Poor Quality of Commercial Arbuscular Mycorrhizal Inoculants Used for Agriculture and Home Gardening

ABSTRACT There is an urgent need to develop microbial inoculants that can consistently improve crop performance as part of efforts to implement sustainable agricultural practices and reduce the environmental impact of intensive farming. One of the best known examples of beneficial soil microbes that can promote plant growth and ecosystem performance are arbuscular mycorrhizal fungi (AMF). AMF‐based inoculants are increasingly being marketed to enhance key ecosystem functions such as soil nutrient uptake, soil structure, carbon storage and ecosystem health. Despite this potential, the efficacy of commercial AMF products is still poorly documented and highly variable. In this study, we evaluated 16 commercially available AMF inoculants (nine marketed for agricultural use and seven for home gardening) and, for comparison, seven AMF inoculants for research propose, all tested under controlled greenhouse conditions. Our findings revealed that only three commercial AMF products led to root colonisation, and only one promote plant growth. One‐third of the agricultural inoculants colonised plant roots, whereas none of the seven commercial home gardening products successfully established a symbiosis with plant roots. In contrast, products intended for research purposes consistently induced AMF colonisation and often resulted in a positive growth response, likely due to higher propagule density. Together with three recent studies analysing worldwide AMF products, our study revealed that 85% of the 64 commercial arbuscular mycorrhizal inoculants tested are of poor quality and did not colonise plant roots. Thus, standardised quality control across the industries is necessary to ensure product effectiveness and promote widespread acceptance by farmers, as well as successfully spreading the use of mycorrhizal inoculants as a viable tool for enhancing sustainable agricultural and gardening practices.