Symbiotic bacteria in tree roots promote the growth of mycorrhizal fungi

• Bacterial community on ectomycorrhizal roots of Laccaria laccata in a chestnut plantation
• Extending the hyphal area of the ectomycorrhizal fungus Laccaria parva co-cultured with ectomycorrhizosphere bacteria on nutrient agar plate

Keisuke Obase (a)

(a) Department of Mushroom Science and Forest Microbiology, FFPRI, Tsukuba, Ibaraki, Japan.

• Mycoscience, 60(1):40-44, January 2019 DOI：10.1016/j.myc.2018.08.002( External link )
• Mycoscience, 60(2):95-101, March 2019 DOI：10.1016/j.myc.2018.12.002( External link )

Ectomycorrhizal fungi, such as Tricholoma matsutake and Tuber spp., live symbiotically in tree roots to form ectomycorrhizal structures through which trees provide nutrients for mushrooms to emerge. In addition to trees, various microorganisms in the soil around mycorrhizae are likely to have an impact on the emergence of mushrooms of ectomycorrhizal fungi; however, such relationships have not been fully clarified. In this study, we first investigated bacterial flora surrounding the ectomycorrhizae of Laccaria parva (formerly described as L. laccata in Japan), an ectomycorrhizal fungus. As a result, we frequently identified bacteria of the Rhizobiales order. These bacteria include species involved in nutrient dynamics, such as Bradyrhizobium spp., the most frequently found group of bacteria that are occasionally involved in the nitrogen cycle. Subsequently, we performed dual-culture testing on a plate medium to clarify how these bacteria surrounding the ectomycorrhizae affect the hyphal elongation of L. parva. The results showed that some bacteria, including Bradyrhizobium, did not affect or promote the hyphal elongation of L. parva, whereas the majority of bacteria evaluated tended to inhibit hyphal elongation. These bacteria may be useful in improving the growth of L. parva to the emergence of mushrooms and the function of ectomycorrhizal fungi. I plan to investigate the effects of these bacteria on mycorrhizal development and mushroom emergence and eventually develop a cultivation technology for mushrooms of ectomycorrhizal fungi.
 

Figure Mushrooms (left) and a mycorrhiza (right) of Laccaria parva.

Figure Dual-culture testing of Laccaria parva and a bacterium. A hyphal piece of L. parva was placed at the center, and 1-cm linear smears of a bacterium were placed at four positions (triangles). The left image shows the control plate inoculated without bacteria. The right image shows the plate inoculated with Bradyrhizobium. 1bar = 1cm.