Asymbiotic mass production of the arbuscular mycorrhizal fungus Rhizophagus clarus

Abstract

Arbuscular mycorrhizal (AM) symbiosis is a mutually beneficial interaction between fungi and land plants and promotes global phosphate cycling in terrestrial ecosystems. AM fungi are recognised as obligate symbionts that require root colonisation to complete a life cycle involving the production of propagules, asexual spores. Recently, it has been shown that Rhizophagus irregularis can produce infection-competent secondary spores asymbiotically by adding a fatty acid, palmitoleic acid. Furthermore, asymbiotic growth can be supported using myristate as a carbon and energy source for their asymbiotic growth to increase fungal biomass. However, the spore production and the ability of these spores to colonise host roots were still limited compared to the co-culture of the fungus with plant roots. Here we show that a combination of two plant hormones, strigolactone and jasmonate, induces the production of a large number of infection-competent spores in asymbiotic cultures of Rhizophagus clarus HR1 in the presence of myristate and organic nitrogen. Inoculation of asymbiotically-generated spores promoted the growth of host plants, as observed for spores produced by symbiotic culture system. Our findings provide a foundation for the elucidation of hormonal control of the fungal life cycle and the development of inoculum production schemes.

The arbuscular mycorrhizal fungus Rhizophagus clarus improves physiological tolerance to drought stress in soybean plants

“…The AMF of the genus Rhizophagus (= Glomus 38 ) can survive and multiply in semi-arid ecosystems, even under conditions of low water availability 39 , and Rhizophagus clarus produces larger spores than other species, such as R. irregularis and R. intraradices 40 . Given this, R. clarus has received considerable attention, especially as it can grow symbiotically, using the myristate as a source of carbon and energy 41 , 42 .…”

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

“…For instance, the propagation of AMF with different host plants and nutrient solutions can be easily tested. Recent studies showed that R. irregularis (Sugiura et al 2020) and R. clarus (Tanaka et al 2022) can grow on medium supplied with fatty acids or lipids under asymbiotic conditions. The hydration of the grains of SAP with a solution containing palmitoleic acid or myristate could improve the spore production in the SAP-based autotrophic culture.…”

Functions of Lipids in Development and Reproduction of Arbuscular Mycorrhizal Fungi

“…Rhizophagus irregularis cultured in a modified M medium (A), a modified M medium with 100 μM C16:0 FA (B), a T medium without C14:0 FA (C) and a T medium that contains 500 μM C14:0 FA (D) [(A, B) Kameoka et al. 2019b , (C, D) Tanaka et al. 2022 ].…”