A simple and low-cost technique to initiate single-spore cultures of arbuscular mycorrhizal fungi using a superabsorbent polymer

Abstract

Most species of arbuscular mycorrhizal fungi (AMF) are propagated with a host plant in a pot culture. However, the soil matrix makes it difficult to monitor the establishment and development of the symbiosis. In vitro culturing using Ri T-DNA transformed roots provides a clear medium and a sterile environment which offsets the constraints of the soil matrix. Nevertheless, the sterile conditions and the Ri T-DNA transformed roots provide very different growing conditions compared to a pot culture. Transparent soil based on superabsorbent polymer (SAP) has the potential of combining the advantages of current in vivo and in vitro culture methods without the constraints associated with either technique (opacity and sterility). Here we describe a SAP-based autotrophic culture as an alternative to current in vivo and in vitro culture methods. This system using two-compartment Petri dishes makes it easy to initiate single-spore cultures and to monitor fungal propagation. The SAP-based autotrophic system allowed the establishment of single-spore cultures of seven species (Diversispora varaderana, Funneliformis geosporus, Gigaspora rosea, Racocetra fulgida, Rhizophagus irregularis, R. intraradices and Sclerocystis sp.) from six genera and three families. Cultures were maintained over several months under non-sterile conditions. The Petri dishes avoid the problem of cross contamination and they can be stacked for space optimization. The grains of SAP colonized with new spores were used as inoculum to initiate new cultures in the SAP-based system. The SAP-based autotrophic culture method is a low-cost and low-tech approach, which makes the study of AMF much more accessible.