Mycorrhizal Association in Cannabis Cultivation

The practice of Cannabis cultivation is broadly extensive, thanks to the relentless effort of experts towards finding better methods and techniques for the improvement of yield quality and quantity. Before now, issues arose from poor nutrient uptake, pests, diseases, and many others. These challenges encountered, facilitated the discovery and development of newer, more efficient methods - one of which is the mycorrhizal association in cannabis.

Millennials ago, when plants first moved from water to land, they lacked specialized root systems and relied on fungi for their water and nutrient absorption. This handicap remained even after the development of specialized roots, with some plants existing as obligate mycotrophs and some as facultative mycotrophs.

Understanding Mycorrhiza

Mycorrhiza is a mutualistic association between fungi and a plant. The term ”mycorrhiza” describes the specialized fungus present in the symbiotic relationship within the plant’s rhizosphere.

Types of Mycorrhiza

There are three known types of mycorrhiza, classified based on their symbiotic method:

• Ectomycorrhiza – the hyphae coating of plant’s root. Most ectomycorrhiza belongs to the family Basidiomycetes, Ascomycetes, and seldom, Zygomycetes.  It is recognized as the most advanced form of mycorrhiza.

• Endomycorrhiza – the intracellular penetration of the plant’s root by fungal filaments. The endomycorrhiza is further classified into three major groups and two minor groups. They are sequential as follows:

• Arbuscular
• Orchidaceous
• Ericoid
• Monotropoid
• Arbutoid

• Ectendomychorrhiza – this exhibits both characters of the endo- and ectomycorrhizal  - coating the root’s surface but showing intracellular penetration of the root’s cortex.

Mycorrhizal Association in Cannabis

Although cannabis thrives well in the absence of a mycorrhizal association, it is still categorized as an obligate mycotroph. Because in the presence of the association, it has been found to flourish better, maximizing cultivation output.

Of the five forms of endomycorrhiza, the most proven beneficial type in Cannabis cultivation is the arbuscular mycorrhizal, specifically the species Glomus intraradices and Glomus mosseae, due to their exceptional potential in inoculating cannabis’ roots.

Mechanism of Action

The arbuscular mycorrhizal begins colonization by creating an appressorium, from which the hyphae emerges, to penetrate inter-cellularly and intracellularly the cannabis’ root’s cortex. The fungus’ filamentous hyphae spread radially through the soil, enhancing nutrient and water uptake by reaching soil regions that the cannabis’ roots cannot get to.

In return, the plant supplies certain minerals necessary for the fungus’ growth. The fungus additionally secretes metabolic by-products like glomalin, (a glycoprotein).  These by-products are functional in the improvement of soil structure and quality.

Infecting Cannabis

The popular question on the artificial application of Mycorrhizal is, “why apply mycorrhizal if it is already available in the soil?”

The need for the artificial application of mycorrhizal in a non-sterile soil is determined by the quantity of mycorrhizal present and their distance from the plant’s roots. This will determine the time taken to establish a mycorrhizal association and is critical to the plant’s growth and development.

To avoid destroying the plants and reaping maximum output, the plant’s root should be infected at multiple sites to allow for faster development of the colonization process. The minimum amount required for infection is dependent on the age and size of the cannabis’ root system.

Mycorrhizal Supplements

Similar to the pharmaceutical multivitamins and agricultural fertilizers, mycorrhizal supplements are added to make up for fungus deficits in geoponics or fixation of suitable mycorrhizal in hydroponics.

Most manufactured mycorrhizal is made up of 2 or more fungi and are highly heat-labile. It is often not recommended to add manufactured mycorrhizal to soil due to several reasons, the most pressing being the effect of foreign fungi species on the native plant (different soil regions).

However, in certain situations, there is a need for the inculcation of manufactured mycorrhizal to cannabis cultivation. The following are exceptional cases to warrant its addition:  

• Bare soil
• Hydroponics
• Sterile soil

Note: The terms  ’bare soil’ and ’sterile soil’ are commonly misapplied and frequently used interchangeably. These are, however, two distinct terms.  Bare soil is ground with no plant growth, while sterile soil is dirt with no fungal growth.

A Little Too Much

As the saying goes, “too much of anything is bad,” this applies to the cannabis - mycorrhizal association. As much as the symbiosis is a certified beneficial relationship, application or the presence of excess mycorrhizal in culture can lead to the inhibition of cannabis growth as a result of excessive absorption of certain minerals not required or needed in micro quantities.

Fungicides and Mycorrhizae

In the use of mycorrhizal inoculants, the effect of fungicides on the association should be considered. Ironically, some fungicides enhance the development of mycorrhizal, while others can be harmful to the mycorrhizal fungi.

Also, in the application of fungicides, foliar application of non-systemic fungicides tends to have minimal or zero effect on the root’s fungi. Soil-drenched application of non-systemic fungicides, on the other hand, can produce a detrimental effect on the root’s fungi.

Nonetheless, on total invagination of the plant’s root, the mycorrhizal fungi might be less susceptible to harmful but non-systemic fungicides due to lesser fungicide levels in the root. Generally, systemic fungicides are fatal to mycorrhizal fungi.

Benefits

In conclusion, the following are the overall  benefits of the symbiont,  arbuscular endomycorrhiza to cannabis cultivation:

• Enhanced growth and yield quality.
• Improved drought tolerance of the Cannabis plant.
• Controlled soil erosion.
• Decreased susceptibility to disease pathogens.
• Better soil quality and structure.
• Inhibition of undesirable plants’  growth.