Albina R.; Dundar, Gonul; Oliveira, Rui S.; Castro, Paula M. L.Ectomycorrhizal fungi are ubiquitous to forest soils and the symbiosis between these microorganisms and plants roots is known to be essential for tree establishment and development, especially in areas of poor soil. Studies have also shown that some rhizosphere bacteria may act as plant stimulating agents and growth promoters. Additionally, bacteria and fungi strongly interact and therefore the analysis of the triangle plant-fungi-bacteria is a vital approach when aiming at the use of microbial inocula to enhance plant performance. To obtain a synergistic combination between microorganisms, a thorough selection is required since bacteria may strongly inhibit fungal growth, and vice versa, incurring in the risk of failed inoculum. In the present work we investigated the use of a dual inoculation system, consisting of a bacterial strain from the genus Mesorhizobium in combination with selected ectomycorrhizal fungi. In vitro tests were performed to assess the dynamic of co-culturing both microorganisms. The inoculum was applied at nursery stage and saplings were then transplanted into the field. Approximately 5000 seedlings were used in this experiment comprising the following species: Quercus suber, Quercus robur, Quercus rubra, Pinus pinaster and Pinus pinea. Seedlings were grown for 9 months in a commercial forest greenhouse and then transplanted to 4 locations in Portugal: Mindelo, Santo Tirso, Vila do Conde and Proença-a-Nova. Samples were taken at the end of nursery phase and 8 months after transplantation. Biometric and mycorrhizal parameters were analyzed and the persistence of the inoculated strains was evaluated. The presence of selected phytohormones was also determined. Results showed that the combined use of fungi-bacteria inoculum can be more effective than the use of each individual microbial partner. The use of ectomycorrhizal fungi and bacteria has great potential in forestry as a biotechnological tool to produce high performance plants at nursery stage and in the field.
- Impact of bacterial inoculation of Quercus suber on mycorrhization by Suillus species at early stages of tree developmentPublication . Ramos, Miguel A.; Sousa, Nadine R.; Franco, Albina R.; Dundar, Gonul; Oliveira, Rui S.; Castro, Paula M. L.Portugal accounts for approximately 50% of the world cork production. Quercus suber is the second most abundant tree in Continental Portugal, covering currently 737 thousand hectares and representing 23% of the forest area. This species is of paramount importance to the country both ecologically and economically. As many other forest species, Q. suber forms symbiotic associations with ectomycorrhizal (ECM) fungi with the hyphae acting as fine extensions of the plant root system allowing it to capture water and nutrients in exchange for photosynthetic carbohydrates. The use of bacteria as inoculum also has great potential in forestry, whether through their capability to act as plant growth promoters (PGPB) or/and as mycohhizal helper bacteria (MHB). The latter have a direct impact in promoting fungal symbiosis and could possibly represent the third link in the mycorrhizal partnership. However, the association between all vertices of the triangle (plant-fungi-bacteria) is highly specific and needs to be further explored when aiming at the use of microbial inocula in the tuning of mycorrhization at nursery stage. The aim of this work was to study the impact of inoculating Q. suber with a fungus belonging to the genus Suillus and a bacterial strain belonging to the genus Mesorhizobium, proven to be PGPB in preliminary studies. The experiment was conducted in a forest nursery in Amarante. After 9 months, the impact of inoculating with each microorganism individually was compared to that of the use of the combined inoculum. Biometric parameters were determined (shoot height, primary and secondary root length, shoot and root dry weight) and mycorrhizal parameters were assessed (percentage of ECM colonisation and expansion rate). The presence of selected phytohormones was also determined by HPLC. Overall, inoculated plants had a superior performance than the non-inoculated controls, in the majority of the parameters studied. The use of the combined inoculum was more successful than any other treatment in promoting shoot height and led to the highest concentration of indoleacetic acid (IAA). The results obtained suggest that the use of bacteria in the mycorrhization of Q. suber may positively affect plant in its early stage of development.
- The interaction between ectomycorrhizal fungi and growth promoting bacteria in plant development from in-vitro to the fieldPublication . Ramos, Miguel A.; Sousa, Nadine R.; Franco, Albina R.; Dundar, Gonul; Oliveira, Rui S.; Castro, Paula M. L.There is currently an array of biotechnological tools which may positively influence plant development and establishment. Symbiosis with ectomycorrhizal fungi is known to improve plant health by increasing nutrient and water uptake and alleviating environmental stresses. Some rhizosphere bacteria are also proven to act as plant stimulating agents, health managers and growth promoters. The use of a combined inoculum using both microorganisms has great potential in forestry. Nevertheless, the interaction between fungi and bacteria is highly specific and bacteria are known not only to enhance fungal growth (mycorrhiza promoting bacteria), but also to strongly inhibit it. It is therefore important to evaluate the compatibility between ectomycorrhizal fungi and bacteria and to determine the impact of such combination in plant development when aiming at the use of optimized microbial inoculum for enhancing plant growth. In the present work we investigated the use of a dual inoculation system, consisting of a bacterial strain from the genus Mesorhizobium in combination with ectomycorrhizal fungi, from in-vitro tests to a nursery stage followed by transplantation to the field. Approximately 5000 seedlings were used in these experiments comprising Quercus suber, Quercus robur, Quercus rubra, Pinus pinaster and Pinus pinea. Seedlings were grown for 9 months in a commercial forest greenhouse and then transplanted to 4 locations in Portugal. The first sampling was made before field transplantation. Results showed that the combined use of fungi-bacteria inoculum significantly influenced plant growth and its effect was different from that of each individual microbial partner, emphasizing the strong interaction between microorganisms.