Abstract
One of the bottlenecks in mycorrhiza research is that arbuscular mycorrhizal fungi (AMF) have to be cultivated with host plant roots. Some AMF species, such as Rhizophagus irregularis, can be grown in vitro on dual-compartment plates, where fungal material can be harvested from a fungus-only compartment. Plant roots often grow into this fungus compartment, and regular root trimming is required if the fungal material needs to be free of traces of plant material. Trimming also increases unwanted contamination by other microorganisms. We compared 22 different culture types and conditions to a widely used dual-compartment culture system that we refer to as the “standard system.” We found two modified culture systems that allowed high spore production and low rates of contamination. We then compared the two modified culture systems with the standard system in more detail. In the two modified culture systems versus the standard system, a comparable number of spores were produced per plate, the necessity for root trimming was reduced, and there was significantly diminished contamination in the fungal compartment. A cost analysis showed that both modified culture systems were more economic than the standard culture system for the production of the same number of non-contaminated spores. The two modified culture systems provide an economic alternative for the production of contaminant-free fungal material which is ideal for studies requiring AMF DNA or RNA for genetics, genomics, and transcriptomic studies or for studies requiring relatively large amounts of fungal material for greenhouse experiments.
Highlights
Rhizophagus irregularis is an arbuscular mycorrhizal fungus (AMF) that forms mutualistic symbioses with the roots of most land plants, improving their growth and resistance to environmental stress (Smith and Read 2010)
We aimed to improve the production of R. irregularis spores in the dual-compartment culture system that were free of contamination with microorganisms and plant material and that could be quickly produced without the necessity of root trimming
Cultures established with the standard culture system and with large plate systems in which root trimming was performed (Table 1; ID 1 and 2 and 15 and 16) were more susceptible to contamination with microorganisms than the cultures in the same culture systems in which root trimming was not performed (Table 1; ID 3 and 4 and 17 and 18)
Summary
Rhizophagus irregularis is an arbuscular mycorrhizal fungus (AMF) that forms mutualistic symbioses with the roots of most land plants, improving their growth and resistance to environmental stress (Smith and Read 2010). R. irregularis can be produced in vitro for laboratory and greenhouse use or as a commercial inoculum that can be used to increase yields of commonly grown crop plants, such as potato (Wu et al 2013; Hijri 2016), wheat (Al-Karaki et al.2004), and cassava (Ceballos et al 2013). For these reasons, the genomics, genetics, and transcriptomics of R. irregularis are being studied extensively in order to better understand the molecular genetics of plant-AMF interactions and to produce a more effective inoculum (Sanders 2010). The Pc is inoculated with R. irregularis that colonizes the carrot roots
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