Do Mushrooms need Light?

Some types of mushrooms do need light, some don’t.

Back in 1980, Eger-Hummel placed mushrooms into four different categories according to their need for light (Fig. 1).

Group A: Light and darkness play no role at any stage of fruiting body development.

Group B: Light and darkness play no role in primordium formation, but the light is required at later stages of mushroom development.

Group C: Light is required except for a short period at an early stage of development when darkness is essential.

Group D: Light is required at all stages of fruiting body development.

Figure 1: Requirements for fruiting in mushrooms[1]

But a word of caution. Not every mushroom can be placed precisely into one of these four categories. This is mainly due to the complex mechanisms which are still not all well understood. Therefore, it can happen that one mushroom, which is, for example, in category D, actually belongs to category B[2].

Examples for each of these four categories are[3]:

Group A: Agaricus bisporus

Group B: Lentinus tigrinus

Group C: Coprinus congregatus

Group D: Favolus arcularius

Why some mushrooms need light, and some don’t, we can only understand by looking at the mushroom cycle itself.

What is the Mushroom Cycle?

In general, the mushroom cycle (Fig. 2) can be divided into two phases – vegetative phase and reproductive phase. “The vegetative stage is referred to […] as the spawn running phase[4]” and “the reproductive stage as the fructification phase.[5]”

Figure 2: Mushroom life cycle[6]

Let’s dive a little bit deeper into this fascinating world.

We start with the spore, which produces a primary mycelium. “A mycelium is a vast network of interconnected cells that permeates the ground and lives perennially.[7]”

The growth of the mycelium “results in a fusion of the hyphae and a close association of the hyphae with the substrate.[8]”

This growth happens during the vegetative phase.

The part of a fungus that we usually call a mushroom is the fruiting body of a fungus. The building of the fruiting bodies only occurs if there are triggers that signal the fungus to initiate the process and get ready to reproduce.

Such triggers can be a change in temperature, a change in the CO2/O2 ratio, and or light (Fig. 3).

Two phases: vegetative and reproductive phase

Figure 3: The two major phases of mushroom growth and development[9]

Now to grow mushrooms ourselves, we have, therefore, emulate the nature of the fungus we want to grow.

How are mushrooms sensing light?

It was found that some fungi contain genes that are responsible for the circadian clock, which itself is linked to light. These genes are called white collar-1 (WC-1) and white collar-2 (WC-2) and are part of the LOV (light-oxygen-voltage) domain. These two genes respond to blue light and act like photoreceptors.

After finding these two genes, researchers starting to look into other mushrooms and found similar genes, for example, in Lentinula edodes (Shiitake) and Pleurotus ostreatus (Oyster mushroom).

The photoreceptors in Shiitake are called Le.phrA and Le.phrB and are primarily active during the fruiting body stage.

In a science paper from 2015, the author[10] mentioned that no WC-1 or similar gene was found in Pleurotus spp. which would mean that Oyster mushroom doesn’t respond to blue light. But in a recent article, two similar genes were announced[11]. They are called PoWC1 and PoWC2.

In addition to the blue light photoreceptors, it could be shown that there are red light and far-red light photoreceptors (phytochromes) within some mushrooms[12].

How to trigger pinhead formation?

If we, for example, want to grow Oyster mushrooms (Pleurotus spp.), we need a phase of darkness and a phase at which we will introduce light.

Let’s start with the inoculation of our spawn material. Here we transfer a piece of mycelium from a petri dish and place it onto our spawn material. The mycelium then starts to grow through it and, by doing so, expands. This happens totally in darkness. There is no light needed. Quite the opposite.

The time to fully colonize our spawn material depends on the quantity of the substrate itself and the growing conditions – mainly temperature.

After the spawn material is fully colonized, we then transfer a part (around 5 %) onto our primary substrate. And the process starts again. After the substrate is again fully colonized, we want to “tell” the fungi to produce fruiting bodies.

How long does it take to fully colonize a substrate?

Depending on the quantity of the substrate and the growing conditions (temperature, humidity, and CO2 level) it can take a while in order to colonize the substrate fully.

Table 1 gives you an overview of how long it can take to colonize your spawn and your substrate fully. As shown in this table, it can take up to 70 days to fully colonize the substrate. But only 14 days is possible as well.

That means besides the quantity of our substrate and the growing conditions, the mushroom species you want to grow influences the speed of colonization.

If you want to learn more about the impact of different parameters on the time to fully colonize your substrate you can find more information in my article How long does it take to colonize a bag fully?

Table 1: Overview of different growing conditions for various mushroom species[13]

As said, after the substrate is fully colonized, we want to trigger the fungi. In doing so, we move from the vegetative phase to the reproductive phase (Fig. 3). These triggers are called environmental factors.

An example of this point can be seen in figure 4. Hereafter 14 days, the light level is increased from 0 Lux to over 1,200 Lux. This level is kept for 4 more days and then lowered to just below 800 Lux.

This process step triggers the formation of pinheads (Primordia), which then will grow into the fruiting bodies, aka mushrooms we can harvest.

Figure 4: Example of light intensity during the cultivation[14]

An important side notes: The amount of light you expose your mushroom and the type of light has a high impact on the growth of your fungi[15].

But as shown in figure 1, not all mushrooms need light or to be more precise, the change darkness/brightness to start pinning.

Summary

If the light is needed and how much depends on the type of mushroom and the phase, the fungus is in.

During the spawn run, they don’t need light at all.

To initiate the pinhead formation (which means moving from the vegetating phase to the reproductive phase), light is for some mushroom types needed.

This is true as well during the growth phase of the fruiting bodies.

If you want to improve your yield than the right lighting can help you to do so. You will find more information in my article “How light will impact your mushroom yield.