Mycorrhiza Don't Like to Share With Endophytes.

­So I have talked several times about the wonders of Mycorrhizal relationships, but did you know that not all fungi growing on roots fit into this group? It’s true, and these colonizers, known as endophytes, run the full gambit of beneficial to pathogenic for their host. What is a plant to do? Well, a new study out in PLOS One suggests the best course of action is to hope for a true mycorrhizal symbiosis to help keep their neighbors in check.

Mycorriza Reduces Adverse Effects of Dark Septate Endophytes (DSE) on Growth of Conifers

The team of Vanessa Reininger and Thomas Sieber looked at the effects of colonization by Phialocephala fortinii and Acephala applanata, a couple of ascomycetes that like to room together under the acronym PAC, with and without the presence of a common mycorrhizal fungi named Laccaria bicolor.

Laccaria bicolor

The PAC combination is routinely isolated from root tips throughout the Northern Hemisphere. It is in fact the most common complex and thus the main component of the Dark Septate Endophytes, a group of fungi identifiably by their… you guessed it, darkly pigmented septates. While these colonizers can sometimes be beneficial to the host plant they can sometimes be pathogenic and harmful instead.

There have been several studies on endophytes interacting with plants, and several on mycorrhizal relationships, but this study seeks to complete the circle and find out the interplay these two groups have with each other. Since both are clear hosts of L. bicolor and PAC in nature, the scientists chose to study these interactions on the Douglas fir and Norway spruce.

To do this the research team incubated L. bicolor into growth tubes for five and a half weeks, and then planted sterile seeds into said tubes. After allowing the plants to grow for another three and a half weeks they inoculated their roots with one of four PAC strains. Each combination, as well as a completely fungus-free control, was then grown at both 19°c and 25°c. The trees were grown for five months after inoculation under these conditions and root segments were excised for analyses. Each sample was measured for plant biomass, root vs. shoot growth ration, and fungal biomass.

One major factor across all data points was the growth temperature. On all plants this significantly altered both plant growth and colonization rates of both mycorrhiza and endophytes. But this study was meant to focus on the relationship of mycorrhiza and endophyte so I will too.

PAC strains were able to more densely colonize on Douglas fir then they were on Norway spruce as well as at the lower 19°c temperature. Mycorrhized plants significantly decreased the growth of PAC in both plants. It is noted by the researchers however that we have to take into account that L. bicolor was allowed to colonize before the inoculation of PAC.

The biomass of trees was also increased in the presence of mycorrhyzation compared to PAC. The fungal-free controls performed or outperformed both of these though.

Lastly the plants colonized solely by PAC invested more into root growth than both the controls and those with a mycorrhizal relationship. This means mycorrhizal symbiosis allowed the plant to focus on shoot production instead of fighting for nutrients with its fungus.

The researchers demonstrated that mycorrhization by Laccaria bicolor handily kept the team of Phialocephala fortinii and Acephala applanata from getting out of control; letting both the Douglas fir and Norway spruce get on with its day to day routine. Since all of these fungi live in close relation to each other in the wild the team speculated that this same mechanism is in play.


Awesome researchers:

Vanessa Reininger, & Thomas N. Sieber (2012). Mycorrhiza Reduces Adverse Effects of Dark Septate Endophytes (DSE) on Growth of Conifers PLoS One DOI: 10.1371/journal.pone.0042865

Photo cred:
US Department of Energy via Wikimedia