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History of the Glomeromycetes in vitro collection

For about two decades, Agriculture and Agri-Food Canada (AAFC) research on arbuscular mycorrhizal (AM) symbioses has emphasized the studies of AM fungi, biodiversity of indigenous and agricultural soils, and the establishment of AM fungi reference dry and living collections and their classification. The objective of this research is to evaluate the potential of AM mycorrhizal strains on diverse crop plants and to develop modern tools for their detection and propagation. AM fungi cultivation faces a major handicap as they are obligate symbionts, meaning that these fungi cannot be cultivated and moreover cannot survive without their mycorrhizal association with plants.

Traditionally propagated in pot cultures, called in vivo cultures the AAFC collections contain hundreds of AM fungi strains developed for taxonomic, biochemical, horticultural and agronomical investigations. The production on inoculum using in vivo propagation systems necessitates specialized installations (greenhouses and growth chambers) and expensive labour time for the maintenance and evaluation of cultures as well as constant monitoring to prevent cross-contamination between cultures and to maintain their monospecificity.

Figure 8: In vivo culture in Sunbags©

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During the 1980s, the improvement of technologies related to the cultivation of excised roots allowed the successful cultivation of some AM fungi strains. Using this methodology, the tracability of monoxenic cultures (root and fungi) can be followed throughout several generations by simply transferring a mature section of a colony to a new substrate. Maintained in Petri dishes, these cultures can provide laboratories continuous access to contaminant-free fungal material (Fortin et al 2002).

Figure 9: In vitro culture on excised roots

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Contrarily to in vivo propagated AM fungi, colony development, life cycle, spore ontogeny and AM fungi interaction with diverse organisms or treatments can be directly followed through the dissecting microscope without disturbing fungal growth. Moreover, hundreds of cultures can be grown in a single incubator and the resulting inoculum products are particularly appropriate to serve as starting inoculum for research and development projects (Declerck et al. 2005).

Figure 10: In vitro culture collection

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Due to the numerous applications offered by the in vitro propagation methodology, scientists realized the research potential of in vitro propagated AM fungi. Several species and strains were then successfully propagated that way, thereby establishing a reference culture collection of AM fungi such as the GINCO (Declerck & Dalpé 2001).

The most famous AM fungi strain at GINCO is undisputedly Glomus irregulare. The strain DAOM 181602, 197198 (formerly authentified as G. intraradices) is the one chosen for the whole genome sequencing project started some years ago. It is the only AMF strain actually authorized for sale by the Canadian Food Inspection Agency. It is the mycorrhizal constituent of numerous commercialized inoculum produced in Canada and abroad (Faye et al. 2012). Among the other strains held by GINCO are high-value organisms with plant growth potential over a variety of cultivated plant and other potentially resistant to high salinity environments, to heavy metal soil contamination and to polycyclic aromatic hydrocarbons.

Figure 11: Spores of Glomus irregulare

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