The Fungi Life Cycle

BY ARI SINGER

You’ve decided to add beneficial microbes to your growing process for the first time and are dabbling with the idea of adding mycorrhizal fungi to the mix. You head over to the nearest grow shop and get a recommendation from the sales rep to pick up product X. You excitedly head home and apply the product to your plants. Congratulations! But, what exactly is in the bag that you purchased? How does it work? How can a living organism arrive in a sealed bag and affect and benefit your plants?

Let’s talk about the role of mycorrhizal fungi in nature and why adding them to growing media benefits plants. Arbuscular mycorrhizal fungi (AMF) associate with approximately 90% of all plants on the planet, can be found on almost every continent, and have been around for over 400 million years. The mycorrhizal fungi penetrate root cells, and from there, branch out into the soil in search of nutrients. Plants exchange these nutrients for carbohydrates they give to the fungi. As a result, mycorrhizal plants can absorb more nutrients and water through the fungi’s hyphal network.

Most commercial mycorrhizal inoculants consist of the following: spores, hyphae, and inoculated root fragments. Propagules are effective inoculation vehicles and can be made up of any of these three elements. Some products contain only spores, while other “whole inoculum” products contain all three. Whole inoculum products tend to be more robust and can inoculate plants at higher rates.

Fungi in Commercial Products

When picking up your first pack, look at what the product contains in terms of fungal species and their concentrations. This is essential since the higher the concentration of propagules, the faster and more likely they are to colonize the roots. Since we are dealing with biological products, it’s important to observe how they were stored and their shelf life. If the product has expired, do not purchase it. If it has been stored outside and not according to manufacturer recommendations, do not purchase it either, as this could certainly affect the viability of the fungi inside the product. There have been cases where products do not meet the label’s claims and get taken off the shelf by regulatory agencies, which can happen due to improper storage that kills off the fungi.

In a bag or bottle of a commercial product, propagules can come in several forms. Viable, meaning alive, or non-viable, meaning dead. The viable propagules in the product arrive in a dormant state and spring to life by two factors. Either biotic, through a hormonal signal from a plant the moment the fungi are placed in the growing media, or abiotic, from a change in environmental conditions, i.e., rain, cold, drought, etc. If there is an abiotic factor that caused the fungi to come to life and no plant for the fungi to connect with and create the mycorrhizal symbiosis, the fungi will die.

Methods of Producing Mycorrhizal Fungi:

In-vitro – This is done in sterile Petri dishes on “transformed root cultures” where the host “plant”, mostly carrot, has been modified to produce only roots to have the fungi grow on. This method provides uncontaminated fungal propagules but has some disadvantages as well. The fungi are produced in sterile, artificial conditions, and thus, there is no interaction with the external biological world. Various biotic and abiotic stressors affect the fungi and how they will perform in a pot or a field (Vasilis Kokkoris and Miranda Hart, bit.ly/3kRQBJ1). These stimuli include the fungi’s interaction with various microbes, temperature, carbon levels, and more.

In-vivo – This method is done by growing fungi on the roots of living host plants. Since approximately 90% of all plants form a relationship with AMF, the number of potential host plant species is vast, allowing the fungi to be stimulated by the different growth rates, nutrient uptake cycle, and host plants’ other factors. These plants are grown mostly in pots in greenhouses with soil or other growing media. While they are in a greenhouse, the rhizosphere environment is more complicated than in a Petri dish. This means that there is an interaction between microbes and the fungi, an influence of the nutrients used to feed the plants, the watering schedule, the temperature, and more.

In a product containing the whole inoculum, the sum of these propagules is estimated via what is known as Inoculum Potential (LIU, R.-J., & LUO, X.-S. 1994). Therefore, by adding more root fragments, the Infection Potential grows. Moreover, studies show that root fragments containing vesicles and hyphae increase colonization speed compared with spores (Powell, 1976; Abbot and Robson 1981), and specifically, vesicles in roots proved to be highly infectious (Biermann and Linderman). Therefore, the benefits of whole inoculum are faster initial colonization, and higher inoculum potential.

This doesn’t mean a product with only spores is inferior to a product with all three types of propagules. There are other factors to consider, such as the propagules’ viability to that of the spores alone. These tests are done at labs where they test the strength of the inoculant by various methods.

Each method has its advantages and disadvantages, and more research needs to be done on the subject to fully understand the impact of both approaches in an agricultural setting.

Nature vs. Controlled Environment

How does growing in a pot compare with what happens in nature from a mycorrhizal fungus’ standpoint and role? In nature, AMF can connect multiple plants, even from different species, together through their hyphal network. This phenomenon has been coined the “Wood Wide Web”. Through this network, plants exchange nutrients and water, and even information, among themselves. Plants can communicate with each other through this intricate network and inform each other of pests so that other plants can increase their defence mechanism and much more. When growing a single plant in a pot, this network exists, but not to its fullest extent. The fungi’s role is lessened, as they do not transfer nutrients between plants or information, but their part is still enormous. They now will “only” absorb nutrients that the plant can’t access, such as locked up phosphorous, iron, zinc, and others, as well as water.

Endomycorrizal Fungi Life Cycle

What came first, the chicken or the egg? What’s fascinating about mycorrhizal inoculants is that both the spore (A.K.A. the egg) and the hyphae (the chicken) can start a symbiotic relationship with a plant. Spores sporulate and make their way toward the plant cell, where they construct treelike structures called arbuscules, where the exchange of nutrients and carbohydrates between the fungi and plant occurs. From there, the fungus branches out via hyphae, microscopic root-like structures in search of food for the plant. When inoculating with hyphae and root fragments, the hyphae do not require sporulation and can latch on to the plant roots without sporulating.

Mycorrhizal fungi are obligate biotrophs, meaning they will live only if they have a host plant. If no host plant is around, the spores or hyphae will either remain dormant or ultimately die. Unlike humans, who digest food internally, mycorrhizal fungi secrete powerful enzymes as they spread out in the soil, which break down minerals and nutrients into simpler forms. It is through this method that the fungi feed the plant. As they continue to expand into unchartered territories that the plant can’t reach, they supply the plant with the brokendown matter which the plant needs to grow. In return for this, the plant gives carbohydrates to the fungi.

BIO

Ari Singer is a man with a mission: spreading endomycorrhizal fungi spores to benefit plants worldwide. He leads the DYNOMYCO sales team in the USA, Canada, UK, Australia, and Israel and is passionate about mycology, gardening, and making the world more sustainable. Ari has a B.A. in Sustainability & Economics from the Interdisciplinary Center in Herzliya. When he is not roaming the globe spreading DYNOMYCO spores, you can find him on his urban garden rooftop growing vegetables and mushrooms or on a slackline somewhere between cliffs and trees.