Claims checked › Claim
The fungi on the label are in the bag
“A commercial mycorrhizal product contains live fungi of the species listed on the label, at the propagule count stated, and they will colonise your crop.”
Independent tests on three continents say mostly not. Of 25 products, 84% produced no root colonisation in sterile soil and one raised plant growth. Of 11 products sequenced, two contained none of the labelled species and all but one contained undeclared ones. Some products do work, which is why this is contested and not retired.
Where it comes from
Product labels stating species and propagules per gram, and the reasonable assumption that a regulated agricultural input contains what it says.
Who benefits
Every producer and distributor; a market that one 2025 meta-analysis estimates wastes US$876 million a year on products that do not colonise (as reported).
What the evidence says
Viability. Salomon and colleagues (2022) tested 28 commercial inoculants across Australia, Europe and North America. In the 25 European and Australian greenhouse bioassays, in non-sterile soil none raised colonisation and one in 25 raised biomass; in sterile soil 84% produced no root colonisation, "demonstrating that these products did not contain viable propagules", while laboratory Rhizophagus irregularis colonised 48% and 79% of root length (abstract). Koziol and colleagues (2024) found propagule counts "up to 100%" out from spore counts, contamination with the pathogen Olpidium, and no growth benefit once the fertiliser mixed into products was controlled for (abstract). Their 2025 meta-analysis puts 84% of commercial products under 5% colonisation and fewer than 12% both colonising and helping, against 63% of laboratory cultures (as reported; paper). A Zurich study of 16 commercial products is titled "Poor quality of commercial arbuscular mycorrhizal inoculants" (paper).
Identity. Sequencing 11 products from four producers, the University of Tartu found nine with at least one labelled species, two with none, and all but one with species not on the label (abstract).
Why contested and not retired. Some products do colonise, the Swiss research strain clearly established in a quarter of fields, and the Greek barley trial with a Czech product reported a small gain. The claim is true of a minority of bags and there is no way to tell which from the label.
Regulation does not check. EU Regulation 2019/1009 lets CE-marked biostimulants contain mycorrhizal fungi and requires substantiated claims, but nothing tests viability at the point of sale; storage heat and fungicide seed dressings kill spores after any test.
What to say instead
"Ask for an independent colonisation test on this batch." If the supplier cannot provide one, assume the 84%. The mycorrhizal inoculation page explains what to do with the fungi you already have.