Trends in Horticulture (2020) Volume 3 Issue 1 doi:10.24294/th.v3i1.1786 55 Original Research Article Combination of phosphorus mobilizing and solubilizing fungi with phosphoric rocks and volcanic materials for growth promotion of let- tuce (Lactuca sativa L.) plants María Silvana Velázquez 1* , Marta Noemí Cabello 1,2 , Lorena Alejandra Elíades 1 , María L. Russo 1 , Natalia Alle- grucci 1 , Santiago Schalamuk 3 *1 Instituto de Botánica Carlos Spegazzini, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Buenos Aires, Argentina. E-amil: mariasvelazquez@yahoo.com.ar 2 Comisión de Investigaciones Científicas (CIC), La Paz, Buenos Aires, Argentina. 3 Centro de Química Inorgánica, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Universidad Nacional de La Plata, La Plata, Buenos Aires, Argentina. ABSTRACT Arbuscular mycorrhizal fungi (AMF) increase the uptake of soluble phosphates, while phosphorus solubilizing fungi (S) promote the solubilization of insoluble phosphate complexes, together benefiting plant nutrition. The use of these organisms in combination with minerals or rocks that provide nutrients is another alternative to maintain crop productivity. The objective of this work was to combine AMF and S with pyroclastic materials (ashes and pumicites) from the Puyehue volcano and phosphoric rocks (PR) from the Río Chico Group (Chubut) and to evaluate the performance of these mixtures as substrates for potted production of Lactuca sativa. To formulate the substrates, a mixture of Ter-rafertil® with ashes was used as a base. Penicillium thomii was the S and spores of the fungus Rhizophagus intraradices (AEGIS® Irriga) served as the source of AMF. Various combinations of microorganisms and the addition or not of RP were evaluated. The treatments were: (1) substrate; (2) substrate + AMF; (3) substrate + S; (4) substrate + AMF + S; (5) substrate: PR; (6) substrate: PR + AMF; (7) substrate: PR + S, and (8) substrate: PR + AMF + S. There were 3 replicates per treatment. The parameters evaluated were total and assimilable P content in the substrate, P in plant tissue and dry biomass. All of them were significantly higher in the plants grown in the substrate added with PR and inoculated with S and AMF. This work confirms that the S/AMF combination with volcanic ashes from Puyehue and PR from Grupo Río Chico formulated with a commercial substrate promote the growth of L. sativa. Thus, it is possible to increase the added value of geomaterials of national origin. Keywords: Solubilizing Fungus DEP; P-mobilizing Fungi; Phosphate Rock; Volcanic Ashes ARTICLE INFO Received: 1 June 2020 Accepted: 22 July 2020 Available online: 26 July 2020 COPYRIGHT Copyright © 2020 by author(s). Trends in Horticulture is published by En- Press Publisher LLC. This work is licensed under the Creative Commons Attribution- NonCommercial 4.0 International License (CC BY-NC 4.0). https://creativecommons.org/licenses/by- nc/4.0/ 1. Introduction Arbuscular mycorrhizal fungi (AMF) and phosphorus (P)-solubiliz- ing microorganisms present in the rhizosphere play an important role in the growth and development of their host plants [1] . AMF (phylum Glom- eromycota) increase the uptake of soluble phosphates in the plant sur- roundings [2,3] , while P-solubilizing fungi (S) promote the solubilization of insoluble phosphate complexes [1,4–7] . This process is achieved through acydification and chelation, as well as by ion exchange reactions and pro- duction of low molecular weight organic acids, such as gluconic, citric and oxalic acids [8,9] . Another alternative use to maintain plant productivity is the combi- nation of different mineral materials in the growth substrate, which